Re: [PATCH v8 6/8] KVM: Update lpage info when private/shared memory are mixed

[Isaku Yamahata]

On Thu, Sep 15, 2022 at 10:29:11PM +0800,
Chao Peng <chao.p.peng@linux.intel.com> wrote:

> diff --git a/arch/x86/kvm/mmu/mmu.c b/arch/x86/kvm/mmu/mmu.c
> index 08abad4f3e6f..a0f198cede3d 100644
> --- a/arch/x86/kvm/mmu/mmu.c
> +++ b/arch/x86/kvm/mmu/mmu.c
...
> @@ -6894,3 +6899,115 @@ void kvm_mmu_pre_destroy_vm(struct kvm *kvm)
>       if (kvm->arch.nx_lpage_recovery_thread)
>               kthread_stop(kvm->arch.nx_lpage_recovery_thread);
>  }
> +
> +static bool mem_attr_is_mixed(struct kvm *kvm, unsigned int attr,
> +                           gfn_t start, gfn_t end)
> +{
> +     XA_STATE(xas, &kvm->mem_attr_array, start);
> +     gfn_t gfn = start;
> +     void *entry;
> +     bool shared, private;
> +     bool mixed = false;
> +
> +     if (attr == KVM_MEM_ATTR_SHARED) {
> +             shared = true;
> +             private = false;
> +     } else {
> +             shared = false;
> +             private = true;
> +     }

We don't have to care the target is shared or private.  We need to check
only same or not.

> +
> +     rcu_read_lock();
> +     entry = xas_load(&xas);
> +     while (gfn < end) {
> +             if (xas_retry(&xas, entry))
> +                     continue;
> +
> +             KVM_BUG_ON(gfn != xas.xa_index, kvm);
> +
> +             if (entry)
> +                     private = true;
> +             else
> +                     shared = true;
> +
> +             if (private && shared) {
> +                     mixed = true;
> +                     goto out;
> +             }
> +
> +             entry = xas_next(&xas);
> +             gfn++;
> +     }
> +out:
> +     rcu_read_unlock();
> +     return mixed;
> +}
> +
> +static inline void update_mixed(struct kvm_lpage_info *linfo, bool mixed)
> +{
> +     if (mixed)
> +             linfo->disallow_lpage |= KVM_LPAGE_PRIVATE_SHARED_MIXED;
> +     else
> +             linfo->disallow_lpage &= ~KVM_LPAGE_PRIVATE_SHARED_MIXED;
> +}
> +
> +static void update_mem_lpage_info(struct kvm *kvm,
> +                               struct kvm_memory_slot *slot,
> +                               unsigned int attr,
> +                               gfn_t start, gfn_t end)
> +{
> +     unsigned long lpage_start, lpage_end;
> +     unsigned long gfn, pages, mask;
> +     int level;
> +
> +     for (level = PG_LEVEL_2M; level <= KVM_MAX_HUGEPAGE_LEVEL; level++) {
> +             pages = KVM_PAGES_PER_HPAGE(level);
> +             mask = ~(pages - 1);
> +             lpage_start = start & mask;
> +             lpage_end = (end - 1) & mask;
> +
> +             /*
> +              * We only need to scan the head and tail page, for middle pages
> +              * we know they are not mixed.
> +              */
> +             update_mixed(lpage_info_slot(lpage_start, slot, level),
> +                          mem_attr_is_mixed(kvm, attr, lpage_start,
> +                                                       lpage_start + pages));
> +
> +             if (lpage_start == lpage_end)
> +                     return;
> +
> +             for (gfn = lpage_start + pages; gfn < lpage_end; gfn += pages)
> +                     update_mixed(lpage_info_slot(gfn, slot, level), false);


For >2M case, we don't have to check all entry. just check lower level case.

> +
> +             update_mixed(lpage_info_slot(lpage_end, slot, level),
> +                          mem_attr_is_mixed(kvm, attr, lpage_end,
> +                                                       lpage_end + pages));
> +     }
> +}
> +
> +void kvm_arch_update_mem_attr(struct kvm *kvm, unsigned int attr,
> +                           gfn_t start, gfn_t end)
> +{
> +     struct kvm_memory_slot *slot;
> +     struct kvm_memslots *slots;
> +     struct kvm_memslot_iter iter;
> +     int i;
> +
> +     WARN_ONCE(!(attr & (KVM_MEM_ATTR_PRIVATE | KVM_MEM_ATTR_SHARED)),
> +                     "Unsupported mem attribute.\n");
> +
> +     for (i = 0; i < KVM_ADDRESS_SPACE_NUM; i++) {
> +             slots = __kvm_memslots(kvm, i);
> +
> +             kvm_for_each_memslot_in_gfn_range(&iter, slots, start, end) {
> +                     slot = iter.slot;
> +                     start = max(start, slot->base_gfn);
> +                     end = min(end, slot->base_gfn + slot->npages);
> +                     if (WARN_ON_ONCE(start >= end))
> +                             continue;
> +
> +                     update_mem_lpage_info(kvm, slot, attr, start, end);
> +             }
> +     }
> +}


Here is my updated version.

bool kvm_mem_attr_is_mixed(struct kvm_memory_slot *slot, gfn_t gfn, int level)
{
        gfn_t pages = KVM_PAGES_PER_HPAGE(level);
        gfn_t mask = ~(pages - 1);
        struct kvm_lpage_info *linfo = lpage_info_slot(gfn & mask, slot, level);

        WARN_ON_ONCE(level == PG_LEVEL_4K);
        return linfo->disallow_lpage & KVM_LPAGE_PRIVATE_SHARED_MIXED;
}

#ifdef CONFIG_HAVE_KVM_PRIVATE_MEM_ATTR
static void update_mixed(struct kvm_lpage_info *linfo, bool mixed)
{
        if (mixed)
                linfo->disallow_lpage |= KVM_LPAGE_PRIVATE_SHARED_MIXED;
        else
                linfo->disallow_lpage &= ~KVM_LPAGE_PRIVATE_SHARED_MIXED;
}

static bool __mem_attr_is_mixed(struct kvm *kvm, gfn_t start, gfn_t end)
{
        XA_STATE(xas, &kvm->mem_attr_array, start);
        bool mixed = false;
        gfn_t gfn = start;
        void *s_entry;
        void *entry;

        rcu_read_lock();
        s_entry = xas_load(&xas);
        entry = s_entry;
        while (gfn < end) {
                if (xas_retry(&xas, entry))
                        continue;

                KVM_BUG_ON(gfn != xas.xa_index, kvm);

                entry = xas_next(&xas);
                if (entry != s_entry) {
                        mixed = true;
                        break;
                }
                gfn++;
        }
        rcu_read_unlock();
        return mixed;
}

static bool mem_attr_is_mixed(struct kvm *kvm,
                              struct kvm_memory_slot *slot, int level,
                              gfn_t start, gfn_t end)
{
        struct kvm_lpage_info *child_linfo;
        unsigned long child_pages;
        bool mixed = false;
        unsigned long gfn;
        void *entry;

        if (WARN_ON_ONCE(level == PG_LEVEL_4K))
                return false;

        if (level == PG_LEVEL_2M)
                return __mem_attr_is_mixed(kvm, start, end);

        /* This assumes that level - 1 is already updated. */
        rcu_read_lock();
        child_pages = KVM_PAGES_PER_HPAGE(level - 1);
        entry = xa_load(&kvm->mem_attr_array, start);
        for (gfn = start; gfn < end; gfn += child_pages) {
                child_linfo = lpage_info_slot(gfn, slot, level - 1);
                if (child_linfo->disallow_lpage & 
KVM_LPAGE_PRIVATE_SHARED_MIXED) {
                        mixed = true;
                        break;
                }
                if (xa_load(&kvm->mem_attr_array, gfn) != entry) {
                        mixed = true;
                        break;
                }
        }
        rcu_read_unlock();
        return mixed;
}

static void update_mem_lpage_info(struct kvm *kvm,
                                  struct kvm_memory_slot *slot,
                                  unsigned int attr,
                                  gfn_t start, gfn_t end)
{
        unsigned long lpage_start, lpage_end;
        unsigned long gfn, pages, mask;
        int level;

        for (level = PG_LEVEL_2M; level <= KVM_MAX_HUGEPAGE_LEVEL; level++) {
                pages = KVM_PAGES_PER_HPAGE(level);
                mask = ~(pages - 1);
                lpage_start = start & mask;
                lpage_end = (end - 1) & mask;

                /*
                 * We only need to scan the head and tail page, for middle pages
                 * we know they are not mixed.
                 */
                update_mixed(lpage_info_slot(lpage_start, slot, level),
                             mem_attr_is_mixed(kvm, slot, level,
                                               lpage_start, lpage_start + 
pages));

                if (lpage_start == lpage_end)
                        return;

                for (gfn = lpage_start + pages; gfn < lpage_end; gfn += pages)
                        update_mixed(lpage_info_slot(gfn, slot, level), false);

                update_mixed(lpage_info_slot(lpage_end, slot, level),
                             mem_attr_is_mixed(kvm, slot, level,
                                               lpage_end, lpage_end + pages));
        }
}

void kvm_arch_update_mem_attr(struct kvm *kvm, unsigned int attr,
                              gfn_t start, gfn_t end)
{
        struct kvm_memory_slot *slot;
        struct kvm_memslots *slots;
        struct kvm_memslot_iter iter;
        int idx;
        int i;

        WARN_ONCE(!(attr & (KVM_MEM_ATTR_PRIVATE | KVM_MEM_ATTR_SHARED)),
                  "Unsupported mem attribute.\n");

        idx = srcu_read_lock(&kvm->srcu);
        for (i = 0; i < KVM_ADDRESS_SPACE_NUM; i++) {
                slots = __kvm_memslots(kvm, i);

                kvm_for_each_memslot_in_gfn_range(&iter, slots, start, end) {
                        slot = iter.slot;
                        start = max(start, slot->base_gfn);
                        end = min(end, slot->base_gfn + slot->npages);
                        if (WARN_ON_ONCE(start >= end))
                                continue;

                        update_mem_lpage_info(kvm, slot, attr, start, end);
                }
        }
        srcu_read_unlock(&kvm->srcu, idx);
}
#endif


-- 
Isaku Yamahata <isaku.yamahata@gmail.com>