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([2001:b07:6468:f312:5e2c:eb9a:a8b6:fd3e]) by smtp.gmail.com with ESMTPSA id p13sm1671750wrt.73.2020.11.06.03.27.54 (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Fri, 06 Nov 2020 03:27:55 -0800 (PST) To: Peter Xu , kvm@vger.kernel.org, linux-kernel@vger.kernel.org Cc: Sean Christopherson , "Dr . David Alan Gilbert" , Andrew Jones References: <20201001012044.5151-1-peterx@redhat.com> <20201001012239.6159-1-peterx@redhat.com> From: Paolo Bonzini Subject: Re: [PATCH v13 13/14] KVM: selftests: Let dirty_log_test async for dirty ring test Message-ID: <6d5eb99e-e068-e5a6-522f-07ef9c33127f@redhat.com> Date: Fri, 6 Nov 2020 12:27:54 +0100 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:78.0) Gecko/20100101 Thunderbird/78.3.1 MIME-Version: 1.0 In-Reply-To: <20201001012239.6159-1-peterx@redhat.com> Content-Type: text/plain; charset=utf-8; format=flowed Content-Language: en-US Content-Transfer-Encoding: 8bit Precedence: bulk List-ID: X-Mailing-List: kvm@vger.kernel.org On 01/10/20 03:22, Peter Xu wrote: > + > +static void vcpu_sig_handler(int sig) > +{ > + TEST_ASSERT(sig == SIG_IPI, "unknown signal: %d", sig); > +} > + Unless you also use run->immediate_exit in vcpu_kick, this is racy. The alternative is to _not_ set up a signal handler and instead block the signal. KVM_SET_SIGNAL_MASK unblocks the signal inside the VM and on -EINTR sigwait accepts the signal (removes it from the set of pending signal). This is a bit more complicated, but I think it's a good idea to do it this way for documentation purposes. Here is the patch: diff --git a/tools/testing/selftests/kvm/dirty_log_test.c b/tools/testing/selftests/kvm/dirty_log_test.c index 4b404dfdc2f9..9a5b876b74af 100644 --- a/tools/testing/selftests/kvm/dirty_log_test.c +++ b/tools/testing/selftests/kvm/dirty_log_test.c @@ -172,11 +172,6 @@ static pthread_t vcpu_thread; /* Only way to pass this to the signal handler */ static struct kvm_vm *current_vm; -static void vcpu_sig_handler(int sig) -{ - TEST_ASSERT(sig == SIG_IPI, "unknown signal: %d", sig); -} - static void vcpu_kick(void) { pthread_kill(vcpu_thread, SIG_IPI); @@ -484,13 +479,26 @@ static void *vcpu_worker(void *data) struct kvm_vm *vm = data; uint64_t *guest_array; uint64_t pages_count = 0; - struct sigaction sigact; + struct kvm_signal_mask *sigmask = alloca(offsetof(struct kvm_signal_mask, sigset) + + sizeof(sigset_t)); + sigset_t *sigset = (sigset_t *) &sigmask->sigset; current_vm = vm; vcpu_fd = vcpu_get_fd(vm, VCPU_ID); - memset(&sigact, 0, sizeof(sigact)); - sigact.sa_handler = vcpu_sig_handler; - sigaction(SIG_IPI, &sigact, NULL); + + /* + * SIG_IPI is unblocked atomically while in KVM_RUN. It causes the + * ioctl to return with -EINTR, but it is still pending and we need + * to accept it with the sigwait. + */ + sigmask->len = 8; + pthread_sigmask(0, NULL, sigset); + vcpu_ioctl(vm, VCPU_ID, KVM_SET_SIGNAL_MASK, sigmask); + sigaddset(sigset, SIG_IPI); + pthread_sigmask(SIG_BLOCK, sigset, NULL); + + sigemptyset(sigset); + sigaddset(sigset, SIG_IPI); guest_array = addr_gva2hva(vm, (vm_vaddr_t)random_array); @@ -500,6 +508,11 @@ static void *vcpu_worker(void *data) pages_count += TEST_PAGES_PER_LOOP; /* Let the guest dirty the random pages */ ret = ioctl(vcpu_fd, KVM_RUN, NULL); + if (ret == -EINTR) { + int sig = -1; + sigwait(sigset, &sig); + assert(sig == SIG_IPI); + } log_mode_after_vcpu_run(vm, ret, errno); }