KVM: s390: vsie: support setting the ibc

[mirror_ubuntu-artful-kernel.git] / arch / s390 / kvm / vsie.c

/*
 * kvm nested virtualization support for s390x
 *
 * Copyright IBM Corp. 2016
 *
 * This program is free software; you can redistribute it and/or modify
 * it under the terms of the GNU General Public License (version 2 only)
 * as published by the Free Software Foundation.
 *
 *    Author(s): David Hildenbrand <dahi@linux.vnet.ibm.com>
 */
#include <linux/vmalloc.h>
#include <linux/kvm_host.h>
#include <linux/bug.h>
#include <linux/list.h>
#include <linux/bitmap.h>
#include <asm/gmap.h>
#include <asm/mmu_context.h>
#include <asm/sclp.h>
#include <asm/nmi.h>
#include "kvm-s390.h"
#include "gaccess.h"

struct vsie_page {
        struct kvm_s390_sie_block scb_s;        /* 0x0000 */
        /* the pinned originial scb */
        struct kvm_s390_sie_block *scb_o;       /* 0x0200 */
        /* the shadow gmap in use by the vsie_page */
        struct gmap *gmap;                      /* 0x0208 */
        __u8 reserved[0x1000 - 0x0210];         /* 0x0210 */
} __packed;

/* trigger a validity icpt for the given scb */
static int set_validity_icpt(struct kvm_s390_sie_block *scb,
                             __u16 reason_code)
{
        scb->ipa = 0x1000;
        scb->ipb = ((__u32) reason_code) << 16;
        scb->icptcode = ICPT_VALIDITY;
        return 1;
}

/* mark the prefix as unmapped, this will block the VSIE */
static void prefix_unmapped(struct vsie_page *vsie_page)
{
        atomic_or(PROG_REQUEST, &vsie_page->scb_s.prog20);
}

/* mark the prefix as unmapped and wait until the VSIE has been left */
static void prefix_unmapped_sync(struct vsie_page *vsie_page)
{
        prefix_unmapped(vsie_page);
        if (vsie_page->scb_s.prog0c & PROG_IN_SIE)
                atomic_or(CPUSTAT_STOP_INT, &vsie_page->scb_s.cpuflags);
        while (vsie_page->scb_s.prog0c & PROG_IN_SIE)
                cpu_relax();
}

/* mark the prefix as mapped, this will allow the VSIE to run */
static void prefix_mapped(struct vsie_page *vsie_page)
{
        atomic_andnot(PROG_REQUEST, &vsie_page->scb_s.prog20);
}

/* test if the prefix is mapped into the gmap shadow */
static int prefix_is_mapped(struct vsie_page *vsie_page)
{
        return !(atomic_read(&vsie_page->scb_s.prog20) & PROG_REQUEST);
}

/* copy the updated intervention request bits into the shadow scb */
static void update_intervention_requests(struct vsie_page *vsie_page)
{
        const int bits = CPUSTAT_STOP_INT | CPUSTAT_IO_INT | CPUSTAT_EXT_INT;
        int cpuflags;

        cpuflags = atomic_read(&vsie_page->scb_o->cpuflags);
        atomic_andnot(bits, &vsie_page->scb_s.cpuflags);
        atomic_or(cpuflags & bits, &vsie_page->scb_s.cpuflags);
}

/* shadow (filter and validate) the cpuflags  */
static int prepare_cpuflags(struct kvm_vcpu *vcpu, struct vsie_page *vsie_page)
{
        struct kvm_s390_sie_block *scb_s = &vsie_page->scb_s;
        struct kvm_s390_sie_block *scb_o = vsie_page->scb_o;
        int newflags, cpuflags = atomic_read(&scb_o->cpuflags);

        /* we don't allow ESA/390 guests */
        if (!(cpuflags & CPUSTAT_ZARCH))
                return set_validity_icpt(scb_s, 0x0001U);

        if (cpuflags & (CPUSTAT_RRF | CPUSTAT_MCDS))
                return set_validity_icpt(scb_s, 0x0001U);
        else if (cpuflags & (CPUSTAT_SLSV | CPUSTAT_SLSR))
                return set_validity_icpt(scb_s, 0x0007U);

        /* intervention requests will be set later */
        newflags = CPUSTAT_ZARCH;

        atomic_set(&scb_s->cpuflags, newflags);
        return 0;
}

/* shadow (round up/down) the ibc to avoid validity icpt */
static void prepare_ibc(struct kvm_vcpu *vcpu, struct vsie_page *vsie_page)
{
        struct kvm_s390_sie_block *scb_s = &vsie_page->scb_s;
        struct kvm_s390_sie_block *scb_o = vsie_page->scb_o;
        __u64 min_ibc = (sclp.ibc >> 16) & 0x0fffU;

        scb_s->ibc = 0;
        /* ibc installed in g2 and requested for g3 */
        if (vcpu->kvm->arch.model.ibc && (scb_o->ibc & 0x0fffU)) {
                scb_s->ibc = scb_o->ibc & 0x0fffU;
                /* takte care of the minimum ibc level of the machine */
                if (scb_s->ibc < min_ibc)
                        scb_s->ibc = min_ibc;
                /* take care of the maximum ibc level set for the guest */
                if (scb_s->ibc > vcpu->kvm->arch.model.ibc)
                        scb_s->ibc = vcpu->kvm->arch.model.ibc;
        }
}

/* unshadow the scb, copying parameters back to the real scb */
static void unshadow_scb(struct kvm_vcpu *vcpu, struct vsie_page *vsie_page)
{
        struct kvm_s390_sie_block *scb_s = &vsie_page->scb_s;
        struct kvm_s390_sie_block *scb_o = vsie_page->scb_o;

        /* interception */
        scb_o->icptcode = scb_s->icptcode;
        scb_o->icptstatus = scb_s->icptstatus;
        scb_o->ipa = scb_s->ipa;
        scb_o->ipb = scb_s->ipb;
        scb_o->gbea = scb_s->gbea;

        /* timer */
        scb_o->cputm = scb_s->cputm;
        scb_o->ckc = scb_s->ckc;
        scb_o->todpr = scb_s->todpr;

        /* guest state */
        scb_o->gpsw = scb_s->gpsw;
        scb_o->gg14 = scb_s->gg14;
        scb_o->gg15 = scb_s->gg15;
        memcpy(scb_o->gcr, scb_s->gcr, 128);
        scb_o->pp = scb_s->pp;

        /* interrupt intercept */
        switch (scb_s->icptcode) {
        case ICPT_PROGI:
        case ICPT_INSTPROGI:
        case ICPT_EXTINT:
                memcpy((void *)((u64)scb_o + 0xc0),
                       (void *)((u64)scb_s + 0xc0), 0xf0 - 0xc0);
                break;
        case ICPT_PARTEXEC:
                /* MVPG only */
                memcpy((void *)((u64)scb_o + 0xc0),
                       (void *)((u64)scb_s + 0xc0), 0xd0 - 0xc0);
                break;
        }

        if (scb_s->ihcpu != 0xffffU)
                scb_o->ihcpu = scb_s->ihcpu;
}

/*
 * Setup the shadow scb by copying and checking the relevant parts of the g2
 * provided scb.
 *
 * Returns: - 0 if the scb has been shadowed
 *          - > 0 if control has to be given to guest 2
 */
static int shadow_scb(struct kvm_vcpu *vcpu, struct vsie_page *vsie_page)
{
        struct kvm_s390_sie_block *scb_o = vsie_page->scb_o;
        struct kvm_s390_sie_block *scb_s = &vsie_page->scb_s;
        unsigned long new_mso;
        int rc;

        /* make sure we don't have any leftovers when reusing the scb */
        scb_s->icptcode = 0;
        scb_s->eca = 0;
        scb_s->ecb = 0;
        scb_s->ecb2 = 0;
        scb_s->ecb3 = 0;
        scb_s->ecd = 0;

        rc = prepare_cpuflags(vcpu, vsie_page);
        if (rc)
                goto out;

        /* timer */
        scb_s->cputm = scb_o->cputm;
        scb_s->ckc = scb_o->ckc;
        scb_s->todpr = scb_o->todpr;
        scb_s->epoch = scb_o->epoch;

        /* guest state */
        scb_s->gpsw = scb_o->gpsw;
        scb_s->gg14 = scb_o->gg14;
        scb_s->gg15 = scb_o->gg15;
        memcpy(scb_s->gcr, scb_o->gcr, 128);
        scb_s->pp = scb_o->pp;

        /* interception / execution handling */
        scb_s->gbea = scb_o->gbea;
        scb_s->lctl = scb_o->lctl;
        scb_s->svcc = scb_o->svcc;
        scb_s->ictl = scb_o->ictl;
        /*
         * SKEY handling functions can't deal with false setting of PTE invalid
         * bits. Therefore we cannot provide interpretation and would later
         * have to provide own emulation handlers.
         */
        scb_s->ictl |= ICTL_ISKE | ICTL_SSKE | ICTL_RRBE;
        scb_s->icpua = scb_o->icpua;

        new_mso = scb_o->mso & 0xfffffffffff00000UL;
        /* if the hva of the prefix changes, we have to remap the prefix */
        if (scb_s->mso != new_mso || scb_s->prefix != scb_o->prefix)
                prefix_unmapped(vsie_page);
         /* SIE will do mso/msl validity and exception checks for us */
        scb_s->msl = scb_o->msl & 0xfffffffffff00000UL;
        scb_s->mso = new_mso;
        scb_s->prefix = scb_o->prefix;

        /* We have to definetly flush the tlb if this scb never ran */
        if (scb_s->ihcpu != 0xffffU)
                scb_s->ihcpu = scb_o->ihcpu;

        /* MVPG and Protection Exception Interpretation are always available */
        scb_s->eca |= scb_o->eca & 0x01002000U;

        prepare_ibc(vcpu, vsie_page);
out:
        if (rc)
                unshadow_scb(vcpu, vsie_page);
        return rc;
}

void kvm_s390_vsie_gmap_notifier(struct gmap *gmap, unsigned long start,
                                 unsigned long end)
{
        struct kvm *kvm = gmap->private;
        struct vsie_page *cur;
        unsigned long prefix;
        struct page *page;
        int i;

        if (!gmap_is_shadow(gmap))
                return;
        if (start >= 1UL << 31)
                /* We are only interested in prefix pages */
                return;

        /*
         * Only new shadow blocks are added to the list during runtime,
         * therefore we can safely reference them all the time.
         */
        for (i = 0; i < kvm->arch.vsie.page_count; i++) {
                page = READ_ONCE(kvm->arch.vsie.pages[i]);
                if (!page)
                        continue;
                cur = page_to_virt(page);
                if (READ_ONCE(cur->gmap) != gmap)
                        continue;
                prefix = cur->scb_s.prefix << GUEST_PREFIX_SHIFT;
                /* with mso/msl, the prefix lies at an offset */
                prefix += cur->scb_s.mso;
                if (prefix <= end && start <= prefix + PAGE_SIZE - 1)
                        prefix_unmapped_sync(cur);
        }
}

/*
 * Map the first prefix page.
 *
 * The prefix will be protected, a gmap notifier will inform about unmaps.
 * The shadow scb must not be executed until the prefix is remapped, this is
 * guaranteed by properly handling PROG_REQUEST.
 *
 * Returns: - 0 on if successfully mapped or already mapped
 *          - > 0 if control has to be given to guest 2
 *          - -EAGAIN if the caller can retry immediately
 *          - -ENOMEM if out of memory
 */
static int map_prefix(struct kvm_vcpu *vcpu, struct vsie_page *vsie_page)
{
        struct kvm_s390_sie_block *scb_s = &vsie_page->scb_s;
        u64 prefix = scb_s->prefix << GUEST_PREFIX_SHIFT;
        int rc;

        if (prefix_is_mapped(vsie_page))
                return 0;

        /* mark it as mapped so we can catch any concurrent unmappers */
        prefix_mapped(vsie_page);

        /* with mso/msl, the prefix lies at offset *mso* */
        prefix += scb_s->mso;

        rc = kvm_s390_shadow_fault(vcpu, vsie_page->gmap, prefix);
        /*
         * We don't have to mprotect, we will be called for all unshadows.
         * SIE will detect if protection applies and trigger a validity.
         */
        if (rc)
                prefix_unmapped(vsie_page);
        if (rc > 0 || rc == -EFAULT)
                rc = set_validity_icpt(scb_s, 0x0037U);
        return rc;
}

/*
 * Pin the guest page given by gpa and set hpa to the pinned host address.
 * Will always be pinned writable.
 *
 * Returns: - 0 on success
 *          - -EINVAL if the gpa is not valid guest storage
 *          - -ENOMEM if out of memory
 */
static int pin_guest_page(struct kvm *kvm, gpa_t gpa, hpa_t *hpa)
{
        struct page *page;
        hva_t hva;
        int rc;

        hva = gfn_to_hva(kvm, gpa_to_gfn(gpa));
        if (kvm_is_error_hva(hva))
                return -EINVAL;
        rc = get_user_pages_fast(hva, 1, 1, &page);
        if (rc < 0)
                return rc;
        else if (rc != 1)
                return -ENOMEM;
        *hpa = (hpa_t) page_to_virt(page) + (gpa & ~PAGE_MASK);
        return 0;
}

/* Unpins a page previously pinned via pin_guest_page, marking it as dirty. */
static void unpin_guest_page(struct kvm *kvm, gpa_t gpa, hpa_t hpa)
{
        struct page *page;

        page = virt_to_page(hpa);
        set_page_dirty_lock(page);
        put_page(page);
        /* mark the page always as dirty for migration */
        mark_page_dirty(kvm, gpa_to_gfn(gpa));
}

/* unpin all blocks previously pinned by pin_blocks(), marking them dirty */
static void unpin_blocks(struct kvm_vcpu *vcpu, struct vsie_page *vsie_page)
{
        struct kvm_s390_sie_block *scb_o = vsie_page->scb_o;
        struct kvm_s390_sie_block *scb_s = &vsie_page->scb_s;
        hpa_t hpa;
        gpa_t gpa;

        hpa = (u64) scb_s->scaoh << 32 | scb_s->scaol;
        if (hpa) {
                gpa = scb_o->scaol & ~0xfUL;
                unpin_guest_page(vcpu->kvm, gpa, hpa);
                scb_s->scaol = 0;
                scb_s->scaoh = 0;
        }
}

/*
 * Instead of shadowing some blocks, we can simply forward them because the
 * addresses in the scb are 64 bit long.
 *
 * This works as long as the data lies in one page. If blocks ever exceed one
 * page, we have to fall back to shadowing.
 *
 * As we reuse the sca, the vcpu pointers contained in it are invalid. We must
 * therefore not enable any facilities that access these pointers (e.g. SIGPIF).
 *
 * Returns: - 0 if all blocks were pinned.
 *          - > 0 if control has to be given to guest 2
 *          - -ENOMEM if out of memory
 */
static int pin_blocks(struct kvm_vcpu *vcpu, struct vsie_page *vsie_page)
{
        struct kvm_s390_sie_block *scb_o = vsie_page->scb_o;
        struct kvm_s390_sie_block *scb_s = &vsie_page->scb_s;
        hpa_t hpa;
        gpa_t gpa;
        int rc = 0;

        gpa = scb_o->scaol & ~0xfUL;
        if (gpa) {
                if (!(gpa & ~0x1fffUL))
                        rc = set_validity_icpt(scb_s, 0x0038U);
                else if ((gpa & ~0x1fffUL) == kvm_s390_get_prefix(vcpu))
                        rc = set_validity_icpt(scb_s, 0x0011U);
                else if ((gpa & PAGE_MASK) !=
                         ((gpa + sizeof(struct bsca_block) - 1) & PAGE_MASK))
                        rc = set_validity_icpt(scb_s, 0x003bU);
                if (!rc) {
                        rc = pin_guest_page(vcpu->kvm, gpa, &hpa);
                        if (rc == -EINVAL)
                                rc = set_validity_icpt(scb_s, 0x0034U);
                }
                if (rc)
                        goto unpin;
                scb_s->scaoh = (u32)((u64)hpa >> 32);
                scb_s->scaol = (u32)(u64)hpa;
        }
        return 0;
unpin:
        unpin_blocks(vcpu, vsie_page);
        return rc;
}

/* unpin the scb provided by guest 2, marking it as dirty */
static void unpin_scb(struct kvm_vcpu *vcpu, struct vsie_page *vsie_page,
                      gpa_t gpa)
{
        hpa_t hpa = (hpa_t) vsie_page->scb_o;

        if (hpa)
                unpin_guest_page(vcpu->kvm, gpa, hpa);
        vsie_page->scb_o = NULL;
}

/*
 * Pin the scb at gpa provided by guest 2 at vsie_page->scb_o.
 *
 * Returns: - 0 if the scb was pinned.
 *          - > 0 if control has to be given to guest 2
 *          - -ENOMEM if out of memory
 */
static int pin_scb(struct kvm_vcpu *vcpu, struct vsie_page *vsie_page,
                   gpa_t gpa)
{
        hpa_t hpa;
        int rc;

        rc = pin_guest_page(vcpu->kvm, gpa, &hpa);
        if (rc == -EINVAL) {
                rc = kvm_s390_inject_program_int(vcpu, PGM_ADDRESSING);
                if (!rc)
                        rc = 1;
        }
        if (!rc)
                vsie_page->scb_o = (struct kvm_s390_sie_block *) hpa;
        return rc;
}

/*
 * Inject a fault into guest 2.
 *
 * Returns: - > 0 if control has to be given to guest 2
 *            < 0 if an error occurred during injection.
 */
static int inject_fault(struct kvm_vcpu *vcpu, __u16 code, __u64 vaddr,
                        bool write_flag)
{
        struct kvm_s390_pgm_info pgm = {
                .code = code,
                .trans_exc_code =
                        /* 0-51: virtual address */
                        (vaddr & 0xfffffffffffff000UL) |
                        /* 52-53: store / fetch */
                        (((unsigned int) !write_flag) + 1) << 10,
                        /* 62-63: asce id (alway primary == 0) */
                .exc_access_id = 0, /* always primary */
                .op_access_id = 0, /* not MVPG */
        };
        int rc;

        if (code == PGM_PROTECTION)
                pgm.trans_exc_code |= 0x4UL;

        rc = kvm_s390_inject_prog_irq(vcpu, &pgm);
        return rc ? rc : 1;
}

/*
 * Handle a fault during vsie execution on a gmap shadow.
 *
 * Returns: - 0 if the fault was resolved
 *          - > 0 if control has to be given to guest 2
 *          - < 0 if an error occurred
 */
static int handle_fault(struct kvm_vcpu *vcpu, struct vsie_page *vsie_page)
{
        int rc;

        if (current->thread.gmap_int_code == PGM_PROTECTION)
                /* we can directly forward all protection exceptions */
                return inject_fault(vcpu, PGM_PROTECTION,
                                    current->thread.gmap_addr, 1);

        rc = kvm_s390_shadow_fault(vcpu, vsie_page->gmap,
                                   current->thread.gmap_addr);
        if (rc > 0) {
                rc = inject_fault(vcpu, rc,
                                  current->thread.gmap_addr,
                                  current->thread.gmap_write_flag);
        }
        return rc;
}

static inline void clear_vsie_icpt(struct vsie_page *vsie_page)
{
        vsie_page->scb_s.icptcode = 0;
}

/*
 * Run the vsie on a shadow scb and a shadow gmap, without any further
 * sanity checks, handling SIE faults.
 *
 * Returns: - 0 everything went fine
 *          - > 0 if control has to be given to guest 2
 *          - < 0 if an error occurred
 */
static int do_vsie_run(struct kvm_vcpu *vcpu, struct vsie_page *vsie_page)
{
        struct kvm_s390_sie_block *scb_s = &vsie_page->scb_s;
        struct kvm_s390_sie_block *scb_o = vsie_page->scb_o;
        int rc;

        if (need_resched())
                schedule();
        if (test_cpu_flag(CIF_MCCK_PENDING))
                s390_handle_mcck();

        srcu_read_unlock(&vcpu->kvm->srcu, vcpu->srcu_idx);
        local_irq_disable();
        kvm_guest_enter();
        local_irq_enable();

        rc = sie64a(scb_s, vcpu->run->s.regs.gprs);

        local_irq_disable();
        kvm_guest_exit();
        local_irq_enable();
        vcpu->srcu_idx = srcu_read_lock(&vcpu->kvm->srcu);

        if (rc > 0)
                rc = 0; /* we could still have an icpt */
        else if (rc == -EFAULT)
                return handle_fault(vcpu, vsie_page);

        switch (scb_s->icptcode) {
        case ICPT_STOP:
                /* stop not requested by g2 - must have been a kick */
                if (!(atomic_read(&scb_o->cpuflags) & CPUSTAT_STOP_INT))
                        clear_vsie_icpt(vsie_page);
                break;
        case ICPT_VALIDITY:
                if ((scb_s->ipa & 0xf000) != 0xf000)
                        scb_s->ipa += 0x1000;
                break;
        }
        return rc;
}

static void release_gmap_shadow(struct vsie_page *vsie_page)
{
        if (vsie_page->gmap)
                gmap_put(vsie_page->gmap);
        WRITE_ONCE(vsie_page->gmap, NULL);
        prefix_unmapped(vsie_page);
}

static int acquire_gmap_shadow(struct kvm_vcpu *vcpu,
                               struct vsie_page *vsie_page)
{
        unsigned long asce;
        union ctlreg0 cr0;
        struct gmap *gmap;
        int edat;

        asce = vcpu->arch.sie_block->gcr[1];
        cr0.val = vcpu->arch.sie_block->gcr[0];
        edat = cr0.edat && test_kvm_facility(vcpu->kvm, 8);
        edat += edat && test_kvm_facility(vcpu->kvm, 78);

        /*
         * ASCE or EDAT could have changed since last icpt, or the gmap
         * we're holding has been unshadowed. If the gmap is still valid,
         * we can safely reuse it.
         */
        if (vsie_page->gmap && gmap_shadow_valid(vsie_page->gmap, asce, edat))
                return 0;

        /* release the old shadow - if any, and mark the prefix as unmapped */
        release_gmap_shadow(vsie_page);
        gmap = gmap_shadow(vcpu->arch.gmap, asce, edat);
        if (IS_ERR(gmap))
                return PTR_ERR(gmap);
        gmap->private = vcpu->kvm;
        WRITE_ONCE(vsie_page->gmap, gmap);
        return 0;
}

/*
 * Run the vsie on a shadowed scb, managing the gmap shadow, handling
 * prefix pages and faults.
 *
 * Returns: - 0 if no errors occurred
 *          - > 0 if control has to be given to guest 2
 *          - -ENOMEM if out of memory
 */
static int vsie_run(struct kvm_vcpu *vcpu, struct vsie_page *vsie_page)
{
        struct kvm_s390_sie_block *scb_s = &vsie_page->scb_s;
        int rc = 0;

        while (1) {
                rc = acquire_gmap_shadow(vcpu, vsie_page);
                if (!rc)
                        rc = map_prefix(vcpu, vsie_page);
                if (!rc) {
                        gmap_enable(vsie_page->gmap);
                        update_intervention_requests(vsie_page);
                        rc = do_vsie_run(vcpu, vsie_page);
                        gmap_enable(vcpu->arch.gmap);
                }

                if (rc == -EAGAIN)
                        rc = 0;
                if (rc || scb_s->icptcode || signal_pending(current) ||
                    kvm_s390_vcpu_has_irq(vcpu, 0))
                        break;
        };

        if (rc == -EFAULT) {
                /*
                 * Addressing exceptions are always presentes as intercepts.
                 * As addressing exceptions are suppressing and our guest 3 PSW
                 * points at the responsible instruction, we have to
                 * forward the PSW and set the ilc. If we can't read guest 3
                 * instruction, we can use an arbitrary ilc. Let's always use
                 * ilen = 4 for now, so we can avoid reading in guest 3 virtual
                 * memory. (we could also fake the shadow so the hardware
                 * handles it).
                 */
                scb_s->icptcode = ICPT_PROGI;
                scb_s->iprcc = PGM_ADDRESSING;
                scb_s->pgmilc = 4;
                scb_s->gpsw.addr = __rewind_psw(scb_s->gpsw, 4);
        }
        return rc;
}

/*
 * Get or create a vsie page for a scb address.
 *
 * Returns: - address of a vsie page (cached or new one)
 *          - NULL if the same scb address is already used by another VCPU
 *          - ERR_PTR(-ENOMEM) if out of memory
 */
static struct vsie_page *get_vsie_page(struct kvm *kvm, unsigned long addr)
{
        struct vsie_page *vsie_page;
        struct page *page;
        int nr_vcpus;

        rcu_read_lock();
        page = radix_tree_lookup(&kvm->arch.vsie.addr_to_page, addr >> 9);
        rcu_read_unlock();
        if (page) {
                if (page_ref_inc_return(page) == 2)
                        return page_to_virt(page);
                page_ref_dec(page);
        }

        /*
         * We want at least #online_vcpus shadows, so every VCPU can execute
         * the VSIE in parallel.
         */
        nr_vcpus = atomic_read(&kvm->online_vcpus);

        mutex_lock(&kvm->arch.vsie.mutex);
        if (kvm->arch.vsie.page_count < nr_vcpus) {
                page = alloc_page(GFP_KERNEL | __GFP_ZERO);
                if (!page) {
                        mutex_unlock(&kvm->arch.vsie.mutex);
                        return ERR_PTR(-ENOMEM);
                }
                page_ref_inc(page);
                kvm->arch.vsie.pages[kvm->arch.vsie.page_count] = page;
                kvm->arch.vsie.page_count++;
        } else {
                /* reuse an existing entry that belongs to nobody */
                while (true) {
                        page = kvm->arch.vsie.pages[kvm->arch.vsie.next];
                        if (page_ref_inc_return(page) == 2)
                                break;
                        page_ref_dec(page);
                        kvm->arch.vsie.next++;
                        kvm->arch.vsie.next %= nr_vcpus;
                }
                radix_tree_delete(&kvm->arch.vsie.addr_to_page, page->index >> 9);
        }
        page->index = addr;
        /* double use of the same address */
        if (radix_tree_insert(&kvm->arch.vsie.addr_to_page, addr >> 9, page)) {
                page_ref_dec(page);
                mutex_unlock(&kvm->arch.vsie.mutex);
                return NULL;
        }
        mutex_unlock(&kvm->arch.vsie.mutex);

        vsie_page = page_to_virt(page);
        memset(&vsie_page->scb_s, 0, sizeof(struct kvm_s390_sie_block));
        release_gmap_shadow(vsie_page);
        vsie_page->scb_s.ihcpu = 0xffffU;
        return vsie_page;
}

/* put a vsie page acquired via get_vsie_page */
static void put_vsie_page(struct kvm *kvm, struct vsie_page *vsie_page)
{
        struct page *page = pfn_to_page(__pa(vsie_page) >> PAGE_SHIFT);

        page_ref_dec(page);
}

int kvm_s390_handle_vsie(struct kvm_vcpu *vcpu)
{
        struct vsie_page *vsie_page;
        unsigned long scb_addr;
        int rc;

        vcpu->stat.instruction_sie++;
        if (!test_kvm_cpu_feat(vcpu->kvm, KVM_S390_VM_CPU_FEAT_SIEF2))
                return -EOPNOTSUPP;
        if (vcpu->arch.sie_block->gpsw.mask & PSW_MASK_PSTATE)
                return kvm_s390_inject_program_int(vcpu, PGM_PRIVILEGED_OP);

        BUILD_BUG_ON(sizeof(struct vsie_page) != 4096);
        scb_addr = kvm_s390_get_base_disp_s(vcpu, NULL);

        /* 512 byte alignment */
        if (unlikely(scb_addr & 0x1ffUL))
                return kvm_s390_inject_program_int(vcpu, PGM_SPECIFICATION);

        if (signal_pending(current) || kvm_s390_vcpu_has_irq(vcpu, 0))
                return 0;

        vsie_page = get_vsie_page(vcpu->kvm, scb_addr);
        if (IS_ERR(vsie_page))
                return PTR_ERR(vsie_page);
        else if (!vsie_page)
                /* double use of sie control block - simply do nothing */
                return 0;

        rc = pin_scb(vcpu, vsie_page, scb_addr);
        if (rc)
                goto out_put;
        rc = shadow_scb(vcpu, vsie_page);
        if (rc)
                goto out_unpin_scb;
        rc = pin_blocks(vcpu, vsie_page);
        if (rc)
                goto out_unshadow;
        rc = vsie_run(vcpu, vsie_page);
        unpin_blocks(vcpu, vsie_page);
out_unshadow:
        unshadow_scb(vcpu, vsie_page);
out_unpin_scb:
        unpin_scb(vcpu, vsie_page, scb_addr);
out_put:
        put_vsie_page(vcpu->kvm, vsie_page);

        return rc < 0 ? rc : 0;
}

/* Init the vsie data structures. To be called when a vm is initialized. */
void kvm_s390_vsie_init(struct kvm *kvm)
{
        mutex_init(&kvm->arch.vsie.mutex);
        INIT_RADIX_TREE(&kvm->arch.vsie.addr_to_page, GFP_KERNEL);
}

/* Destroy the vsie data structures. To be called when a vm is destroyed. */
void kvm_s390_vsie_destroy(struct kvm *kvm)
{
        struct vsie_page *vsie_page;
        struct page *page;
        int i;

        mutex_lock(&kvm->arch.vsie.mutex);
        for (i = 0; i < kvm->arch.vsie.page_count; i++) {
                page = kvm->arch.vsie.pages[i];
                kvm->arch.vsie.pages[i] = NULL;
                vsie_page = page_to_virt(page);
                release_gmap_shadow(vsie_page);
                /* free the radix tree entry */
                radix_tree_delete(&kvm->arch.vsie.addr_to_page, page->index >> 9);
                __free_page(page);
        }
        kvm->arch.vsie.page_count = 0;
        mutex_unlock(&kvm->arch.vsie.mutex);
}