[PATCH 1/2] kvm: mmu: fix catch transparent huge page backing

[PATCH 1/2] kvm: mmu: fix catch transparent huge page backing

[Wanpeng Li]

PageTransCompound() can't guarantee the page is a transparent huge page
since it returns true for both transparent huge and hugetlbfs pages.

This patch fixes it by checking the page is also !hugetlbfs page.

Signed-off-by: Wanpeng Li <wanpeng.li@linux.intel.com>
---
 arch/x86/kvm/mmu.c | 3 ++-
 1 file changed, 2 insertions(+), 1 deletion(-)

diff --git a/arch/x86/kvm/mmu.c b/arch/x86/kvm/mmu.c
index 146f295..2a0d77e 100644
--- a/arch/x86/kvm/mmu.c
+++ b/arch/x86/kvm/mmu.c
@@ -4487,7 +4487,8 @@ static bool kvm_mmu_zap_collapsible_spte(struct kvm *kvm,
 		 */
 		if (sp->role.direct &&
 			!kvm_is_reserved_pfn(pfn) &&
-			PageTransCompound(pfn_to_page(pfn))) {
+			!PageHuge(pfn_to_page(pfn)) &&
+			PageTransHuge(pfn_to_page(pfn))) {
 			drop_spte(kvm, sptep);
 			sptep = rmap_get_first(*rmapp, &iter);
 			need_tlb_flush = 1;
-- 
1.9.1

[PATCH 2/2] kvm: mmu: don't do overflow memslot check

[Wanpeng Li]

As Andre pointed out:

| I don't understand the value of this check here. Are we looking for a
| broken memslot? Shouldn't this be a BUG_ON? Is this the place to care
| about these things? npages is capped to KVM_MEM_MAX_NR_PAGES, i.e.
| 2^31. A 64 bit overflow would be caused by a gigantic gfn_start which
| would be trouble in many other ways.

This patch drops the memslot overflow check to make the codes more simple.

Signed-off-by: Wanpeng Li <wanpeng.li@linux.intel.com>
---
 arch/x86/kvm/mmu.c | 12 ++----------
 1 file changed, 2 insertions(+), 10 deletions(-)

diff --git a/arch/x86/kvm/mmu.c b/arch/x86/kvm/mmu.c
index 2a0d77e..9265fda 100644
--- a/arch/x86/kvm/mmu.c
+++ b/arch/x86/kvm/mmu.c
@@ -4505,19 +4505,12 @@ void kvm_mmu_zap_collapsible_sptes(struct kvm *kvm,
 	bool flush = false;
 	unsigned long *rmapp;
 	unsigned long last_index, index;
-	gfn_t gfn_start, gfn_end;
 
 	spin_lock(&kvm->mmu_lock);
 
-	gfn_start = memslot->base_gfn;
-	gfn_end = memslot->base_gfn + memslot->npages - 1;
-
-	if (gfn_start >= gfn_end)
-		goto out;
-
 	rmapp = memslot->arch.rmap[0];
-	last_index = gfn_to_index(gfn_end, memslot->base_gfn,
-					PT_PAGE_TABLE_LEVEL);
+	last_index = gfn_to_index(memslot->base_gfn + memslot->npages - 1,
+				memslot->base_gfn, PT_PAGE_TABLE_LEVEL);
 
 	for (index = 0; index <= last_index; ++index, ++rmapp) {
 		if (*rmapp)
@@ -4535,7 +4528,6 @@ void kvm_mmu_zap_collapsible_sptes(struct kvm *kvm,
 	if (flush)
 		kvm_flush_remote_tlbs(kvm);
 
-out:
 	spin_unlock(&kvm->mmu_lock);
 }
 
-- 
1.9.1

Re: [PATCH 2/2] kvm: mmu: don't do overflow memslot check

[Andres Lagar-Cavilla]

On Mon, Apr 13, 2015 at 10:51 PM, Wanpeng Li <wanpeng.li@linux.intel.com> wrote:
> As Andre pointed out:
(Andres)
>
> | I don't understand the value of this check here. Are we looking for a
> | broken memslot? Shouldn't this be a BUG_ON? Is this the place to care
> | about these things? npages is capped to KVM_MEM_MAX_NR_PAGES, i.e.
> | 2^31. A 64 bit overflow would be caused by a gigantic gfn_start which
> | would be trouble in many other ways.
>
> This patch drops the memslot overflow check to make the codes more simple.
>
> Signed-off-by: Wanpeng Li <wanpeng.li@linux.intel.com>
Reviewed-by: Andres Lagar-Cavilla <andreslc@google.com>

Thanks
> ---
>  arch/x86/kvm/mmu.c | 12 ++----------
>  1 file changed, 2 insertions(+), 10 deletions(-)
>
> diff --git a/arch/x86/kvm/mmu.c b/arch/x86/kvm/mmu.c
> index 2a0d77e..9265fda 100644
> --- a/arch/x86/kvm/mmu.c
> +++ b/arch/x86/kvm/mmu.c
> @@ -4505,19 +4505,12 @@ void kvm_mmu_zap_collapsible_sptes(struct kvm *kvm,
>         bool flush = false;
>         unsigned long *rmapp;
>         unsigned long last_index, index;
> -       gfn_t gfn_start, gfn_end;
>
>         spin_lock(&kvm->mmu_lock);
>
> -       gfn_start = memslot->base_gfn;
> -       gfn_end = memslot->base_gfn + memslot->npages - 1;
> -
> -       if (gfn_start >= gfn_end)
> -               goto out;
> -
>         rmapp = memslot->arch.rmap[0];
> -       last_index = gfn_to_index(gfn_end, memslot->base_gfn,
> -                                       PT_PAGE_TABLE_LEVEL);
> +       last_index = gfn_to_index(memslot->base_gfn + memslot->npages - 1,
> +                               memslot->base_gfn, PT_PAGE_TABLE_LEVEL);
>
>         for (index = 0; index <= last_index; ++index, ++rmapp) {
>                 if (*rmapp)
> @@ -4535,7 +4528,6 @@ void kvm_mmu_zap_collapsible_sptes(struct kvm *kvm,
>         if (flush)
>                 kvm_flush_remote_tlbs(kvm);
>
> -out:
>         spin_unlock(&kvm->mmu_lock);
>  }
>
> --
> 1.9.1
>



-- 
Andres Lagar-Cavilla | Google Kernel Team | andreslc@google.com