2022-06-24 03:40:14

by Hou Wenlong

Subject: [PATCH 2/5] KVM: x86/mmu: Fix wrong gfn range of tlb flushing in kvm_set_pte_rmapp()

When the spte of hupe page is dropped in kvm_set_pte_rmapp(),
the whole gfn range covered by the spte should be flushed.
However, rmap_walk_init_level() doesn't align down the gfn
for new level like tdp iterator does, then the gfn used in
kvm_set_pte_rmapp() is not the base gfn of huge page. And
the size of gfn range is wrong too for huge page. Since
the base gfn of huge page is more meaningful during the
rmap walking, so align down the gfn for new level and use
the correct size of huge page for tlb flushing in
kvm_set_pte_rmapp().

Fixes: c3134ce240eed ("KVM: Replace old tlb flush function with new one to flush a specified range.")
Signed-off-by: Hou Wenlong <[email protected]>
---
arch/x86/kvm/mmu/mmu.c | 4 ++--
1 file changed, 2 insertions(+), 2 deletions(-)

diff --git a/arch/x86/kvm/mmu/mmu.c b/arch/x86/kvm/mmu/mmu.c
index b8a1f5b46b9d..37bfc88ea212 100644
--- a/arch/x86/kvm/mmu/mmu.c
+++ b/arch/x86/kvm/mmu/mmu.c
@@ -1427,7 +1427,7 @@ static bool kvm_set_pte_rmapp(struct kvm *kvm, struct kvm_rmap_head *rmap_head,
}

if (need_flush && kvm_available_flush_tlb_with_range()) {
- kvm_flush_remote_tlbs_with_address(kvm, gfn, 1);
+ kvm_flush_remote_tlbs_with_address(kvm, gfn, KVM_PAGES_PER_HPAGE(level));
return false;
}

@@ -1455,7 +1455,7 @@ static void
rmap_walk_init_level(struct slot_rmap_walk_iterator *iterator, int level)
{
iterator->level = level;
- iterator->gfn = iterator->start_gfn;
+ iterator->gfn = iterator->start_gfn & -KVM_PAGES_PER_HPAGE(level);
iterator->rmap = gfn_to_rmap(iterator->gfn, level, iterator->slot);
iterator->end_rmap = gfn_to_rmap(iterator->end_gfn, level, iterator->slot);
}
--
2.31.1

2022-06-24 23:13:51

by Sean Christopherson

Subject: Re: [PATCH 2/5] KVM: x86/mmu: Fix wrong gfn range of tlb flushing in kvm_set_pte_rmapp()

On Fri, Jun 24, 2022, Hou Wenlong wrote:
> When the spte of hupe page is dropped in kvm_set_pte_rmapp(),
> the whole gfn range covered by the spte should be flushed.
> However, rmap_walk_init_level() doesn't align down the gfn
> for new level like tdp iterator does, then the gfn used in
> kvm_set_pte_rmapp() is not the base gfn of huge page. And
> the size of gfn range is wrong too for huge page. Since
> the base gfn of huge page is more meaningful during the
> rmap walking, so align down the gfn for new level and use
> the correct size of huge page for tlb flushing in
> kvm_set_pte_rmapp().

It's also worth noting that kvm_set_pte_rmapp() is the other user of the rmap
iterators that consumes @gfn, i.e. modifying iterator->gfn is safe-ish.

> Fixes: c3134ce240eed ("KVM: Replace old tlb flush function with new one to flush a specified range.")
> Signed-off-by: Hou Wenlong <[email protected]>
> ---
> arch/x86/kvm/mmu/mmu.c | 4 ++--
> 1 file changed, 2 insertions(+), 2 deletions(-)
>
> diff --git a/arch/x86/kvm/mmu/mmu.c b/arch/x86/kvm/mmu/mmu.c
> index b8a1f5b46b9d..37bfc88ea212 100644
> --- a/arch/x86/kvm/mmu/mmu.c
> +++ b/arch/x86/kvm/mmu/mmu.c
> @@ -1427,7 +1427,7 @@ static bool kvm_set_pte_rmapp(struct kvm *kvm, struct kvm_rmap_head *rmap_head,
> }
>
> if (need_flush && kvm_available_flush_tlb_with_range()) {
> - kvm_flush_remote_tlbs_with_address(kvm, gfn, 1);
> + kvm_flush_remote_tlbs_with_address(kvm, gfn, KVM_PAGES_PER_HPAGE(level));
> return false;
> }
>
> @@ -1455,7 +1455,7 @@ static void
> rmap_walk_init_level(struct slot_rmap_walk_iterator *iterator, int level)
> {
> iterator->level = level;
> - iterator->gfn = iterator->start_gfn;
> + iterator->gfn = iterator->start_gfn & -KVM_PAGES_PER_HPAGE(level);

Hrm, arguably this be done on start_gfn in slot_rmap_walk_init(). Having iter->gfn
be less than iter->start_gfn will be odd.

> iterator->rmap = gfn_to_rmap(iterator->gfn, level, iterator->slot);
> iterator->end_rmap = gfn_to_rmap(iterator->end_gfn, level, iterator->slot);
> }
> --
> 2.31.1
>