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    SubjectRe: [PATCH v10 7/9] KVM: Update lpage info when private/shared memory are mixed
    On Fri, Dec 02, 2022 at 02:13:45PM +0800,
    Chao Peng <chao.p.peng@linux.intel.com> wrote:

    > A large page with mixed private/shared subpages can't be mapped as large
    > page since its sub private/shared pages are from different memory
    > backends and may also treated by architecture differently. When
    > private/shared memory are mixed in a large page, the current lpage_info
    > is not sufficient to decide whether the page can be mapped as large page
    > or not and additional private/shared mixed information is needed.
    >
    > Tracking this 'mixed' information with the current 'count' like
    > disallow_lpage is a bit challenge so reserve a bit in 'disallow_lpage'
    > to indicate a large page has mixed private/share subpages and update
    > this 'mixed' bit whenever the memory attribute is changed between
    > private and shared.
    >
    > Signed-off-by: Chao Peng <chao.p.peng@linux.intel.com>
    > ---
    > arch/x86/include/asm/kvm_host.h | 8 ++
    > arch/x86/kvm/mmu/mmu.c | 134 +++++++++++++++++++++++++++++++-
    > arch/x86/kvm/x86.c | 2 +
    > include/linux/kvm_host.h | 19 +++++
    > virt/kvm/kvm_main.c | 9 ++-
    > 5 files changed, 169 insertions(+), 3 deletions(-)
    >
    > diff --git a/arch/x86/include/asm/kvm_host.h b/arch/x86/include/asm/kvm_host.h
    > index 283cbb83d6ae..7772ab37ac89 100644
    > --- a/arch/x86/include/asm/kvm_host.h
    > +++ b/arch/x86/include/asm/kvm_host.h
    > @@ -38,6 +38,7 @@
    > #include <asm/hyperv-tlfs.h>
    >
    > #define __KVM_HAVE_ARCH_VCPU_DEBUGFS
    > +#define __KVM_HAVE_ARCH_SET_MEMORY_ATTRIBUTES
    >
    > #define KVM_MAX_VCPUS 1024
    >
    > @@ -1011,6 +1012,13 @@ struct kvm_vcpu_arch {
    > #endif
    > };
    >
    > +/*
    > + * Use a bit in disallow_lpage to indicate private/shared pages mixed at the
    > + * level. The remaining bits are used as a reference count.
    > + */
    > +#define KVM_LPAGE_PRIVATE_SHARED_MIXED (1U << 31)
    > +#define KVM_LPAGE_COUNT_MAX ((1U << 31) - 1)
    > +
    > struct kvm_lpage_info {
    > int disallow_lpage;
    > };
    > diff --git a/arch/x86/kvm/mmu/mmu.c b/arch/x86/kvm/mmu/mmu.c
    > index e2c70b5afa3e..2190fd8c95c0 100644
    > --- a/arch/x86/kvm/mmu/mmu.c
    > +++ b/arch/x86/kvm/mmu/mmu.c
    > @@ -763,11 +763,16 @@ static void update_gfn_disallow_lpage_count(const struct kvm_memory_slot *slot,
    > {
    > struct kvm_lpage_info *linfo;
    > int i;
    > + int disallow_count;
    >
    > for (i = PG_LEVEL_2M; i <= KVM_MAX_HUGEPAGE_LEVEL; ++i) {
    > linfo = lpage_info_slot(gfn, slot, i);
    > +
    > + disallow_count = linfo->disallow_lpage & KVM_LPAGE_COUNT_MAX;
    > + WARN_ON(disallow_count + count < 0 ||
    > + disallow_count > KVM_LPAGE_COUNT_MAX - count);
    > +
    > linfo->disallow_lpage += count;
    > - WARN_ON(linfo->disallow_lpage < 0);
    > }
    > }
    >
    > @@ -6986,3 +6991,130 @@ void kvm_mmu_pre_destroy_vm(struct kvm *kvm)
    > if (kvm->arch.nx_huge_page_recovery_thread)
    > kthread_stop(kvm->arch.nx_huge_page_recovery_thread);
    > }
    > +
    > +static bool linfo_is_mixed(struct kvm_lpage_info *linfo)
    > +{
    > + return linfo->disallow_lpage & KVM_LPAGE_PRIVATE_SHARED_MIXED;
    > +}
    > +
    > +static void linfo_set_mixed(gfn_t gfn, struct kvm_memory_slot *slot,
    > + int level, bool mixed)
    > +{
    > + struct kvm_lpage_info *linfo = lpage_info_slot(gfn, slot, level);
    > +
    > + if (mixed)
    > + linfo->disallow_lpage |= KVM_LPAGE_PRIVATE_SHARED_MIXED;
    > + else
    > + linfo->disallow_lpage &= ~KVM_LPAGE_PRIVATE_SHARED_MIXED;
    > +}
    > +
    > +static bool is_expected_attr_entry(void *entry, unsigned long expected_attrs)
    > +{
    > + bool expect_private = expected_attrs & KVM_MEMORY_ATTRIBUTE_PRIVATE;
    > +
    > + if (xa_to_value(entry) & KVM_MEMORY_ATTRIBUTE_PRIVATE) {
    > + if (!expect_private)
    > + return false;
    > + } else if (expect_private)
    > + return false;
    > +
    > + return true;
    > +}
    > +
    > +static bool mem_attrs_mixed_2m(struct kvm *kvm, unsigned long attrs,
    > + gfn_t start, gfn_t end)
    > +{
    > + XA_STATE(xas, &kvm->mem_attr_array, start);
    > + gfn_t gfn = start;
    > + void *entry;
    > + bool mixed = false;
    > +
    > + 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 (!is_expected_attr_entry(entry, attrs)) {
    > + mixed = true;
    > + break;
    > + }
    > +
    > + entry = xas_next(&xas);
    > + gfn++;
    > + }
    > +
    > + rcu_read_unlock();
    > + return mixed;
    > +}
    > +
    > +static bool mem_attrs_mixed(struct kvm *kvm, struct kvm_memory_slot *slot,
    > + int level, unsigned long attrs,
    > + gfn_t start, gfn_t end)
    > +{
    > + unsigned long gfn;
    > +
    > + if (level == PG_LEVEL_2M)
    > + return mem_attrs_mixed_2m(kvm, attrs, start, end);
    > +
    > + for (gfn = start; gfn < end; gfn += KVM_PAGES_PER_HPAGE(level - 1))
    > + if (linfo_is_mixed(lpage_info_slot(gfn, slot, level - 1)) ||
    > + !is_expected_attr_entry(xa_load(&kvm->mem_attr_array, gfn),
    > + attrs))
    > + return true;
    > + return false;
    > +}
    > +
    > +static void kvm_update_lpage_private_shared_mixed(struct kvm *kvm,
    > + struct kvm_memory_slot *slot,
    > + unsigned long attrs,
    > + gfn_t start, gfn_t end)
    > +{
    > + unsigned long pages, mask;
    > + gfn_t gfn, gfn_end, first, last;
    > + int level;
    > + bool mixed;
    > +
    > + /*
    > + * The sequence matters here: we set the higher level basing on the
    > + * lower level's scanning result.
    > + */
    > + for (level = PG_LEVEL_2M; level <= KVM_MAX_HUGEPAGE_LEVEL; level++) {
    > + pages = KVM_PAGES_PER_HPAGE(level);
    > + mask = ~(pages - 1);
    > + first = start & mask;
    > + last = (end - 1) & mask;
    > +
    > + /*
    > + * We only need to scan the head and tail page, for middle pages
    > + * we know they will not be mixed.
    > + */
    > + gfn = max(first, slot->base_gfn);
    > + gfn_end = min(first + pages, slot->base_gfn + slot->npages);
    > + mixed = mem_attrs_mixed(kvm, slot, level, attrs, gfn, gfn_end);
    > + linfo_set_mixed(gfn, slot, level, mixed);
    > +
    > + if (first == last)
    > + return;


    continue.

    > +
    > + for (gfn = first + pages; gfn < last; gfn += pages)
    > + linfo_set_mixed(gfn, slot, level, false);
    > +
    > + gfn = last;
    > + gfn_end = min(last + pages, slot->base_gfn + slot->npages);

    if (gfn == gfn_end) continue.


    > + mixed = mem_attrs_mixed(kvm, slot, level, attrs, gfn, gfn_end);
    > + linfo_set_mixed(gfn, slot, level, mixed);
    > + }
    > +}
    > +
    > +void kvm_arch_set_memory_attributes(struct kvm *kvm,
    > + struct kvm_memory_slot *slot,
    > + unsigned long attrs,
    > + gfn_t start, gfn_t end)
    > +{
    > + if (kvm_slot_can_be_private(slot))
    > + kvm_update_lpage_private_shared_mixed(kvm, slot, attrs,
    > + start, end);
    > +}
    > diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c
    > index 9a07380f8d3c..5aefcff614d2 100644
    > --- a/arch/x86/kvm/x86.c
    > +++ b/arch/x86/kvm/x86.c
    > @@ -12362,6 +12362,8 @@ static int kvm_alloc_memslot_metadata(struct kvm *kvm,
    > if ((slot->base_gfn + npages) & (KVM_PAGES_PER_HPAGE(level) - 1))
    > linfo[lpages - 1].disallow_lpage = 1;
    > ugfn = slot->userspace_addr >> PAGE_SHIFT;
    > + if (kvm_slot_can_be_private(slot))
    > + ugfn |= slot->restricted_offset >> PAGE_SHIFT;

    Is there any alignment restriction? If no, It should be +=.
    In practice, alignment will hold though.

    Thanks,

    > /*
    > * If the gfn and userspace address are not aligned wrt each
    > * other, disable large page support for this slot.
    > diff --git a/include/linux/kvm_host.h b/include/linux/kvm_host.h
    > index 3331c0c92838..25099c94e770 100644
    > --- a/include/linux/kvm_host.h
    > +++ b/include/linux/kvm_host.h
    > @@ -592,6 +592,11 @@ struct kvm_memory_slot {
    > struct restrictedmem_notifier notifier;
    > };
    >
    > +static inline bool kvm_slot_can_be_private(const struct kvm_memory_slot *slot)
    > +{
    > + return slot && (slot->flags & KVM_MEM_PRIVATE);
    > +}
    > +
    > static inline bool kvm_slot_dirty_track_enabled(const struct kvm_memory_slot *slot)
    > {
    > return slot->flags & KVM_MEM_LOG_DIRTY_PAGES;
    > @@ -2316,4 +2321,18 @@ static inline void kvm_account_pgtable_pages(void *virt, int nr)
    > /* Max number of entries allowed for each kvm dirty ring */
    > #define KVM_DIRTY_RING_MAX_ENTRIES 65536
    >
    > +#ifdef __KVM_HAVE_ARCH_SET_MEMORY_ATTRIBUTES
    > +void kvm_arch_set_memory_attributes(struct kvm *kvm,
    > + struct kvm_memory_slot *slot,
    > + unsigned long attrs,
    > + gfn_t start, gfn_t end);
    > +#else
    > +static inline void kvm_arch_set_memory_attributes(struct kvm *kvm,
    > + struct kvm_memory_slot *slot,
    > + unsigned long attrs,
    > + gfn_t start, gfn_t end)
    > +{
    > +}
    > +#endif /* __KVM_HAVE_ARCH_SET_MEMORY_ATTRIBUTES */
    > +
    > #endif
    > diff --git a/virt/kvm/kvm_main.c b/virt/kvm/kvm_main.c
    > index 4e1e1e113bf0..e107afea32f0 100644
    > --- a/virt/kvm/kvm_main.c
    > +++ b/virt/kvm/kvm_main.c
    > @@ -2354,7 +2354,8 @@ static u64 kvm_supported_mem_attributes(struct kvm *kvm)
    > return 0;
    > }
    >
    > -static void kvm_unmap_mem_range(struct kvm *kvm, gfn_t start, gfn_t end)
    > +static void kvm_unmap_mem_range(struct kvm *kvm, gfn_t start, gfn_t end,
    > + unsigned long attrs)
    > {
    > struct kvm_gfn_range gfn_range;
    > struct kvm_memory_slot *slot;
    > @@ -2378,6 +2379,10 @@ static void kvm_unmap_mem_range(struct kvm *kvm, gfn_t start, gfn_t end)
    > gfn_range.slot = slot;
    >
    > r |= kvm_unmap_gfn_range(kvm, &gfn_range);
    > +
    > + kvm_arch_set_memory_attributes(kvm, slot, attrs,
    > + gfn_range.start,
    > + gfn_range.end);
    > }
    > }
    >
    > @@ -2427,7 +2432,7 @@ static int kvm_vm_ioctl_set_mem_attributes(struct kvm *kvm,
    > idx = srcu_read_lock(&kvm->srcu);
    > KVM_MMU_LOCK(kvm);
    > if (i > start)
    > - kvm_unmap_mem_range(kvm, start, i);
    > + kvm_unmap_mem_range(kvm, start, i, attrs->attributes);
    > kvm_mmu_invalidate_end(kvm);
    > KVM_MMU_UNLOCK(kvm);
    > srcu_read_unlock(&kvm->srcu, idx);
    > --
    > 2.25.1
    >

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

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