From: Sean Christopherson Date: Wed, 13 Jan 2021 20:50:30 +0000 (-0800) Subject: KVM: x86: Zap the oldest MMU pages, not the newest X-Git-Tag: io_uring-worker.v3-2021-02-25~38^2~151 X-Git-Url: https://git.kernel.dk/?a=commitdiff_plain;h=8fc517267fb28576dfca2380cc2497a2454b8fae;p=linux-block.git KVM: x86: Zap the oldest MMU pages, not the newest 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 --- 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.