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([2001:b07:6468:f312:5e2c:eb9a:a8b6:fd3e]) by smtp.gmail.com with ESMTPSA id d1sm15235952ede.31.2021.04.20.07.07.52 (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Tue, 20 Apr 2021 07:07:52 -0700 (PDT) Subject: Re: [PATCH v3 1/2] KVM: selftests: Sync data verify of dirty logging with guest sync To: Peter Xu Cc: linux-kernel@vger.kernel.org, kvm@vger.kernel.org, Andrew Jones , Sean Christopherson References: <20210417143602.215059-1-peterx@redhat.com> <20210417143602.215059-2-peterx@redhat.com> <20210418124351.GW4440@xz-x1> <60b0c96c-161d-676d-c30a-a7ffeccab417@redhat.com> <20210420131041.GZ4440@xz-x1> From: Paolo Bonzini Message-ID: Date: Tue, 20 Apr 2021 16:07:51 +0200 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:78.0) Gecko/20100101 Thunderbird/78.7.0 MIME-Version: 1.0 In-Reply-To: <20210420131041.GZ4440@xz-x1> Content-Type: text/plain; charset=utf-8; format=flowed Content-Language: en-US Content-Transfer-Encoding: 7bit Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On 20/04/21 15:10, Peter Xu wrote: > On Tue, Apr 20, 2021 at 10:07:16AM +0200, Paolo Bonzini wrote: >> On 18/04/21 14:43, Peter Xu wrote: >>> ----8<----- >>> diff --git a/tools/testing/selftests/kvm/dirty_log_test.c b/tools/testing/selftests/kvm/dirty_log_test.c >>> index 25230e799bc4..d3050d1c2cd0 100644 >>> --- a/tools/testing/selftests/kvm/dirty_log_test.c >>> +++ b/tools/testing/selftests/kvm/dirty_log_test.c >>> @@ -377,7 +377,7 @@ static void dirty_ring_after_vcpu_run(struct kvm_vm *vm, int ret, int err) >>> /* A ucall-sync or ring-full event is allowed */ >>> if (get_ucall(vm, VCPU_ID, NULL) == UCALL_SYNC) { >>> /* We should allow this to continue */ >>> - ; >>> + vcpu_handle_sync_stop(); >>> } else if (run->exit_reason == KVM_EXIT_DIRTY_RING_FULL || >>> (ret == -1 && err == EINTR)) { >>> /* Update the flag first before pause */ >>> ----8<----- >>> >>> That's my intention when I introduce vcpu_handle_sync_stop(), but forgot to >>> add... >> >> And possibly even this (untested though): >> >> diff --git a/tools/testing/selftests/kvm/dirty_log_test.c b/tools/testing/selftests/kvm/dirty_log_test.c >> index ffa4e2791926..918954f01cef 100644 >> --- a/tools/testing/selftests/kvm/dirty_log_test.c >> +++ b/tools/testing/selftests/kvm/dirty_log_test.c >> @@ -383,6 +383,7 @@ static void dirty_ring_after_vcpu_run(struct kvm_vm *vm, int ret, int err) >> /* Update the flag first before pause */ >> WRITE_ONCE(dirty_ring_vcpu_ring_full, >> run->exit_reason == KVM_EXIT_DIRTY_RING_FULL); >> + atomic_set(&vcpu_sync_stop_requested, false); >> sem_post(&sem_vcpu_stop); >> pr_info("vcpu stops because %s...\n", >> dirty_ring_vcpu_ring_full ? >> @@ -804,8 +805,7 @@ static void run_test(enum vm_guest_mode mode, void *arg) >> * the flush of the last page, and since we handle the last >> * page specially verification will succeed anyway. >> */ >> - assert(host_log_mode == LOG_MODE_DIRTY_RING || >> - atomic_read(&vcpu_sync_stop_requested) == false); >> + assert(atomic_read(&vcpu_sync_stop_requested) == false); >> vm_dirty_log_verify(mode, bmap); >> sem_post(&sem_vcpu_cont); >> >> You can submit all these as a separate patch. > > But it could race, then? > > main thread vcpu thread > ----------- ----------- > ring full > vcpu_sync_stop_requested=0 > sem_post(&sem_vcpu_stop) > vcpu_sync_stop_requested=1 > sem_wait(&sem_vcpu_stop) > assert(vcpu_sync_stop_requested==0) <---- Yes, it could indeed. Thanks, Paolo