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SubjectRe: [PATCH] KVM: x86: Zap the oldest MMU pages, not the newest
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On 13/01/21 21:50, Sean Christopherson wrote:
> Walk the list of MMU pages in reverse in kvm_mmu_zap_oldest_mmu_pages().
> The list is FIFO, meaning new pages are inserted at the head and thus
> the oldest pages are at the tail. Using a "forward" iterator causes KVM
> to zap MMU pages that were just added, which obliterates guest
> performance once the max number of shadow MMU pages is reached.
>
> Fixes: 6b82ef2c9cf1 ("KVM: x86/mmu: Batch zap MMU pages when recycling oldest pages")
> Reported-by: Zdenek Kaspar <zkaspar82@gmail.com>
> Cc: stable@vger.kernel.org
> Signed-off-by: Sean Christopherson <seanjc@google.com>
> ---
> arch/x86/kvm/mmu/mmu.c | 2 +-
> 1 file changed, 1 insertion(+), 1 deletion(-)
>
> diff --git a/arch/x86/kvm/mmu/mmu.c b/arch/x86/kvm/mmu/mmu.c
> index 6d16481aa29d..ed861245ecf0 100644
> --- a/arch/x86/kvm/mmu/mmu.c
> +++ b/arch/x86/kvm/mmu/mmu.c
> @@ -2417,7 +2417,7 @@ static unsigned long kvm_mmu_zap_oldest_mmu_pages(struct kvm *kvm,
> return 0;
>
> restart:
> - list_for_each_entry_safe(sp, tmp, &kvm->arch.active_mmu_pages, link) {
> + list_for_each_entry_safe_reverse(sp, tmp, &kvm->arch.active_mmu_pages, link) {
> /*
> * Don't zap active root pages, the page itself can't be freed
> * and zapping it will just force vCPUs to realloc and reload.
>

Queued for 5.11, thanks.

Paolo

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