Re: [PATCH v9 6/8] KVM: Update lpage info when private/shared memory are mixed

Yuan Yao
2022-11-08T12:08:36Z

On Tue, Oct 25, 2022 at 11:13:42PM +0800, Chao Peng wrote:
> When private/shared memory are mixed in a large page, the lpage_info may
> not be accurate and should be updated with this mixed info. A large page
> has mixed pages can't be really mapped as large page since its
> private/shared pages are from different physical memory.
>
> Update lpage_info when private/shared memory attribute is changed. If
> both private and shared pages are within a large page region, it can't
> be mapped as large page. It's a bit challenge to track the mixed
> info in a 'count' like variable, this patch instead reserves a bit in
> 'disallow_lpage' to indicate a large page has mixed private/share pages.
>
> 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 | 112 +++++++++++++++++++++++++++++++-
> arch/x86/kvm/x86.c | 2 +
> include/linux/kvm_host.h | 19 ++++++
> virt/kvm/kvm_main.c | 16 +++--
> 5 files changed, 152 insertions(+), 5 deletions(-)
>
> diff --git a/arch/x86/include/asm/kvm_host.h b/arch/x86/include/asm/kvm_host.h
> index 7551b6f9c31c..db811a54e3fd 100644
> --- a/arch/x86/include/asm/kvm_host.h
> +++ b/arch/x86/include/asm/kvm_host.h
> @@ -37,6 +37,7 @@
> #include <asm/hyperv-tlfs.h>
>
> #define __KVM_HAVE_ARCH_VCPU_DEBUGFS
> +#define __KVM_HAVE_ARCH_UPDATE_MEM_ATTR
>
> #define KVM_MAX_VCPUS 1024
>
> @@ -952,6 +953,13 @@ 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 33b1aec44fb8..67a9823a8c35 100644
> --- a/arch/x86/kvm/mmu/mmu.c
> +++ b/arch/x86/kvm/mmu/mmu.c
> @@ -762,11 +762,16 @@ 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);
> }
> }
>
> @@ -6910,3 +6915,108 @@ 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 inline bool linfo_is_mixed(struct kvm_lpage_info *linfo)
> +{
> + return linfo->disallow_lpage & KVM_LPAGE_PRIVATE_SHARED_MIXED;
> +}
> +
> +static inline void linfo_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_2m(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 = attr == KVM_MEM_ATTR_SHARED;
> + 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 ((entry && !shared) || (!entry && shared)) {
> + mixed = true;
> + goto out;
> + }
> +
> + entry = xas_next(&xas);
> + gfn++;
> + }
> +out:
> + rcu_read_unlock();
> + return mixed;
> +}
> +
> +static bool mem_attr_is_mixed(struct kvm *kvm, struct kvm_memory_slot *slot,
> + int level, unsigned int attr,
> + gfn_t start, gfn_t end)
> +{
> + unsigned long gfn;
> + void *entry;
> +
> + if (level == PG_LEVEL_2M)
> + return mem_attr_is_mixed_2m(kvm, attr, start, end);
> +
> + entry = xa_load(&kvm->mem_attr_array, start);
> + for (gfn = start; gfn < end; gfn += KVM_PAGES_PER_HPAGE(level - 1)) {
> + if (linfo_is_mixed(lpage_info_slot(gfn, slot, level - 1)))
> + return true;
> + if (xa_load(&kvm->mem_attr_array, gfn) != entry)
> + return true;
> + }
> + return false;
> +}
> +
> +void kvm_arch_update_mem_attr(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;
> +
> + WARN_ONCE(!(attr & (KVM_MEM_ATTR_PRIVATE | KVM_MEM_ATTR_SHARED)),
> + "Unsupported mem attribute.\n");
> +
> + /*
> + * The sequence matters here: we update 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);
> + lpage_start = max(start & mask, slot->base_gfn);
> + lpage_end = (end - 1) & mask;
> +
> + /*
> + * We only need to scan the head and tail page, for middle pages
> + * we know they are not mixed.
> + */
> + linfo_update_mixed(lpage_info_slot(lpage_start, slot, level),
> + mem_attr_is_mixed(kvm, slot, level, attr,
> + lpage_start, start));

Looks only query the lpage_start, start is not enough:

A and B are private gfns from same lpage_start as below, A > B :
lpage_start
|---------A
|----B

Convert A to shared, this makes the upper 2M page to MIX.
Convert B to shared, this also makes the upper 2M page to MIX.
Convert B to private, this makes the upper 2M page to Non-MIX, but
it's incorrect, due to A is shared.

Same to tail case.

> +
> + if (lpage_start == lpage_end)
> + return;
> +
> + for (gfn = lpage_start + pages; gfn < lpage_end; gfn += pages)
> + linfo_update_mixed(lpage_info_slot(gfn, slot, level),
> + false);
> +
> + linfo_update_mixed(lpage_info_slot(lpage_end, slot, level),
> + mem_attr_is_mixed(kvm, slot, level, attr,
> + end, lpage_end + pages));
> + }
> +}
> diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c
> index 02ad31f46dd7..4276ca73bd7b 100644
> --- a/arch/x86/kvm/x86.c
> +++ b/arch/x86/kvm/x86.c
> @@ -12563,6 +12563,8 @@ 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;
> /*
> * 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 4ce98fa0153c..6ce36065532c 100644
> --- a/include/linux/kvm_host.h
> +++ b/include/linux/kvm_host.h
> @@ -2284,4 +2284,23 @@ 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 CONFIG_KVM_GENERIC_PRIVATE_MEM
> +
> +#define KVM_MEM_ATTR_SHARED 0x0001
> +#define KVM_MEM_ATTR_PRIVATE 0x0002
> +
> +#ifdef __KVM_HAVE_ARCH_UPDATE_MEM_ATTR
> +void kvm_arch_update_mem_attr(struct kvm *kvm, struct kvm_memory_slot *slot,
> + unsigned int attr, gfn_t start, gfn_t end);
> +#else
> +static inline void kvm_arch_update_mem_attr(struct kvm *kvm,
> + struct kvm_memory_slot *slot,
> + unsigned int attr,
> + gfn_t start, gfn_t end)
> +{
> +}
> +#endif
> +
> +#endif /* CONFIG_KVM_GENERIC_PRIVATE_MEM */
> +
> #endif
> diff --git a/virt/kvm/kvm_main.c b/virt/kvm/kvm_main.c
> index fc3835826ace..13a37b4d9e97 100644
> --- a/virt/kvm/kvm_main.c
> +++ b/virt/kvm/kvm_main.c
> @@ -939,7 +939,8 @@ static int kvm_init_mmu_notifier(struct kvm *kvm)
>
> #ifdef CONFIG_KVM_GENERIC_PRIVATE_MEM
>
> -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 int attr)
> {
> struct kvm_gfn_range gfn_range;
> struct kvm_memory_slot *slot;
> @@ -963,6 +964,7 @@ 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_update_mem_attr(kvm, slot, attr, start, end);
> }
> }
>
> @@ -970,7 +972,6 @@ static void kvm_unmap_mem_range(struct kvm *kvm, gfn_t start, gfn_t end)
> kvm_flush_remote_tlbs(kvm);
> }
>
> -#define KVM_MEM_ATTR_SHARED 0x0001
> static int kvm_vm_ioctl_set_mem_attr(struct kvm *kvm, gpa_t gpa, gpa_t size,
> bool is_private)
> {
> @@ -979,6 +980,7 @@ static int kvm_vm_ioctl_set_mem_attr(struct kvm *kvm, gpa_t gpa, gpa_t size,
> void *entry;
> int idx;
> int r = 0;
> + unsigned int attr;
>
> if (size == 0 || gpa + size < gpa)
> return -EINVAL;
> @@ -992,7 +994,13 @@ static int kvm_vm_ioctl_set_mem_attr(struct kvm *kvm, gpa_t gpa, gpa_t size,
> * Guest memory defaults to private, kvm->mem_attr_array only stores
> * shared memory.
> */
> - entry = is_private ? NULL : xa_mk_value(KVM_MEM_ATTR_SHARED);
> + if (is_private) {
> + attr = KVM_MEM_ATTR_PRIVATE;
> + entry = NULL;
> + } else {
> + attr = KVM_MEM_ATTR_SHARED;
> + entry = xa_mk_value(KVM_MEM_ATTR_SHARED);
> + }
>
> idx = srcu_read_lock(&kvm->srcu);
> KVM_MMU_LOCK(kvm);
> @@ -1005,7 +1013,7 @@ static int kvm_vm_ioctl_set_mem_attr(struct kvm *kvm, gpa_t gpa, gpa_t size,
> goto err;
> }
>
> - kvm_unmap_mem_range(kvm, start, end);
> + kvm_unmap_mem_range(kvm, start, end, attr);
>
> goto ret;
> err:
> --
> 2.25.1
>