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[91.219.240.2]) by smtp.gmail.com with ESMTPSA id n13sm2429121ejk.97.2021.06.04.00.35.27 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Fri, 04 Jun 2021 00:35:28 -0700 (PDT) From: Vitaly Kuznetsov To: Eduardo Habkost Subject: Re: [PATCH v7 8/9] i386: Hyper-V SynIC requires POST_MESSAGES/SIGNAL_EVENTS priviliges In-Reply-To: <20210603230017.3goxm7fdu5fpdkdw@habkost.net> References: <20210603114835.847451-1-vkuznets@redhat.com> <20210603114835.847451-9-vkuznets@redhat.com> <20210603230017.3goxm7fdu5fpdkdw@habkost.net> Date: Fri, 04 Jun 2021 09:35:27 +0200 Message-ID: <871r9i13r4.fsf@vitty.brq.redhat.com> MIME-Version: 1.0 Authentication-Results: relay.mimecast.com; auth=pass smtp.auth=CUSA124A263 smtp.mailfrom=vkuznets@redhat.com X-Mimecast-Spam-Score: 0 X-Mimecast-Originator: redhat.com Content-Type: text/plain Received-SPF: pass client-ip=216.205.24.124; envelope-from=vkuznets@redhat.com; helo=us-smtp-delivery-124.mimecast.com X-Spam_score_int: -31 X-Spam_score: -3.2 X-Spam_bar: --- X-Spam_report: (-3.2 / 5.0 requ) BAYES_00=-1.9, DKIMWL_WL_HIGH=-0.37, DKIM_SIGNED=0.1, DKIM_VALID=-0.1, DKIM_VALID_AU=-0.1, DKIM_VALID_EF=-0.1, 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: Paolo Bonzini , Marcelo Tosatti , qemu-devel@nongnu.org, Igor Mammedov Errors-To: qemu-devel-bounces+qemu-devel=archiver.kernel.org@nongnu.org Sender: "Qemu-devel" Eduardo Habkost writes: > On Thu, Jun 03, 2021 at 01:48:34PM +0200, Vitaly Kuznetsov wrote: >> When Hyper-V SynIC is enabled, we may need to allow Windows guests to make >> hypercalls (POST_MESSAGES/SIGNAL_EVENTS). No issue is currently observed >> because KVM is very permissive, allowing these hypercalls regarding of >> guest visible CPUid bits. >> >> Signed-off-by: Vitaly Kuznetsov >> --- >> target/i386/kvm/hyperv-proto.h | 6 ++++++ >> target/i386/kvm/kvm.c | 6 ++++++ >> 2 files changed, 12 insertions(+) >> >> diff --git a/target/i386/kvm/hyperv-proto.h b/target/i386/kvm/hyperv-proto.h >> index e30d64b4ade4..5fbb385cc136 100644 >> --- a/target/i386/kvm/hyperv-proto.h >> +++ b/target/i386/kvm/hyperv-proto.h >> @@ -38,6 +38,12 @@ >> #define HV_ACCESS_FREQUENCY_MSRS (1u << 11) >> #define HV_ACCESS_REENLIGHTENMENTS_CONTROL (1u << 13) >> >> +/* >> + * HV_CPUID_FEATURES.EBX bits >> + */ >> +#define HV_POST_MESSAGES (1u << 4) >> +#define HV_SIGNAL_EVENTS (1u << 5) >> + >> /* >> * HV_CPUID_FEATURES.EDX bits >> */ >> diff --git a/target/i386/kvm/kvm.c b/target/i386/kvm/kvm.c >> index a3897d4d8788..6a32d43e6ec1 100644 >> --- a/target/i386/kvm/kvm.c >> +++ b/target/i386/kvm/kvm.c >> @@ -1343,6 +1343,12 @@ static int hyperv_fill_cpuids(CPUState *cs, >> /* Unconditionally required with any Hyper-V enlightenment */ >> c->eax |= HV_HYPERCALL_AVAILABLE; >> >> + /* SynIC and Vmbus devices require messages/signals hypercalls */ >> + if (hyperv_feat_enabled(cpu, HYPERV_FEAT_SYNIC) && >> + !cpu->hyperv_synic_kvm_only) { >> + c->ebx |= HV_POST_MESSAGES | HV_SIGNAL_EVENTS; > > Why exactly is the hyperv_synic_kvm_only check needed? > 'hyperv_synic_kvm_only' means SynIC is only used for in-KVM stimers and in this case Post Messages / Signal Events hypercalls are not used. KVM will also return an error to the guest directly (as it can't forward them to QEMU). No need to expose HV_POST_MESSAGES | HV_SIGNAL_EVENTS. > Is the hyperv_synic_kvm_only check the only reason this was done > here and not at kvm_hyperv_properties? > Yes, basically. > >> + } >> + >> /* Not exposed by KVM but needed to make CPU hotplug in Windows work */ >> c->edx |= HV_CPU_DYNAMIC_PARTITIONING_AVAILABLE; >> >> -- >> 2.31.1 >> -- Vitaly