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[35.185.214.157]) by smtp.gmail.com with ESMTPSA id d8-20020aa78e48000000b0050dc7628199sm5232277pfr.115.2022.05.02.16.55.27 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Mon, 02 May 2022 16:55:27 -0700 (PDT) Date: Mon, 2 May 2022 23:55:24 +0000 From: Sean Christopherson To: Paolo Bonzini , Vitaly Kuznetsov , Wanpeng Li , Jim Mattson , Joerg Roedel , kvm@vger.kernel.org, linux-kernel@vger.kernel.org, David Matlack , Ben Gardon Subject: Re: [PATCH v2] KVM: x86/mmu: Update number of zapped pages even if page list is stable Message-ID: References: <20211129235233.1277558-1-seanjc@google.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Fri, Apr 08, 2022, Sean Christopherson wrote: > Very high latency ping, this is still problematic and still applies cleanly. PING! PING! PING! PING! Don't make me write a script to ping you every hour :-) > On Mon, Nov 29, 2021, 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 > > Cc: stable@vger.kernel.org > > Signed-off-by: Sean Christopherson > > --- > > > > v2: > > - Rebase to kvm/master, commit 30d7c5d60a88 ("KVM: SEV: expose...") > > - Collect Ben's review, modulo bad splat. > > - Copy+paste the correct splat and symptom. [David]. > > > > @David, I kept the unstable declaration out of the loop, mostly because I > > really don't like putting declarations in loops, but also because > > nr_zapped is declared out of the loop and I didn't want to change that > > unnecessarily or make the code inconsistent. > > > > 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 0c839ee1282c..208c892136bf 100644 > > --- a/arch/x86/kvm/mmu/mmu.c > > +++ b/arch/x86/kvm/mmu/mmu.c > > @@ -5576,6 +5576,7 @@ 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, > > @@ -5607,11 +5608,12 @@ 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; > > - } > > } > > > > /* > > -- > > 2.34.0.rc2.393.gf8c9666880-goog >