From d2cbae37c3d8f9ce1f33ae690421be6ecf3809d1 Mon Sep 17 00:00:00 2001 From: Sean Christopherson Date: Wed, 13 Jan 2021 12:50:30 -0800 Subject: [PATCH] KVM: x86: Zap the oldest MMU pages, not the newest commit 8fc517267fb28576dfca2380cc2497a2454b8fae upstream. 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 Cc: stable@vger.kernel.org Signed-off-by: Sean Christopherson Message-Id: <20210113205030.3481307-1-seanjc@google.com> Signed-off-by: Paolo Bonzini Signed-off-by: Greg Kroah-Hartman --- 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 52f36c8..dacbd13 100644 --- a/arch/x86/kvm/mmu/mmu.c +++ b/arch/x86/kvm/mmu/mmu.c @@ -2409,7 +2409,7 @@ 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. -- 2.7.4