| Message ID | 20210113205030.3481307-1-seanjc@google.com (mailing list archive) |
|---|---|
| State | New, archived |
| Headers | show |
| Series | KVM: x86: Zap the oldest MMU pages, not the newest | expand |
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
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.
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(-)