Merge branch 'drm-next-4.12' of git://people.freedesktop.org/~agd5f/linux into drm...

[mirror_ubuntu-bionic-kernel.git] / arch / x86 / xen / enlighten_pv.c

/*
 * Core of Xen paravirt_ops implementation.
 *
 * This file contains the xen_paravirt_ops structure itself, and the
 * implementations for:
 * - privileged instructions
 * - interrupt flags
 * - segment operations
 * - booting and setup
 *
 * Jeremy Fitzhardinge <jeremy@xensource.com>, XenSource Inc, 2007
 */

#include <linux/cpu.h>
#include <linux/kernel.h>
#include <linux/init.h>
#include <linux/smp.h>
#include <linux/preempt.h>
#include <linux/hardirq.h>
#include <linux/percpu.h>
#include <linux/delay.h>
#include <linux/start_kernel.h>
#include <linux/sched.h>
#include <linux/kprobes.h>
#include <linux/bootmem.h>
#include <linux/export.h>
#include <linux/mm.h>
#include <linux/page-flags.h>
#include <linux/highmem.h>
#include <linux/console.h>
#include <linux/pci.h>
#include <linux/gfp.h>
#include <linux/memblock.h>
#include <linux/edd.h>
#include <linux/frame.h>

#include <xen/xen.h>
#include <xen/events.h>
#include <xen/interface/xen.h>
#include <xen/interface/version.h>
#include <xen/interface/physdev.h>
#include <xen/interface/vcpu.h>
#include <xen/interface/memory.h>
#include <xen/interface/nmi.h>
#include <xen/interface/xen-mca.h>
#include <xen/features.h>
#include <xen/page.h>
#include <xen/hvc-console.h>
#include <xen/acpi.h>

#include <asm/paravirt.h>
#include <asm/apic.h>
#include <asm/page.h>
#include <asm/xen/pci.h>
#include <asm/xen/hypercall.h>
#include <asm/xen/hypervisor.h>
#include <asm/xen/cpuid.h>
#include <asm/fixmap.h>
#include <asm/processor.h>
#include <asm/proto.h>
#include <asm/msr-index.h>
#include <asm/traps.h>
#include <asm/setup.h>
#include <asm/desc.h>
#include <asm/pgalloc.h>
#include <asm/pgtable.h>
#include <asm/tlbflush.h>
#include <asm/reboot.h>
#include <asm/stackprotector.h>
#include <asm/hypervisor.h>
#include <asm/mach_traps.h>
#include <asm/mwait.h>
#include <asm/pci_x86.h>
#include <asm/cpu.h>

#ifdef CONFIG_ACPI
#include <linux/acpi.h>
#include <asm/acpi.h>
#include <acpi/pdc_intel.h>
#include <acpi/processor.h>
#include <xen/interface/platform.h>
#endif

#include "xen-ops.h"
#include "mmu.h"
#include "smp.h"
#include "multicalls.h"
#include "pmu.h"

void *xen_initial_gdt;

RESERVE_BRK(shared_info_page_brk, PAGE_SIZE);

static int xen_cpu_up_prepare_pv(unsigned int cpu);
static int xen_cpu_dead_pv(unsigned int cpu);

struct tls_descs {
        struct desc_struct desc[3];
};

/*
 * Updating the 3 TLS descriptors in the GDT on every task switch is
 * surprisingly expensive so we avoid updating them if they haven't
 * changed.  Since Xen writes different descriptors than the one
 * passed in the update_descriptor hypercall we keep shadow copies to
 * compare against.
 */
static DEFINE_PER_CPU(struct tls_descs, shadow_tls_desc);

/*
 * On restore, set the vcpu placement up again.
 * If it fails, then we're in a bad state, since
 * we can't back out from using it...
 */
void xen_vcpu_restore(void)
{
        int cpu;

        for_each_possible_cpu(cpu) {
                bool other_cpu = (cpu != smp_processor_id());
                bool is_up = HYPERVISOR_vcpu_op(VCPUOP_is_up, xen_vcpu_nr(cpu),
                                                NULL);

                if (other_cpu && is_up &&
                    HYPERVISOR_vcpu_op(VCPUOP_down, xen_vcpu_nr(cpu), NULL))
                        BUG();

                xen_setup_runstate_info(cpu);

                if (xen_have_vcpu_info_placement)
                        xen_vcpu_setup(cpu);

                if (other_cpu && is_up &&
                    HYPERVISOR_vcpu_op(VCPUOP_up, xen_vcpu_nr(cpu), NULL))
                        BUG();
        }
}

static void __init xen_banner(void)
{
        unsigned version = HYPERVISOR_xen_version(XENVER_version, NULL);
        struct xen_extraversion extra;
        HYPERVISOR_xen_version(XENVER_extraversion, &extra);

        pr_info("Booting paravirtualized kernel %son %s\n",
                xen_feature(XENFEAT_auto_translated_physmap) ?
                        "with PVH extensions " : "", pv_info.name);
        printk(KERN_INFO "Xen version: %d.%d%s%s\n",
               version >> 16, version & 0xffff, extra.extraversion,
               xen_feature(XENFEAT_mmu_pt_update_preserve_ad) ? " (preserve-AD)" : "");
}
/* Check if running on Xen version (major, minor) or later */
bool
xen_running_on_version_or_later(unsigned int major, unsigned int minor)
{
        unsigned int version;

        if (!xen_domain())
                return false;

        version = HYPERVISOR_xen_version(XENVER_version, NULL);
        if ((((version >> 16) == major) && ((version & 0xffff) >= minor)) ||
                ((version >> 16) > major))
                return true;
        return false;
}

static __read_mostly unsigned int cpuid_leaf5_ecx_val;
static __read_mostly unsigned int cpuid_leaf5_edx_val;

static void xen_cpuid(unsigned int *ax, unsigned int *bx,
                      unsigned int *cx, unsigned int *dx)
{
        unsigned maskebx = ~0;

        /*
         * Mask out inconvenient features, to try and disable as many
         * unsupported kernel subsystems as possible.
         */
        switch (*ax) {
        case CPUID_MWAIT_LEAF:
                /* Synthesize the values.. */
                *ax = 0;
                *bx = 0;
                *cx = cpuid_leaf5_ecx_val;
                *dx = cpuid_leaf5_edx_val;
                return;

        case 0xb:
                /* Suppress extended topology stuff */
                maskebx = 0;
                break;
        }

        asm(XEN_EMULATE_PREFIX "cpuid"
                : "=a" (*ax),
                  "=b" (*bx),
                  "=c" (*cx),
                  "=d" (*dx)
                : "0" (*ax), "2" (*cx));

        *bx &= maskebx;
}
STACK_FRAME_NON_STANDARD(xen_cpuid); /* XEN_EMULATE_PREFIX */

static bool __init xen_check_mwait(void)
{
#ifdef CONFIG_ACPI
        struct xen_platform_op op = {
                .cmd                    = XENPF_set_processor_pminfo,
                .u.set_pminfo.id        = -1,
                .u.set_pminfo.type      = XEN_PM_PDC,
        };
        uint32_t buf[3];
        unsigned int ax, bx, cx, dx;
        unsigned int mwait_mask;

        /* We need to determine whether it is OK to expose the MWAIT
         * capability to the kernel to harvest deeper than C3 states from ACPI
         * _CST using the processor_harvest_xen.c module. For this to work, we
         * need to gather the MWAIT_LEAF values (which the cstate.c code
         * checks against). The hypervisor won't expose the MWAIT flag because
         * it would break backwards compatibility; so we will find out directly
         * from the hardware and hypercall.
         */
        if (!xen_initial_domain())
                return false;

        /*
         * When running under platform earlier than Xen4.2, do not expose
         * mwait, to avoid the risk of loading native acpi pad driver
         */
        if (!xen_running_on_version_or_later(4, 2))
                return false;

        ax = 1;
        cx = 0;

        native_cpuid(&ax, &bx, &cx, &dx);

        mwait_mask = (1 << (X86_FEATURE_EST % 32)) |
                     (1 << (X86_FEATURE_MWAIT % 32));

        if ((cx & mwait_mask) != mwait_mask)
                return false;

        /* We need to emulate the MWAIT_LEAF and for that we need both
         * ecx and edx. The hypercall provides only partial information.
         */

        ax = CPUID_MWAIT_LEAF;
        bx = 0;
        cx = 0;
        dx = 0;

        native_cpuid(&ax, &bx, &cx, &dx);

        /* Ask the Hypervisor whether to clear ACPI_PDC_C_C2C3_FFH. If so,
         * don't expose MWAIT_LEAF and let ACPI pick the IOPORT version of C3.
         */
        buf[0] = ACPI_PDC_REVISION_ID;
        buf[1] = 1;
        buf[2] = (ACPI_PDC_C_CAPABILITY_SMP | ACPI_PDC_EST_CAPABILITY_SWSMP);

        set_xen_guest_handle(op.u.set_pminfo.pdc, buf);

        if ((HYPERVISOR_platform_op(&op) == 0) &&
            (buf[2] & (ACPI_PDC_C_C1_FFH | ACPI_PDC_C_C2C3_FFH))) {
                cpuid_leaf5_ecx_val = cx;
                cpuid_leaf5_edx_val = dx;
        }
        return true;
#else
        return false;
#endif
}

static bool __init xen_check_xsave(void)
{
        unsigned int err, eax, edx;

        /*
         * Xen 4.0 and older accidentally leaked the host XSAVE flag into guest
         * view, despite not being able to support guests using the
         * functionality. Probe for the actual availability of XSAVE by seeing
         * whether xgetbv executes successfully or raises #UD.
         */
        asm volatile("1: .byte 0x0f,0x01,0xd0\n\t" /* xgetbv */
                     "xor %[err], %[err]\n"
                     "2:\n\t"
                     ".pushsection .fixup,\"ax\"\n\t"
                     "3: movl $1,%[err]\n\t"
                     "jmp 2b\n\t"
                     ".popsection\n\t"
                     _ASM_EXTABLE(1b, 3b)
                     : [err] "=r" (err), "=a" (eax), "=d" (edx)
                     : "c" (0));

        return err == 0;
}

static void __init xen_init_capabilities(void)
{
        setup_clear_cpu_cap(X86_BUG_SYSRET_SS_ATTRS);
        setup_force_cpu_cap(X86_FEATURE_XENPV);
        setup_clear_cpu_cap(X86_FEATURE_DCA);
        setup_clear_cpu_cap(X86_FEATURE_APERFMPERF);
        setup_clear_cpu_cap(X86_FEATURE_MTRR);
        setup_clear_cpu_cap(X86_FEATURE_ACC);
        setup_clear_cpu_cap(X86_FEATURE_X2APIC);

        if (!xen_initial_domain())
                setup_clear_cpu_cap(X86_FEATURE_ACPI);

        if (xen_check_mwait())
                setup_force_cpu_cap(X86_FEATURE_MWAIT);
        else
                setup_clear_cpu_cap(X86_FEATURE_MWAIT);

        if (xen_check_xsave()) {
                setup_force_cpu_cap(X86_FEATURE_XSAVE);
                setup_force_cpu_cap(X86_FEATURE_OSXSAVE);
        } else {
                setup_clear_cpu_cap(X86_FEATURE_XSAVE);
                setup_clear_cpu_cap(X86_FEATURE_OSXSAVE);
        }
}

static void xen_set_debugreg(int reg, unsigned long val)
{
        HYPERVISOR_set_debugreg(reg, val);
}

static unsigned long xen_get_debugreg(int reg)
{
        return HYPERVISOR_get_debugreg(reg);
}

static void xen_end_context_switch(struct task_struct *next)
{
        xen_mc_flush();
        paravirt_end_context_switch(next);
}

static unsigned long xen_store_tr(void)
{
        return 0;
}

/*
 * Set the page permissions for a particular virtual address.  If the
 * address is a vmalloc mapping (or other non-linear mapping), then
 * find the linear mapping of the page and also set its protections to
 * match.
 */
static void set_aliased_prot(void *v, pgprot_t prot)
{
        int level;
        pte_t *ptep;
        pte_t pte;
        unsigned long pfn;
        struct page *page;
        unsigned char dummy;

        ptep = lookup_address((unsigned long)v, &level);
        BUG_ON(ptep == NULL);

        pfn = pte_pfn(*ptep);
        page = pfn_to_page(pfn);

        pte = pfn_pte(pfn, prot);

        /*
         * Careful: update_va_mapping() will fail if the virtual address
         * we're poking isn't populated in the page tables.  We don't
         * need to worry about the direct map (that's always in the page
         * tables), but we need to be careful about vmap space.  In
         * particular, the top level page table can lazily propagate
         * entries between processes, so if we've switched mms since we
         * vmapped the target in the first place, we might not have the
         * top-level page table entry populated.
         *
         * We disable preemption because we want the same mm active when
         * we probe the target and when we issue the hypercall.  We'll
         * have the same nominal mm, but if we're a kernel thread, lazy
         * mm dropping could change our pgd.
         *
         * Out of an abundance of caution, this uses __get_user() to fault
         * in the target address just in case there's some obscure case
         * in which the target address isn't readable.
         */

        preempt_disable();

        probe_kernel_read(&dummy, v, 1);

        if (HYPERVISOR_update_va_mapping((unsigned long)v, pte, 0))
                BUG();

        if (!PageHighMem(page)) {
                void *av = __va(PFN_PHYS(pfn));

                if (av != v)
                        if (HYPERVISOR_update_va_mapping((unsigned long)av, pte, 0))
                                BUG();
        } else
                kmap_flush_unused();

        preempt_enable();
}

static void xen_alloc_ldt(struct desc_struct *ldt, unsigned entries)
{
        const unsigned entries_per_page = PAGE_SIZE / LDT_ENTRY_SIZE;
        int i;

        /*
         * We need to mark the all aliases of the LDT pages RO.  We
         * don't need to call vm_flush_aliases(), though, since that's
         * only responsible for flushing aliases out the TLBs, not the
         * page tables, and Xen will flush the TLB for us if needed.
         *
         * To avoid confusing future readers: none of this is necessary
         * to load the LDT.  The hypervisor only checks this when the
         * LDT is faulted in due to subsequent descriptor access.
         */

        for (i = 0; i < entries; i += entries_per_page)
                set_aliased_prot(ldt + i, PAGE_KERNEL_RO);
}

static void xen_free_ldt(struct desc_struct *ldt, unsigned entries)
{
        const unsigned entries_per_page = PAGE_SIZE / LDT_ENTRY_SIZE;
        int i;

        for (i = 0; i < entries; i += entries_per_page)
                set_aliased_prot(ldt + i, PAGE_KERNEL);
}

static void xen_set_ldt(const void *addr, unsigned entries)
{
        struct mmuext_op *op;
        struct multicall_space mcs = xen_mc_entry(sizeof(*op));

        trace_xen_cpu_set_ldt(addr, entries);

        op = mcs.args;
        op->cmd = MMUEXT_SET_LDT;
        op->arg1.linear_addr = (unsigned long)addr;
        op->arg2.nr_ents = entries;

        MULTI_mmuext_op(mcs.mc, op, 1, NULL, DOMID_SELF);

        xen_mc_issue(PARAVIRT_LAZY_CPU);
}

static void xen_load_gdt(const struct desc_ptr *dtr)
{
        unsigned long va = dtr->address;
        unsigned int size = dtr->size + 1;
        unsigned pages = DIV_ROUND_UP(size, PAGE_SIZE);
        unsigned long frames[pages];
        int f;

        /*
         * A GDT can be up to 64k in size, which corresponds to 8192
         * 8-byte entries, or 16 4k pages..
         */

        BUG_ON(size > 65536);
        BUG_ON(va & ~PAGE_MASK);

        for (f = 0; va < dtr->address + size; va += PAGE_SIZE, f++) {
                int level;
                pte_t *ptep;
                unsigned long pfn, mfn;
                void *virt;

                /*
                 * The GDT is per-cpu and is in the percpu data area.
                 * That can be virtually mapped, so we need to do a
                 * page-walk to get the underlying MFN for the
                 * hypercall.  The page can also be in the kernel's
                 * linear range, so we need to RO that mapping too.
                 */
                ptep = lookup_address(va, &level);
                BUG_ON(ptep == NULL);

                pfn = pte_pfn(*ptep);
                mfn = pfn_to_mfn(pfn);
                virt = __va(PFN_PHYS(pfn));

                frames[f] = mfn;

                make_lowmem_page_readonly((void *)va);
                make_lowmem_page_readonly(virt);
        }

        if (HYPERVISOR_set_gdt(frames, size / sizeof(struct desc_struct)))
                BUG();
}

/*
 * load_gdt for early boot, when the gdt is only mapped once
 */
static void __init xen_load_gdt_boot(const struct desc_ptr *dtr)
{
        unsigned long va = dtr->address;
        unsigned int size = dtr->size + 1;
        unsigned pages = DIV_ROUND_UP(size, PAGE_SIZE);
        unsigned long frames[pages];
        int f;

        /*
         * A GDT can be up to 64k in size, which corresponds to 8192
         * 8-byte entries, or 16 4k pages..
         */

        BUG_ON(size > 65536);
        BUG_ON(va & ~PAGE_MASK);

        for (f = 0; va < dtr->address + size; va += PAGE_SIZE, f++) {
                pte_t pte;
                unsigned long pfn, mfn;

                pfn = virt_to_pfn(va);
                mfn = pfn_to_mfn(pfn);

                pte = pfn_pte(pfn, PAGE_KERNEL_RO);

                if (HYPERVISOR_update_va_mapping((unsigned long)va, pte, 0))
                        BUG();

                frames[f] = mfn;
        }

        if (HYPERVISOR_set_gdt(frames, size / sizeof(struct desc_struct)))
                BUG();
}

static inline bool desc_equal(const struct desc_struct *d1,
                              const struct desc_struct *d2)
{
        return d1->a == d2->a && d1->b == d2->b;
}

static void load_TLS_descriptor(struct thread_struct *t,
                                unsigned int cpu, unsigned int i)
{
        struct desc_struct *shadow = &per_cpu(shadow_tls_desc, cpu).desc[i];
        struct desc_struct *gdt;
        xmaddr_t maddr;
        struct multicall_space mc;

        if (desc_equal(shadow, &t->tls_array[i]))
                return;

        *shadow = t->tls_array[i];

        gdt = get_cpu_gdt_rw(cpu);
        maddr = arbitrary_virt_to_machine(&gdt[GDT_ENTRY_TLS_MIN+i]);
        mc = __xen_mc_entry(0);

        MULTI_update_descriptor(mc.mc, maddr.maddr, t->tls_array[i]);
}

static void xen_load_tls(struct thread_struct *t, unsigned int cpu)
{
        /*
         * XXX sleazy hack: If we're being called in a lazy-cpu zone
         * and lazy gs handling is enabled, it means we're in a
         * context switch, and %gs has just been saved.  This means we
         * can zero it out to prevent faults on exit from the
         * hypervisor if the next process has no %gs.  Either way, it
         * has been saved, and the new value will get loaded properly.
         * This will go away as soon as Xen has been modified to not
         * save/restore %gs for normal hypercalls.
         *
         * On x86_64, this hack is not used for %gs, because gs points
         * to KERNEL_GS_BASE (and uses it for PDA references), so we
         * must not zero %gs on x86_64
         *
         * For x86_64, we need to zero %fs, otherwise we may get an
         * exception between the new %fs descriptor being loaded and
         * %fs being effectively cleared at __switch_to().
         */
        if (paravirt_get_lazy_mode() == PARAVIRT_LAZY_CPU) {
#ifdef CONFIG_X86_32
                lazy_load_gs(0);
#else
                loadsegment(fs, 0);
#endif
        }

        xen_mc_batch();

        load_TLS_descriptor(t, cpu, 0);
        load_TLS_descriptor(t, cpu, 1);
        load_TLS_descriptor(t, cpu, 2);

        xen_mc_issue(PARAVIRT_LAZY_CPU);
}

#ifdef CONFIG_X86_64
static void xen_load_gs_index(unsigned int idx)
{
        if (HYPERVISOR_set_segment_base(SEGBASE_GS_USER_SEL, idx))
                BUG();
}
#endif

static void xen_write_ldt_entry(struct desc_struct *dt, int entrynum,
                                const void *ptr)
{
        xmaddr_t mach_lp = arbitrary_virt_to_machine(&dt[entrynum]);
        u64 entry = *(u64 *)ptr;

        trace_xen_cpu_write_ldt_entry(dt, entrynum, entry);

        preempt_disable();

        xen_mc_flush();
        if (HYPERVISOR_update_descriptor(mach_lp.maddr, entry))
                BUG();

        preempt_enable();
}

static int cvt_gate_to_trap(int vector, const gate_desc *val,
                            struct trap_info *info)
{
        unsigned long addr;

        if (val->type != GATE_TRAP && val->type != GATE_INTERRUPT)
                return 0;

        info->vector = vector;

        addr = gate_offset(*val);
#ifdef CONFIG_X86_64
        /*
         * Look for known traps using IST, and substitute them
         * appropriately.  The debugger ones are the only ones we care
         * about.  Xen will handle faults like double_fault,
         * so we should never see them.  Warn if
         * there's an unexpected IST-using fault handler.
         */
        if (addr == (unsigned long)debug)
                addr = (unsigned long)xen_debug;
        else if (addr == (unsigned long)int3)
                addr = (unsigned long)xen_int3;
        else if (addr == (unsigned long)stack_segment)
                addr = (unsigned long)xen_stack_segment;
        else if (addr == (unsigned long)double_fault) {
                /* Don't need to handle these */
                return 0;
#ifdef CONFIG_X86_MCE
        } else if (addr == (unsigned long)machine_check) {
                /*
                 * when xen hypervisor inject vMCE to guest,
                 * use native mce handler to handle it
                 */
                ;
#endif
        } else if (addr == (unsigned long)nmi)
                /*
                 * Use the native version as well.
                 */
                ;
        else {
                /* Some other trap using IST? */
                if (WARN_ON(val->ist != 0))
                        return 0;
        }
#endif  /* CONFIG_X86_64 */
        info->address = addr;

        info->cs = gate_segment(*val);
        info->flags = val->dpl;
        /* interrupt gates clear IF */
        if (val->type == GATE_INTERRUPT)
                info->flags |= 1 << 2;

        return 1;
}

/* Locations of each CPU's IDT */
static DEFINE_PER_CPU(struct desc_ptr, idt_desc);

/* Set an IDT entry.  If the entry is part of the current IDT, then
   also update Xen. */
static void xen_write_idt_entry(gate_desc *dt, int entrynum, const gate_desc *g)
{
        unsigned long p = (unsigned long)&dt[entrynum];
        unsigned long start, end;

        trace_xen_cpu_write_idt_entry(dt, entrynum, g);

        preempt_disable();

        start = __this_cpu_read(idt_desc.address);
        end = start + __this_cpu_read(idt_desc.size) + 1;

        xen_mc_flush();

        native_write_idt_entry(dt, entrynum, g);

        if (p >= start && (p + 8) <= end) {
                struct trap_info info[2];

                info[1].address = 0;

                if (cvt_gate_to_trap(entrynum, g, &info[0]))
                        if (HYPERVISOR_set_trap_table(info))
                                BUG();
        }

        preempt_enable();
}

static void xen_convert_trap_info(const struct desc_ptr *desc,
                                  struct trap_info *traps)
{
        unsigned in, out, count;

        count = (desc->size+1) / sizeof(gate_desc);
        BUG_ON(count > 256);

        for (in = out = 0; in < count; in++) {
                gate_desc *entry = (gate_desc *)(desc->address) + in;

                if (cvt_gate_to_trap(in, entry, &traps[out]))
                        out++;
        }
        traps[out].address = 0;
}

void xen_copy_trap_info(struct trap_info *traps)
{
        const struct desc_ptr *desc = this_cpu_ptr(&idt_desc);

        xen_convert_trap_info(desc, traps);
}

/* Load a new IDT into Xen.  In principle this can be per-CPU, so we
   hold a spinlock to protect the static traps[] array (static because
   it avoids allocation, and saves stack space). */
static void xen_load_idt(const struct desc_ptr *desc)
{
        static DEFINE_SPINLOCK(lock);
        static struct trap_info traps[257];

        trace_xen_cpu_load_idt(desc);

        spin_lock(&lock);

        memcpy(this_cpu_ptr(&idt_desc), desc, sizeof(idt_desc));

        xen_convert_trap_info(desc, traps);

        xen_mc_flush();
        if (HYPERVISOR_set_trap_table(traps))
                BUG();

        spin_unlock(&lock);
}

/* Write a GDT descriptor entry.  Ignore LDT descriptors, since
   they're handled differently. */
static void xen_write_gdt_entry(struct desc_struct *dt, int entry,
                                const void *desc, int type)
{
        trace_xen_cpu_write_gdt_entry(dt, entry, desc, type);

        preempt_disable();

        switch (type) {
        case DESC_LDT:
        case DESC_TSS:
                /* ignore */
                break;

        default: {
                xmaddr_t maddr = arbitrary_virt_to_machine(&dt[entry]);

                xen_mc_flush();
                if (HYPERVISOR_update_descriptor(maddr.maddr, *(u64 *)desc))
                        BUG();
        }

        }

        preempt_enable();
}

/*
 * Version of write_gdt_entry for use at early boot-time needed to
 * update an entry as simply as possible.
 */
static void __init xen_write_gdt_entry_boot(struct desc_struct *dt, int entry,
                                            const void *desc, int type)
{
        trace_xen_cpu_write_gdt_entry(dt, entry, desc, type);

        switch (type) {
        case DESC_LDT:
        case DESC_TSS:
                /* ignore */
                break;

        default: {
                xmaddr_t maddr = virt_to_machine(&dt[entry]);

                if (HYPERVISOR_update_descriptor(maddr.maddr, *(u64 *)desc))
                        dt[entry] = *(struct desc_struct *)desc;
        }

        }
}

static void xen_load_sp0(struct tss_struct *tss,
                         struct thread_struct *thread)
{
        struct multicall_space mcs;

        mcs = xen_mc_entry(0);
        MULTI_stack_switch(mcs.mc, __KERNEL_DS, thread->sp0);
        xen_mc_issue(PARAVIRT_LAZY_CPU);
        tss->x86_tss.sp0 = thread->sp0;
}

void xen_set_iopl_mask(unsigned mask)
{
        struct physdev_set_iopl set_iopl;

        /* Force the change at ring 0. */
        set_iopl.iopl = (mask == 0) ? 1 : (mask >> 12) & 3;
        HYPERVISOR_physdev_op(PHYSDEVOP_set_iopl, &set_iopl);
}

static void xen_io_delay(void)
{
}

static DEFINE_PER_CPU(unsigned long, xen_cr0_value);

static unsigned long xen_read_cr0(void)
{
        unsigned long cr0 = this_cpu_read(xen_cr0_value);

        if (unlikely(cr0 == 0)) {
                cr0 = native_read_cr0();
                this_cpu_write(xen_cr0_value, cr0);
        }

        return cr0;
}

static void xen_write_cr0(unsigned long cr0)
{
        struct multicall_space mcs;

        this_cpu_write(xen_cr0_value, cr0);

        /* Only pay attention to cr0.TS; everything else is
           ignored. */
        mcs = xen_mc_entry(0);

        MULTI_fpu_taskswitch(mcs.mc, (cr0 & X86_CR0_TS) != 0);

        xen_mc_issue(PARAVIRT_LAZY_CPU);
}

static void xen_write_cr4(unsigned long cr4)
{
        cr4 &= ~(X86_CR4_PGE | X86_CR4_PSE | X86_CR4_PCE);

        native_write_cr4(cr4);
}
#ifdef CONFIG_X86_64
static inline unsigned long xen_read_cr8(void)
{
        return 0;
}
static inline void xen_write_cr8(unsigned long val)
{
        BUG_ON(val);
}
#endif

static u64 xen_read_msr_safe(unsigned int msr, int *err)
{
        u64 val;

        if (pmu_msr_read(msr, &val, err))
                return val;

        val = native_read_msr_safe(msr, err);
        switch (msr) {
        case MSR_IA32_APICBASE:
#ifdef CONFIG_X86_X2APIC
                if (!(cpuid_ecx(1) & (1 << (X86_FEATURE_X2APIC & 31))))
#endif
                        val &= ~X2APIC_ENABLE;
                break;
        }
        return val;
}

static int xen_write_msr_safe(unsigned int msr, unsigned low, unsigned high)
{
        int ret;

        ret = 0;

        switch (msr) {
#ifdef CONFIG_X86_64
                unsigned which;
                u64 base;

        case MSR_FS_BASE:               which = SEGBASE_FS; goto set;
        case MSR_KERNEL_GS_BASE:        which = SEGBASE_GS_USER; goto set;
        case MSR_GS_BASE:               which = SEGBASE_GS_KERNEL; goto set;

        set:
                base = ((u64)high << 32) | low;
                if (HYPERVISOR_set_segment_base(which, base) != 0)
                        ret = -EIO;
                break;
#endif

        case MSR_STAR:
        case MSR_CSTAR:
        case MSR_LSTAR:
        case MSR_SYSCALL_MASK:
        case MSR_IA32_SYSENTER_CS:
        case MSR_IA32_SYSENTER_ESP:
        case MSR_IA32_SYSENTER_EIP:
                /* Fast syscall setup is all done in hypercalls, so
                   these are all ignored.  Stub them out here to stop
                   Xen console noise. */
                break;

        default:
                if (!pmu_msr_write(msr, low, high, &ret))
                        ret = native_write_msr_safe(msr, low, high);
        }

        return ret;
}

static u64 xen_read_msr(unsigned int msr)
{
        /*
         * This will silently swallow a #GP from RDMSR.  It may be worth
         * changing that.
         */
        int err;

        return xen_read_msr_safe(msr, &err);
}

static void xen_write_msr(unsigned int msr, unsigned low, unsigned high)
{
        /*
         * This will silently swallow a #GP from WRMSR.  It may be worth
         * changing that.
         */
        xen_write_msr_safe(msr, low, high);
}

void xen_setup_shared_info(void)
{
        if (!xen_feature(XENFEAT_auto_translated_physmap)) {
                set_fixmap(FIX_PARAVIRT_BOOTMAP,
                           xen_start_info->shared_info);

                HYPERVISOR_shared_info =
                        (struct shared_info *)fix_to_virt(FIX_PARAVIRT_BOOTMAP);
        } else
                HYPERVISOR_shared_info =
                        (struct shared_info *)__va(xen_start_info->shared_info);

#ifndef CONFIG_SMP
        /* In UP this is as good a place as any to set up shared info */
        xen_setup_vcpu_info_placement();
#endif

        xen_setup_mfn_list_list();
}

/* This is called once we have the cpu_possible_mask */
void xen_setup_vcpu_info_placement(void)
{
        int cpu;

        for_each_possible_cpu(cpu) {
                /* Set up direct vCPU id mapping for PV guests. */
                per_cpu(xen_vcpu_id, cpu) = cpu;
                xen_vcpu_setup(cpu);
        }

        /*
         * xen_vcpu_setup managed to place the vcpu_info within the
         * percpu area for all cpus, so make use of it.
         */
        if (xen_have_vcpu_info_placement) {
                pv_irq_ops.save_fl = __PV_IS_CALLEE_SAVE(xen_save_fl_direct);
                pv_irq_ops.restore_fl = __PV_IS_CALLEE_SAVE(xen_restore_fl_direct);
                pv_irq_ops.irq_disable = __PV_IS_CALLEE_SAVE(xen_irq_disable_direct);
                pv_irq_ops.irq_enable = __PV_IS_CALLEE_SAVE(xen_irq_enable_direct);
                pv_mmu_ops.read_cr2 = xen_read_cr2_direct;
        }
}

static unsigned xen_patch(u8 type, u16 clobbers, void *insnbuf,
                          unsigned long addr, unsigned len)
{
        char *start, *end, *reloc;
        unsigned ret;

        start = end = reloc = NULL;

#define SITE(op, x)                                                     \
        case PARAVIRT_PATCH(op.x):                                      \
        if (xen_have_vcpu_info_placement) {                             \
                start = (char *)xen_##x##_direct;                       \
                end = xen_##x##_direct_end;                             \
                reloc = xen_##x##_direct_reloc;                         \
        }                                                               \
        goto patch_site

        switch (type) {
                SITE(pv_irq_ops, irq_enable);
                SITE(pv_irq_ops, irq_disable);
                SITE(pv_irq_ops, save_fl);
                SITE(pv_irq_ops, restore_fl);
#undef SITE

        patch_site:
                if (start == NULL || (end-start) > len)
                        goto default_patch;

                ret = paravirt_patch_insns(insnbuf, len, start, end);

                /* Note: because reloc is assigned from something that
                   appears to be an array, gcc assumes it's non-null,
                   but doesn't know its relationship with start and
                   end. */
                if (reloc > start && reloc < end) {
                        int reloc_off = reloc - start;
                        long *relocp = (long *)(insnbuf + reloc_off);
                        long delta = start - (char *)addr;

                        *relocp += delta;
                }
                break;

        default_patch:
        default:
                ret = paravirt_patch_default(type, clobbers, insnbuf,
                                             addr, len);
                break;
        }

        return ret;
}

static const struct pv_info xen_info __initconst = {
        .shared_kernel_pmd = 0,

#ifdef CONFIG_X86_64
        .extra_user_64bit_cs = FLAT_USER_CS64,
#endif
        .name = "Xen",
};

static const struct pv_init_ops xen_init_ops __initconst = {
        .patch = xen_patch,
};

static const struct pv_cpu_ops xen_cpu_ops __initconst = {
        .cpuid = xen_cpuid,

        .set_debugreg = xen_set_debugreg,
        .get_debugreg = xen_get_debugreg,

        .read_cr0 = xen_read_cr0,
        .write_cr0 = xen_write_cr0,

        .read_cr4 = native_read_cr4,
        .write_cr4 = xen_write_cr4,

#ifdef CONFIG_X86_64
        .read_cr8 = xen_read_cr8,
        .write_cr8 = xen_write_cr8,
#endif

        .wbinvd = native_wbinvd,

        .read_msr = xen_read_msr,
        .write_msr = xen_write_msr,

        .read_msr_safe = xen_read_msr_safe,
        .write_msr_safe = xen_write_msr_safe,

        .read_pmc = xen_read_pmc,

        .iret = xen_iret,
#ifdef CONFIG_X86_64
        .usergs_sysret64 = xen_sysret64,
#endif

        .load_tr_desc = paravirt_nop,
        .set_ldt = xen_set_ldt,
        .load_gdt = xen_load_gdt,
        .load_idt = xen_load_idt,
        .load_tls = xen_load_tls,
#ifdef CONFIG_X86_64
        .load_gs_index = xen_load_gs_index,
#endif

        .alloc_ldt = xen_alloc_ldt,
        .free_ldt = xen_free_ldt,

        .store_idt = native_store_idt,
        .store_tr = xen_store_tr,

        .write_ldt_entry = xen_write_ldt_entry,
        .write_gdt_entry = xen_write_gdt_entry,
        .write_idt_entry = xen_write_idt_entry,
        .load_sp0 = xen_load_sp0,

        .set_iopl_mask = xen_set_iopl_mask,
        .io_delay = xen_io_delay,

        /* Xen takes care of %gs when switching to usermode for us */
        .swapgs = paravirt_nop,

        .start_context_switch = paravirt_start_context_switch,
        .end_context_switch = xen_end_context_switch,
};

static void xen_restart(char *msg)
{
        xen_reboot(SHUTDOWN_reboot);
}

static void xen_machine_halt(void)
{
        xen_reboot(SHUTDOWN_poweroff);
}

static void xen_machine_power_off(void)
{
        if (pm_power_off)
                pm_power_off();
        xen_reboot(SHUTDOWN_poweroff);
}

static void xen_crash_shutdown(struct pt_regs *regs)
{
        xen_reboot(SHUTDOWN_crash);
}

static const struct machine_ops xen_machine_ops __initconst = {
        .restart = xen_restart,
        .halt = xen_machine_halt,
        .power_off = xen_machine_power_off,
        .shutdown = xen_machine_halt,
        .crash_shutdown = xen_crash_shutdown,
        .emergency_restart = xen_emergency_restart,
};

static unsigned char xen_get_nmi_reason(void)
{
        unsigned char reason = 0;

        /* Construct a value which looks like it came from port 0x61. */
        if (test_bit(_XEN_NMIREASON_io_error,
                     &HYPERVISOR_shared_info->arch.nmi_reason))
                reason |= NMI_REASON_IOCHK;
        if (test_bit(_XEN_NMIREASON_pci_serr,
                     &HYPERVISOR_shared_info->arch.nmi_reason))
                reason |= NMI_REASON_SERR;

        return reason;
}

static void __init xen_boot_params_init_edd(void)
{
#if IS_ENABLED(CONFIG_EDD)
        struct xen_platform_op op;
        struct edd_info *edd_info;
        u32 *mbr_signature;
        unsigned nr;
        int ret;

        edd_info = boot_params.eddbuf;
        mbr_signature = boot_params.edd_mbr_sig_buffer;

        op.cmd = XENPF_firmware_info;

        op.u.firmware_info.type = XEN_FW_DISK_INFO;
        for (nr = 0; nr < EDDMAXNR; nr++) {
                struct edd_info *info = edd_info + nr;

                op.u.firmware_info.index = nr;
                info->params.length = sizeof(info->params);
                set_xen_guest_handle(op.u.firmware_info.u.disk_info.edd_params,
                                     &info->params);
                ret = HYPERVISOR_platform_op(&op);
                if (ret)
                        break;

#define C(x) info->x = op.u.firmware_info.u.disk_info.x
                C(device);
                C(version);
                C(interface_support);
                C(legacy_max_cylinder);
                C(legacy_max_head);
                C(legacy_sectors_per_track);
#undef C
        }
        boot_params.eddbuf_entries = nr;

        op.u.firmware_info.type = XEN_FW_DISK_MBR_SIGNATURE;
        for (nr = 0; nr < EDD_MBR_SIG_MAX; nr++) {
                op.u.firmware_info.index = nr;
                ret = HYPERVISOR_platform_op(&op);
                if (ret)
                        break;
                mbr_signature[nr] = op.u.firmware_info.u.disk_mbr_signature.mbr_signature;
        }
        boot_params.edd_mbr_sig_buf_entries = nr;
#endif
}

/*
 * Set up the GDT and segment registers for -fstack-protector.  Until
 * we do this, we have to be careful not to call any stack-protected
 * function, which is most of the kernel.
 */
static void xen_setup_gdt(int cpu)
{
        pv_cpu_ops.write_gdt_entry = xen_write_gdt_entry_boot;
        pv_cpu_ops.load_gdt = xen_load_gdt_boot;

        setup_stack_canary_segment(0);
        switch_to_new_gdt(0);

        pv_cpu_ops.write_gdt_entry = xen_write_gdt_entry;
        pv_cpu_ops.load_gdt = xen_load_gdt;
}

static void __init xen_dom0_set_legacy_features(void)
{
        x86_platform.legacy.rtc = 1;
}

/* First C function to be called on Xen boot */
asmlinkage __visible void __init xen_start_kernel(void)
{
        struct physdev_set_iopl set_iopl;
        unsigned long initrd_start = 0;
        int rc;

        if (!xen_start_info)
                return;

        xen_domain_type = XEN_PV_DOMAIN;

        xen_setup_features();

        xen_setup_machphys_mapping();

        /* Install Xen paravirt ops */
        pv_info = xen_info;
        pv_init_ops = xen_init_ops;
        pv_cpu_ops = xen_cpu_ops;

        x86_platform.get_nmi_reason = xen_get_nmi_reason;

        x86_init.resources.memory_setup = xen_memory_setup;
        x86_init.oem.arch_setup = xen_arch_setup;
        x86_init.oem.banner = xen_banner;

        xen_init_time_ops();

        /*
         * Set up some pagetable state before starting to set any ptes.
         */

        xen_init_mmu_ops();

        /* Prevent unwanted bits from being set in PTEs. */
        __supported_pte_mask &= ~_PAGE_GLOBAL;

        /*
         * Prevent page tables from being allocated in highmem, even
         * if CONFIG_HIGHPTE is enabled.
         */
        __userpte_alloc_gfp &= ~__GFP_HIGHMEM;

        /* Work out if we support NX */
        x86_configure_nx();

        /* Get mfn list */
        xen_build_dynamic_phys_to_machine();

        /*
         * Set up kernel GDT and segment registers, mainly so that
         * -fstack-protector code can be executed.
         */
        xen_setup_gdt(0);

        xen_init_irq_ops();
        xen_init_capabilities();

#ifdef CONFIG_X86_LOCAL_APIC
        /*
         * set up the basic apic ops.
         */
        xen_init_apic();
#endif

        if (xen_feature(XENFEAT_mmu_pt_update_preserve_ad)) {
                pv_mmu_ops.ptep_modify_prot_start = xen_ptep_modify_prot_start;
                pv_mmu_ops.ptep_modify_prot_commit = xen_ptep_modify_prot_commit;
        }

        machine_ops = xen_machine_ops;

        /*
         * The only reliable way to retain the initial address of the
         * percpu gdt_page is to remember it here, so we can go and
         * mark it RW later, when the initial percpu area is freed.
         */
        xen_initial_gdt = &per_cpu(gdt_page, 0);

        xen_smp_init();

#ifdef CONFIG_ACPI_NUMA
        /*
         * The pages we from Xen are not related to machine pages, so
         * any NUMA information the kernel tries to get from ACPI will
         * be meaningless.  Prevent it from trying.
         */
        acpi_numa = -1;
#endif
        /* Don't do the full vcpu_info placement stuff until we have a
           possible map and a non-dummy shared_info. */
        per_cpu(xen_vcpu, 0) = &HYPERVISOR_shared_info->vcpu_info[0];

        WARN_ON(xen_cpuhp_setup(xen_cpu_up_prepare_pv, xen_cpu_dead_pv));

        local_irq_disable();
        early_boot_irqs_disabled = true;

        xen_raw_console_write("mapping kernel into physical memory\n");
        xen_setup_kernel_pagetable((pgd_t *)xen_start_info->pt_base,
                                   xen_start_info->nr_pages);
        xen_reserve_special_pages();

        /* keep using Xen gdt for now; no urgent need to change it */

#ifdef CONFIG_X86_32
        pv_info.kernel_rpl = 1;
        if (xen_feature(XENFEAT_supervisor_mode_kernel))
                pv_info.kernel_rpl = 0;
#else
        pv_info.kernel_rpl = 0;
#endif
        /* set the limit of our address space */
        xen_reserve_top();

        /*
         * We used to do this in xen_arch_setup, but that is too late
         * on AMD were early_cpu_init (run before ->arch_setup()) calls
         * early_amd_init which pokes 0xcf8 port.
         */
        set_iopl.iopl = 1;
        rc = HYPERVISOR_physdev_op(PHYSDEVOP_set_iopl, &set_iopl);
        if (rc != 0)
                xen_raw_printk("physdev_op failed %d\n", rc);

#ifdef CONFIG_X86_32
        /* set up basic CPUID stuff */
        cpu_detect(&new_cpu_data);
        set_cpu_cap(&new_cpu_data, X86_FEATURE_FPU);
        new_cpu_data.x86_capability[CPUID_1_EDX] = cpuid_edx(1);
#endif

        if (xen_start_info->mod_start) {
            if (xen_start_info->flags & SIF_MOD_START_PFN)
                initrd_start = PFN_PHYS(xen_start_info->mod_start);
            else
                initrd_start = __pa(xen_start_info->mod_start);
        }

        /* Poke various useful things into boot_params */
        boot_params.hdr.type_of_loader = (9 << 4) | 0;
        boot_params.hdr.ramdisk_image = initrd_start;
        boot_params.hdr.ramdisk_size = xen_start_info->mod_len;
        boot_params.hdr.cmd_line_ptr = __pa(xen_start_info->cmd_line);
        boot_params.hdr.hardware_subarch = X86_SUBARCH_XEN;

        if (!xen_initial_domain()) {
                add_preferred_console("xenboot", 0, NULL);
                add_preferred_console("tty", 0, NULL);
                add_preferred_console("hvc", 0, NULL);
                if (pci_xen)
                        x86_init.pci.arch_init = pci_xen_init;
        } else {
                const struct dom0_vga_console_info *info =
                        (void *)((char *)xen_start_info +
                                 xen_start_info->console.dom0.info_off);
                struct xen_platform_op op = {
                        .cmd = XENPF_firmware_info,
                        .interface_version = XENPF_INTERFACE_VERSION,
                        .u.firmware_info.type = XEN_FW_KBD_SHIFT_FLAGS,
                };

                x86_platform.set_legacy_features =
                                xen_dom0_set_legacy_features;
                xen_init_vga(info, xen_start_info->console.dom0.info_size);
                xen_start_info->console.domU.mfn = 0;
                xen_start_info->console.domU.evtchn = 0;

                if (HYPERVISOR_platform_op(&op) == 0)
                        boot_params.kbd_status = op.u.firmware_info.u.kbd_shift_flags;

                /* Make sure ACS will be enabled */
                pci_request_acs();

                xen_acpi_sleep_register();

                /* Avoid searching for BIOS MP tables */
                x86_init.mpparse.find_smp_config = x86_init_noop;
                x86_init.mpparse.get_smp_config = x86_init_uint_noop;

                xen_boot_params_init_edd();
        }
#ifdef CONFIG_PCI
        /* PCI BIOS service won't work from a PV guest. */
        pci_probe &= ~PCI_PROBE_BIOS;
#endif
        xen_raw_console_write("about to get started...\n");

        /* Let's presume PV guests always boot on vCPU with id 0. */
        per_cpu(xen_vcpu_id, 0) = 0;

        xen_setup_runstate_info(0);

        xen_efi_init();

        /* Start the world */
#ifdef CONFIG_X86_32
        i386_start_kernel();
#else
        cr4_init_shadow(); /* 32b kernel does this in i386_start_kernel() */
        x86_64_start_reservations((char *)__pa_symbol(&boot_params));
#endif
}

static int xen_cpu_up_prepare_pv(unsigned int cpu)
{
        int rc;

        xen_setup_timer(cpu);

        rc = xen_smp_intr_init(cpu);
        if (rc) {
                WARN(1, "xen_smp_intr_init() for CPU %d failed: %d\n",
                     cpu, rc);
                return rc;
        }

        rc = xen_smp_intr_init_pv(cpu);
        if (rc) {
                WARN(1, "xen_smp_intr_init_pv() for CPU %d failed: %d\n",
                     cpu, rc);
                return rc;
        }

        return 0;
}

static int xen_cpu_dead_pv(unsigned int cpu)
{
        xen_smp_intr_free(cpu);
        xen_smp_intr_free_pv(cpu);

        xen_teardown_timer(cpu);

        return 0;
}

static uint32_t __init xen_platform_pv(void)
{
        if (xen_pv_domain())
                return xen_cpuid_base();

        return 0;
}

const struct hypervisor_x86 x86_hyper_xen_pv = {
        .name                   = "Xen PV",
        .detect                 = xen_platform_pv,
        .pin_vcpu               = xen_pin_vcpu,
};
EXPORT_SYMBOL(x86_hyper_xen_pv);