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Wed, 1 Jul 2020 21:36:46 +0300 Date: Wed, 1 Jul 2020 21:36:45 +0300 From: Roman Bolshakov To: Paolo Bonzini Subject: Re: [PATCH v2 4/9] i386: hvf: Implement CPU kick Message-ID: <20200701183645.GC78555@SPB-NB-133.local> References: <20200630102824.77604-1-r.bolshakov@yadro.com> <20200630102824.77604-5-r.bolshakov@yadro.com> <20200630155059.GA78555@SPB-NB-133.local> <2ba7aa12-9eba-1cef-93e0-5561f50629b9@redhat.com> MIME-Version: 1.0 Content-Type: text/plain; charset="us-ascii" Content-Disposition: inline In-Reply-To: <2ba7aa12-9eba-1cef-93e0-5561f50629b9@redhat.com> X-Originating-IP: [172.17.204.212] X-ClientProxiedBy: T-EXCH-01.corp.yadro.com (172.17.10.101) To T-EXCH-02.corp.yadro.com (172.17.10.102) Received-SPF: pass client-ip=89.207.88.252; envelope-from=r.bolshakov@yadro.com; helo=mta-01.yadro.com X-detected-operating-system: by eggs.gnu.org: First seen = 2020/07/01 14:36:48 X-ACL-Warn: Detected OS = Linux 3.11 and newer X-Spam_score_int: -20 X-Spam_score: -2.1 X-Spam_bar: -- X-Spam_report: (-2.1 / 5.0 requ) BAYES_00=-1.9, DKIM_SIGNED=0.1, DKIM_VALID=-0.1, DKIM_VALID_AU=-0.1, DKIM_VALID_EF=-0.1, SPF_HELO_NONE=0.001, SPF_PASS=-0.001, URIBL_BLOCKED=0.001 autolearn=_AUTOLEARN 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: Eduardo Habkost , qemu-devel@nongnu.org, Cameron Esfahani , Claudio Fontana , Richard Henderson Errors-To: qemu-devel-bounces+qemu-devel=archiver.kernel.org@nongnu.org Sender: "Qemu-devel" On Tue, Jun 30, 2020 at 06:04:23PM +0200, Paolo Bonzini wrote: > On 30/06/20 17:50, Roman Bolshakov wrote: > > On Tue, Jun 30, 2020 at 02:33:42PM +0200, Paolo Bonzini wrote: > >> Can a signal interrupt hv_vcpu_run? If so you actually don't need > >> hv_vcpu_interrupt at all. > > > > Existing signal masking and SIG_IPI didn't work IIRC when I tried to add > > a primitive version of gdbstub support. > > You can try pthread_kill followed by hv_vcpu_interrupt if it doesn't. > The signal would be delivered after return to userspace. > I looked at the signal setup for HVF again. I was wrong with regards to SIG_IPI. It isn't delivered to vCPU because the signal is masked, this fixes it: diff --git a/target/i386/hvf/hvf.c b/target/i386/hvf/hvf.c index d81f569aed..7bf05bca21 100644 --- a/target/i386/hvf/hvf.c +++ b/target/i386/hvf/hvf.c @@ -479,6 +479,7 @@ int hvf_init_vcpu(CPUState *cpu) pthread_sigmask(SIG_BLOCK, NULL, &set); sigdelset(&set, SIG_IPI); + pthread_sigmask(SIG_SETMASK, &set, NULL); init_emu(); init_decoder(); But the signal is delivered only after vmxexit, perhaps a sequence of pthread_kill() and hv_vcpu_interrupt() is really needed. So, there are two race windows on kernel-to-user border in v2: just before checking the deadline and vmenter and just after vmxexit and re-arm of preemption timer, that's two places where kicks could be lost. The approach you proposed seems to address them. Thanks, Roman > >> You can also require the preemption time, all > >> processor that support HVF have it, but never set it by default. The > >> deadline can be left at 0 all the time; instead, you toggle the bit in > >> the pin-based controls. In the signal handler you do: > >> > >> if (atomic_xchg(&env->hvf_in_guest, false)) { > >> wvmcs(cpu->hvf_fd, VMCS_PIN_BASED_CTLS, > >> rvmcs(cpu->hvf_fd, VMCS_PIN_BASED_CTLS) > >> | VMCS_PIN_BASED_CTLS_VMX_PREEMPT_TIMER); > >> } > >> > >> In the main loop you do: > >> > >> atomic_set(&env->hvf_guest_mode, true); > >> smp_mb(); > >> hv_vcpu_run(...); > >> atomic_set(&env->hvf_guest_mode, false); > >> > >> and in the preemption timer vmexit handler: > >> > >> wvmcs(cpu->hvf_fd, VMCS_PIN_BASED_CTLS, > >> rvmcs(cpu->hvf_fd, VMCS_PIN_BASED_CTLS) > >> & ~VMCS_PIN_BASED_CTLS_VMX_PREEMPT_TIMER); > >> > >