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([2001:b07:6468:f312:c8dd:75d4:99ab:290a]) by smtp.googlemail.com with ESMTPSA id y18-20020aa7ccd2000000b0042617ba6394sm2565060edt.30.2022.05.12.07.11.41 (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Thu, 12 May 2022 07:11:44 -0700 (PDT) Sender: Paolo Bonzini Message-ID: Date: Thu, 12 May 2022 16:11:40 +0200 MIME-Version: 1.0 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:91.0) Gecko/20100101 Thunderbird/91.8.0 Subject: Re: [PATCH v3] KVM: x86/mmu: Update number of zapped pages even if page list is stable Content-Language: en-US To: Sean Christopherson Cc: Vitaly Kuznetsov , Wanpeng Li , Jim Mattson , Joerg Roedel , kvm@vger.kernel.org, linux-kernel@vger.kernel.org, David Matlack , Ben Gardon References: <20220511145122.3133334-1-seanjc@google.com> From: Paolo Bonzini In-Reply-To: <20220511145122.3133334-1-seanjc@google.com> Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 7bit Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On 5/11/22 16:51, Sean Christopherson wrote: > When zapping obsolete pages, update the running count of zapped pages > regardless of whether or not the list has become unstable due to zapping > a shadow page with its own child shadow pages. If the VM is backed by > mostly 4kb pages, KVM can zap an absurd number of SPTEs without bumping > the batch count and thus without yielding. In the worst case scenario, > this can cause a soft lokcup. > > watchdog: BUG: soft lockup - CPU#12 stuck for 22s! [dirty_log_perf_:13020] > RIP: 0010:workingset_activation+0x19/0x130 > mark_page_accessed+0x266/0x2e0 > kvm_set_pfn_accessed+0x31/0x40 > mmu_spte_clear_track_bits+0x136/0x1c0 > drop_spte+0x1a/0xc0 > mmu_page_zap_pte+0xef/0x120 > __kvm_mmu_prepare_zap_page+0x205/0x5e0 > kvm_mmu_zap_all_fast+0xd7/0x190 > kvm_mmu_invalidate_zap_pages_in_memslot+0xe/0x10 > kvm_page_track_flush_slot+0x5c/0x80 > kvm_arch_flush_shadow_memslot+0xe/0x10 > kvm_set_memslot+0x1a8/0x5d0 > __kvm_set_memory_region+0x337/0x590 > kvm_vm_ioctl+0xb08/0x1040 > > Fixes: fbb158cb88b6 ("KVM: x86/mmu: Revert "Revert "KVM: MMU: zap pages in batch""") > Reported-by: David Matlack > Reviewed-by: Ben Gardon > Reviewed-by: David Matlack > Cc: stable@vger.kernel.org > Signed-off-by: Sean Christopherson > --- > > v3: > - Collect David's review. > - "Rebase". The v2 patch still applies cleanly, but Paolo apparently has > a filter configured to ignore all emails related to the v2 submission. > > v2: > - https://lore.kernel.org/all/20211129235233.1277558-1-seanjc@google.com > - Rebase to kvm/master, commit 30d7c5d60a88 ("KVM: SEV: expose...") > - Collect Ben's review, modulo bad splat. > - Copy+paste the correct splat and symptom. [David]. > > arch/x86/kvm/mmu/mmu.c | 10 ++++++---- > 1 file changed, 6 insertions(+), 4 deletions(-) > > diff --git a/arch/x86/kvm/mmu/mmu.c b/arch/x86/kvm/mmu/mmu.c > index 909372762363..7429ae1784af 100644 > --- a/arch/x86/kvm/mmu/mmu.c > +++ b/arch/x86/kvm/mmu/mmu.c > @@ -5665,6 +5665,7 @@ static void kvm_zap_obsolete_pages(struct kvm *kvm) > { > struct kvm_mmu_page *sp, *node; > int nr_zapped, batch = 0; > + bool unstable; > > restart: > list_for_each_entry_safe_reverse(sp, node, > @@ -5696,11 +5697,12 @@ static void kvm_zap_obsolete_pages(struct kvm *kvm) > goto restart; > } > > - if (__kvm_mmu_prepare_zap_page(kvm, sp, > - &kvm->arch.zapped_obsolete_pages, &nr_zapped)) { > - batch += nr_zapped; > + unstable = __kvm_mmu_prepare_zap_page(kvm, sp, > + &kvm->arch.zapped_obsolete_pages, &nr_zapped); > + batch += nr_zapped; > + > + if (unstable) > goto restart; > - } > } > > /* > > base-commit: 2764011106d0436cb44702cfb0981339d68c3509 Queued, thanks. Paolo