x86/mm: Clarify the whole ASID/kernel PCID/user PCID naming

[mirror_ubuntu-bionic-kernel.git] / arch / x86 / include / asm / tlbflush.h

/* SPDX-License-Identifier: GPL-2.0 */
#ifndef _ASM_X86_TLBFLUSH_H
#define _ASM_X86_TLBFLUSH_H

#include <linux/mm.h>
#include <linux/sched.h>

#include <asm/processor.h>
#include <asm/cpufeature.h>
#include <asm/special_insns.h>
#include <asm/smp.h>
#include <asm/invpcid.h>
#include <asm/pti.h>
#include <asm/processor-flags.h>

/*
 * The x86 feature is called PCID (Process Context IDentifier). It is similar
 * to what is traditionally called ASID on the RISC processors.
 *
 * We don't use the traditional ASID implementation, where each process/mm gets
 * its own ASID and flush/restart when we run out of ASID space.
 *
 * Instead we have a small per-cpu array of ASIDs and cache the last few mm's
 * that came by on this CPU, allowing cheaper switch_mm between processes on
 * this CPU.
 *
 * We end up with different spaces for different things. To avoid confusion we
 * use different names for each of them:
 *
 * ASID  - [0, TLB_NR_DYN_ASIDS-1]
 *         the canonical identifier for an mm
 *
 * kPCID - [1, TLB_NR_DYN_ASIDS]
 *         the value we write into the PCID part of CR3; corresponds to the
 *         ASID+1, because PCID 0 is special.
 *
 * uPCID - [2048 + 1, 2048 + TLB_NR_DYN_ASIDS]
 *         for KPTI each mm has two address spaces and thus needs two
 *         PCID values, but we can still do with a single ASID denomination
 *         for each mm. Corresponds to kPCID + 2048.
 *
 */

/* There are 12 bits of space for ASIDS in CR3 */
#define CR3_HW_ASID_BITS                12

/*
 * When enabled, PAGE_TABLE_ISOLATION consumes a single bit for
 * user/kernel switches
 */
#ifdef CONFIG_PAGE_TABLE_ISOLATION
# define PTI_CONSUMED_PCID_BITS 1
#else
# define PTI_CONSUMED_PCID_BITS 0
#endif

#define CR3_AVAIL_PCID_BITS (X86_CR3_PCID_BITS - PTI_CONSUMED_PCID_BITS)

/*
 * ASIDs are zero-based: 0->MAX_AVAIL_ASID are valid.  -1 below to account
 * for them being zero-based.  Another -1 is because PCID 0 is reserved for
 * use by non-PCID-aware users.
 */
#define MAX_ASID_AVAILABLE ((1 << CR3_AVAIL_PCID_BITS) - 2)

/*
 * 6 because 6 should be plenty and struct tlb_state will fit in two cache
 * lines.
 */
#define TLB_NR_DYN_ASIDS        6

/*
 * Given @asid, compute kPCID
 */
static inline u16 kern_pcid(u16 asid)
{
        VM_WARN_ON_ONCE(asid > MAX_ASID_AVAILABLE);

#ifdef CONFIG_PAGE_TABLE_ISOLATION
        /*
         * Make sure that the dynamic ASID space does not confict with the
         * bit we are using to switch between user and kernel ASIDs.
         */
        BUILD_BUG_ON(TLB_NR_DYN_ASIDS >= (1 << X86_CR3_PTI_SWITCH_BIT));

        /*
         * The ASID being passed in here should have respected the
         * MAX_ASID_AVAILABLE and thus never have the switch bit set.
         */
        VM_WARN_ON_ONCE(asid & (1 << X86_CR3_PTI_SWITCH_BIT));
#endif
        /*
         * The dynamically-assigned ASIDs that get passed in are small
         * (<TLB_NR_DYN_ASIDS).  They never have the high switch bit set,
         * so do not bother to clear it.
         *
         * If PCID is on, ASID-aware code paths put the ASID+1 into the
         * PCID bits.  This serves two purposes.  It prevents a nasty
         * situation in which PCID-unaware code saves CR3, loads some other
         * value (with PCID == 0), and then restores CR3, thus corrupting
         * the TLB for ASID 0 if the saved ASID was nonzero.  It also means
         * that any bugs involving loading a PCID-enabled CR3 with
         * CR4.PCIDE off will trigger deterministically.
         */
        return asid + 1;
}

/*
 * Given @asid, compute uPCID
 */
static inline u16 user_pcid(u16 asid)
{
        u16 ret = kern_pcid(asid);
#ifdef CONFIG_PAGE_TABLE_ISOLATION
        ret |= 1 << X86_CR3_PTI_SWITCH_BIT;
#endif
        return ret;
}

struct pgd_t;
static inline unsigned long build_cr3(pgd_t *pgd, u16 asid)
{
        if (static_cpu_has(X86_FEATURE_PCID)) {
                return __sme_pa(pgd) | kern_pcid(asid);
        } else {
                VM_WARN_ON_ONCE(asid != 0);
                return __sme_pa(pgd);
        }
}

static inline unsigned long build_cr3_noflush(pgd_t *pgd, u16 asid)
{
        VM_WARN_ON_ONCE(asid > MAX_ASID_AVAILABLE);
        VM_WARN_ON_ONCE(!this_cpu_has(X86_FEATURE_PCID));
        return __sme_pa(pgd) | kern_pcid(asid) | CR3_NOFLUSH;
}

#ifdef CONFIG_PARAVIRT
#include <asm/paravirt.h>
#else
#define __flush_tlb() __native_flush_tlb()
#define __flush_tlb_global() __native_flush_tlb_global()
#define __flush_tlb_single(addr) __native_flush_tlb_single(addr)
#endif

static inline bool tlb_defer_switch_to_init_mm(void)
{
        /*
         * If we have PCID, then switching to init_mm is reasonably
         * fast.  If we don't have PCID, then switching to init_mm is
         * quite slow, so we try to defer it in the hopes that we can
         * avoid it entirely.  The latter approach runs the risk of
         * receiving otherwise unnecessary IPIs.
         *
         * This choice is just a heuristic.  The tlb code can handle this
         * function returning true or false regardless of whether we have
         * PCID.
         */
        return !static_cpu_has(X86_FEATURE_PCID);
}

struct tlb_context {
        u64 ctx_id;
        u64 tlb_gen;
};

struct tlb_state {
        /*
         * cpu_tlbstate.loaded_mm should match CR3 whenever interrupts
         * are on.  This means that it may not match current->active_mm,
         * which will contain the previous user mm when we're in lazy TLB
         * mode even if we've already switched back to swapper_pg_dir.
         */
        struct mm_struct *loaded_mm;
        u16 loaded_mm_asid;
        u16 next_asid;

        /*
         * We can be in one of several states:
         *
         *  - Actively using an mm.  Our CPU's bit will be set in
         *    mm_cpumask(loaded_mm) and is_lazy == false;
         *
         *  - Not using a real mm.  loaded_mm == &init_mm.  Our CPU's bit
         *    will not be set in mm_cpumask(&init_mm) and is_lazy == false.
         *
         *  - Lazily using a real mm.  loaded_mm != &init_mm, our bit
         *    is set in mm_cpumask(loaded_mm), but is_lazy == true.
         *    We're heuristically guessing that the CR3 load we
         *    skipped more than makes up for the overhead added by
         *    lazy mode.
         */
        bool is_lazy;

        /*
         * If set we changed the page tables in such a way that we
         * needed an invalidation of all contexts (aka. PCIDs / ASIDs).
         * This tells us to go invalidate all the non-loaded ctxs[]
         * on the next context switch.
         *
         * The current ctx was kept up-to-date as it ran and does not
         * need to be invalidated.
         */
        bool invalidate_other;

        /*
         * Mask that contains TLB_NR_DYN_ASIDS+1 bits to indicate
         * the corresponding user PCID needs a flush next time we
         * switch to it; see SWITCH_TO_USER_CR3.
         */
        unsigned short user_pcid_flush_mask;

        /*
         * Access to this CR4 shadow and to H/W CR4 is protected by
         * disabling interrupts when modifying either one.
         */
        unsigned long cr4;

        /*
         * This is a list of all contexts that might exist in the TLB.
         * There is one per ASID that we use, and the ASID (what the
         * CPU calls PCID) is the index into ctxts.
         *
         * For each context, ctx_id indicates which mm the TLB's user
         * entries came from.  As an invariant, the TLB will never
         * contain entries that are out-of-date as when that mm reached
         * the tlb_gen in the list.
         *
         * To be clear, this means that it's legal for the TLB code to
         * flush the TLB without updating tlb_gen.  This can happen
         * (for now, at least) due to paravirt remote flushes.
         *
         * NB: context 0 is a bit special, since it's also used by
         * various bits of init code.  This is fine -- code that
         * isn't aware of PCID will end up harmlessly flushing
         * context 0.
         */
        struct tlb_context ctxs[TLB_NR_DYN_ASIDS];
};
DECLARE_PER_CPU_SHARED_ALIGNED(struct tlb_state, cpu_tlbstate);

/* Initialize cr4 shadow for this CPU. */
static inline void cr4_init_shadow(void)
{
        this_cpu_write(cpu_tlbstate.cr4, __read_cr4());
}

/* Set in this cpu's CR4. */
static inline void cr4_set_bits(unsigned long mask)
{
        unsigned long cr4;

        cr4 = this_cpu_read(cpu_tlbstate.cr4);
        if ((cr4 | mask) != cr4) {
                cr4 |= mask;
                this_cpu_write(cpu_tlbstate.cr4, cr4);
                __write_cr4(cr4);
        }
}

/* Clear in this cpu's CR4. */
static inline void cr4_clear_bits(unsigned long mask)
{
        unsigned long cr4;

        cr4 = this_cpu_read(cpu_tlbstate.cr4);
        if ((cr4 & ~mask) != cr4) {
                cr4 &= ~mask;
                this_cpu_write(cpu_tlbstate.cr4, cr4);
                __write_cr4(cr4);
        }
}

static inline void cr4_toggle_bits(unsigned long mask)
{
        unsigned long cr4;

        cr4 = this_cpu_read(cpu_tlbstate.cr4);
        cr4 ^= mask;
        this_cpu_write(cpu_tlbstate.cr4, cr4);
        __write_cr4(cr4);
}

/* Read the CR4 shadow. */
static inline unsigned long cr4_read_shadow(void)
{
        return this_cpu_read(cpu_tlbstate.cr4);
}

/*
 * Mark all other ASIDs as invalid, preserves the current.
 */
static inline void invalidate_other_asid(void)
{
        this_cpu_write(cpu_tlbstate.invalidate_other, true);
}

/*
 * Save some of cr4 feature set we're using (e.g.  Pentium 4MB
 * enable and PPro Global page enable), so that any CPU's that boot
 * up after us can get the correct flags.  This should only be used
 * during boot on the boot cpu.
 */
extern unsigned long mmu_cr4_features;
extern u32 *trampoline_cr4_features;

static inline void cr4_set_bits_and_update_boot(unsigned long mask)
{
        mmu_cr4_features |= mask;
        if (trampoline_cr4_features)
                *trampoline_cr4_features = mmu_cr4_features;
        cr4_set_bits(mask);
}

extern void initialize_tlbstate_and_flush(void);

/*
 * Given an ASID, flush the corresponding user ASID.  We can delay this
 * until the next time we switch to it.
 *
 * See SWITCH_TO_USER_CR3.
 */
static inline void invalidate_user_asid(u16 asid)
{
        /* There is no user ASID if address space separation is off */
        if (!IS_ENABLED(CONFIG_PAGE_TABLE_ISOLATION))
                return;

        /*
         * We only have a single ASID if PCID is off and the CR3
         * write will have flushed it.
         */
        if (!cpu_feature_enabled(X86_FEATURE_PCID))
                return;

        if (!static_cpu_has(X86_FEATURE_PTI))
                return;

        __set_bit(kern_pcid(asid),
                  (unsigned long *)this_cpu_ptr(&cpu_tlbstate.user_pcid_flush_mask));
}

/*
 * flush the entire current user mapping
 */
static inline void __native_flush_tlb(void)
{
        invalidate_user_asid(this_cpu_read(cpu_tlbstate.loaded_mm_asid));
        /*
         * If current->mm == NULL then we borrow a mm which may change
         * during a task switch and therefore we must not be preempted
         * while we write CR3 back:
         */
        preempt_disable();
        native_write_cr3(__native_read_cr3());
        preempt_enable();
}

/*
 * flush everything
 */
static inline void __native_flush_tlb_global(void)
{
        unsigned long cr4, flags;

        if (static_cpu_has(X86_FEATURE_INVPCID)) {
                /*
                 * Using INVPCID is considerably faster than a pair of writes
                 * to CR4 sandwiched inside an IRQ flag save/restore.
                 *
                 * Note, this works with CR4.PCIDE=0 or 1.
                 */
                invpcid_flush_all();
                return;
        }

        /*
         * Read-modify-write to CR4 - protect it from preemption and
         * from interrupts. (Use the raw variant because this code can
         * be called from deep inside debugging code.)
         */
        raw_local_irq_save(flags);

        cr4 = this_cpu_read(cpu_tlbstate.cr4);
        /* toggle PGE */
        native_write_cr4(cr4 ^ X86_CR4_PGE);
        /* write old PGE again and flush TLBs */
        native_write_cr4(cr4);

        raw_local_irq_restore(flags);
}

/*
 * flush one page in the user mapping
 */
static inline void __native_flush_tlb_single(unsigned long addr)
{
        u32 loaded_mm_asid = this_cpu_read(cpu_tlbstate.loaded_mm_asid);

        asm volatile("invlpg (%0)" ::"r" (addr) : "memory");

        if (!static_cpu_has(X86_FEATURE_PTI))
                return;

        /*
         * Some platforms #GP if we call invpcid(type=1/2) before CR4.PCIDE=1.
         * Just use invalidate_user_asid() in case we are called early.
         */
        if (!this_cpu_has(X86_FEATURE_INVPCID_SINGLE))
                invalidate_user_asid(loaded_mm_asid);
        else
                invpcid_flush_one(user_pcid(loaded_mm_asid), addr);
}

/*
 * flush everything
 */
static inline void __flush_tlb_all(void)
{
        if (boot_cpu_has(X86_FEATURE_PGE)) {
                __flush_tlb_global();
        } else {
                /*
                 * !PGE -> !PCID (setup_pcid()), thus every flush is total.
                 */
                __flush_tlb();
        }
}

/*
 * flush one page in the kernel mapping
 */
static inline void __flush_tlb_one(unsigned long addr)
{
        count_vm_tlb_event(NR_TLB_LOCAL_FLUSH_ONE);
        __flush_tlb_single(addr);

        if (!static_cpu_has(X86_FEATURE_PTI))
                return;

        /*
         * __flush_tlb_single() will have cleared the TLB entry for this ASID,
         * but since kernel space is replicated across all, we must also
         * invalidate all others.
         */
        invalidate_other_asid();
}

#define TLB_FLUSH_ALL   -1UL

/*
 * TLB flushing:
 *
 *  - flush_tlb_all() flushes all processes TLBs
 *  - flush_tlb_mm(mm) flushes the specified mm context TLB's
 *  - flush_tlb_page(vma, vmaddr) flushes one page
 *  - flush_tlb_range(vma, start, end) flushes a range of pages
 *  - flush_tlb_kernel_range(start, end) flushes a range of kernel pages
 *  - flush_tlb_others(cpumask, info) flushes TLBs on other cpus
 *
 * ..but the i386 has somewhat limited tlb flushing capabilities,
 * and page-granular flushes are available only on i486 and up.
 */
struct flush_tlb_info {
        /*
         * We support several kinds of flushes.
         *
         * - Fully flush a single mm.  .mm will be set, .end will be
         *   TLB_FLUSH_ALL, and .new_tlb_gen will be the tlb_gen to
         *   which the IPI sender is trying to catch us up.
         *
         * - Partially flush a single mm.  .mm will be set, .start and
         *   .end will indicate the range, and .new_tlb_gen will be set
         *   such that the changes between generation .new_tlb_gen-1 and
         *   .new_tlb_gen are entirely contained in the indicated range.
         *
         * - Fully flush all mms whose tlb_gens have been updated.  .mm
         *   will be NULL, .end will be TLB_FLUSH_ALL, and .new_tlb_gen
         *   will be zero.
         */
        struct mm_struct        *mm;
        unsigned long           start;
        unsigned long           end;
        u64                     new_tlb_gen;
};

#define local_flush_tlb() __flush_tlb()

#define flush_tlb_mm(mm)        flush_tlb_mm_range(mm, 0UL, TLB_FLUSH_ALL, 0UL)

#define flush_tlb_range(vma, start, end)        \
                flush_tlb_mm_range(vma->vm_mm, start, end, vma->vm_flags)

extern void flush_tlb_all(void);
extern void flush_tlb_mm_range(struct mm_struct *mm, unsigned long start,
                                unsigned long end, unsigned long vmflag);
extern void flush_tlb_kernel_range(unsigned long start, unsigned long end);

static inline void flush_tlb_page(struct vm_area_struct *vma, unsigned long a)
{
        flush_tlb_mm_range(vma->vm_mm, a, a + PAGE_SIZE, VM_NONE);
}

void native_flush_tlb_others(const struct cpumask *cpumask,
                             const struct flush_tlb_info *info);

static inline u64 inc_mm_tlb_gen(struct mm_struct *mm)
{
        /*
         * Bump the generation count.  This also serves as a full barrier
         * that synchronizes with switch_mm(): callers are required to order
         * their read of mm_cpumask after their writes to the paging
         * structures.
         */
        return atomic64_inc_return(&mm->context.tlb_gen);
}

static inline void arch_tlbbatch_add_mm(struct arch_tlbflush_unmap_batch *batch,
                                        struct mm_struct *mm)
{
        inc_mm_tlb_gen(mm);
        cpumask_or(&batch->cpumask, &batch->cpumask, mm_cpumask(mm));
}

extern void arch_tlbbatch_flush(struct arch_tlbflush_unmap_batch *batch);

#ifndef CONFIG_PARAVIRT
#define flush_tlb_others(mask, info)    \
        native_flush_tlb_others(mask, info)
#endif

#endif /* _ASM_X86_TLBFLUSH_H */