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([2001:b07:6468:f312:c8dd:75d4:99ab:290a]) by smtp.gmail.com with ESMTPSA id i9sm19267323wrn.54.2021.06.09.00.51.52 (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Wed, 09 Jun 2021 00:51:53 -0700 (PDT) Subject: Re: [PATCH] KVM: Fix dirty ring mmap incorrect size due to renaming accident To: Peter Xu , qemu-devel@nongnu.org References: <20210609014355.217110-1-peterx@redhat.com> From: Paolo Bonzini Message-ID: <17006e0c-72ff-3c8a-dd72-b4054020eb38@redhat.com> Date: Wed, 9 Jun 2021 09:51:52 +0200 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:78.0) Gecko/20100101 Thunderbird/78.10.1 MIME-Version: 1.0 In-Reply-To: <20210609014355.217110-1-peterx@redhat.com> Authentication-Results: relay.mimecast.com; auth=pass smtp.auth=CUSA124A263 smtp.mailfrom=pbonzini@redhat.com X-Mimecast-Spam-Score: 0 X-Mimecast-Originator: redhat.com Content-Type: text/plain; charset=utf-8; format=flowed Content-Language: en-US Content-Transfer-Encoding: 7bit Received-SPF: pass client-ip=216.205.24.124; envelope-from=pbonzini@redhat.com; helo=us-smtp-delivery-124.mimecast.com X-Spam_score_int: -29 X-Spam_score: -3.0 X-Spam_bar: --- X-Spam_report: (-3.0 / 5.0 requ) BAYES_00=-1.9, DKIMWL_WL_HIGH=-0.197, DKIM_SIGNED=0.1, DKIM_VALID=-0.1, DKIM_VALID_AU=-0.1, DKIM_VALID_EF=-0.1, NICE_REPLY_A=-0.001, RCVD_IN_DNSWL_LOW=-0.7, RCVD_IN_MSPIKE_H4=0.001, RCVD_IN_MSPIKE_WL=0.001, SPF_HELO_NONE=0.001, SPF_PASS=-0.001 autolearn=ham autolearn_force=no X-Spam_action: no action X-BeenThere: qemu-devel@nongnu.org X-Mailman-Version: 2.1.23 Precedence: list List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Cc: Hyman Huang , "Dr . David Alan Gilbert" Errors-To: qemu-devel-bounces+qemu-devel=archiver.kernel.org@nongnu.org Sender: "Qemu-devel" On 09/06/21 03:43, Peter Xu wrote: > Found this when I wanted to try the per-vcpu dirty rate series out, then I > found that it's not really working and it can quickly hang death a guest. I > found strange errors (e.g. guest crash after migration) happens even without > the per-vcpu dirty rate series. > > When merging dirty ring, probably no one notice that the trivial renaming diff > [1] missed two existing references of kvm_dirty_ring_sizes; they do matter > since otherwise we'll mmap() a shorter range of memory after the renaming. > > I think it didn't SIGBUS for me easily simply because some other stuff within > qemu mmap()ed right after the dirty rings (e.g. when testing 4096 slots, it > aligned with one small page on x86), so when we access the rings we've been > reading/writting to random memory elsewhere of qemu. > > Fix the two sizes when map/unmap the shared dirty gfn memory. > > [1] https://lore.kernel.org/qemu-devel/dac5f0c6-1bca-3daf-e5d2-6451dbbaca93@redhat.com/ > > Cc: Hyman Huang > Cc: Paolo Bonzini > Cc: Dr. David Alan Gilbert > Signed-off-by: Peter Xu > --- > accel/kvm/kvm-all.c | 4 ++-- > 1 file changed, 2 insertions(+), 2 deletions(-) > > diff --git a/accel/kvm/kvm-all.c b/accel/kvm/kvm-all.c > index c7ec5388500..e5b10dd129c 100644 > --- a/accel/kvm/kvm-all.c > +++ b/accel/kvm/kvm-all.c > @@ -411,7 +411,7 @@ static int do_kvm_destroy_vcpu(CPUState *cpu) > } > > if (cpu->kvm_dirty_gfns) { > - ret = munmap(cpu->kvm_dirty_gfns, s->kvm_dirty_ring_size); > + ret = munmap(cpu->kvm_dirty_gfns, s->kvm_dirty_ring_bytes); > if (ret < 0) { > goto err; > } > @@ -495,7 +495,7 @@ int kvm_init_vcpu(CPUState *cpu, Error **errp) > > if (s->kvm_dirty_ring_size) { > /* Use MAP_SHARED to share pages with the kernel */ > - cpu->kvm_dirty_gfns = mmap(NULL, s->kvm_dirty_ring_size, > + cpu->kvm_dirty_gfns = mmap(NULL, s->kvm_dirty_ring_bytes, > PROT_READ | PROT_WRITE, MAP_SHARED, > cpu->kvm_fd, > PAGE_SIZE * KVM_DIRTY_LOG_PAGE_OFFSET); > Oops, sorry. I queued it. Paolo