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Fri, 5 Jun 2020 15:24:09 +0000 (UTC) Date: Fri, 5 Jun 2020 17:24:05 +0200 From: Igor Mammedov To: Andrew Jones Subject: Re: [Question] Regarding PMU initialization within the QEMU for ARM VCPUs Message-ID: <20200605172405.1626979b@redhat.com> In-Reply-To: <20200603102116.hbo4kmaitvh2kofl@kamzik.brq.redhat.com> References: <20200603093745.dwfb55ny34az7rez@kamzik.brq.redhat.com> <20200603102116.hbo4kmaitvh2kofl@kamzik.brq.redhat.com> MIME-Version: 1.0 X-Scanned-By: MIMEDefang 2.84 on 10.5.11.22 X-Mimecast-Spam-Score: 0 X-Mimecast-Originator: redhat.com Content-Type: text/plain; charset=US-ASCII Content-Transfer-Encoding: 7bit Received-SPF: pass client-ip=207.211.31.120; envelope-from=imammedo@redhat.com; helo=us-smtp-1.mimecast.com X-detected-operating-system: by eggs.gnu.org: First seen = 2020/06/05 03:07:04 X-ACL-Warn: Detected OS = Linux 2.2.x-3.x [generic] [fuzzy] 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, DKIMWL_WL_HIGH=0.001, DKIM_SIGNED=0.1, DKIM_VALID=-0.1, DKIM_VALID_AU=-0.1, DKIM_VALID_EF=-0.1, RCVD_IN_DNSWL_NONE=-0.0001, RCVD_IN_MSPIKE_H3=0.001, RCVD_IN_MSPIKE_WL=0.001, SPF_PASS=-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: Peter Maydell , Salil Mehta , "mst@redhat.com" , "qemu-devel@nongnu.org" , Auger Eric , "qemu-arm@nongnu.org" Errors-To: qemu-devel-bounces+qemu-devel=archiver.kernel.org@nongnu.org Sender: "Qemu-devel" On Wed, 3 Jun 2020 12:21:16 +0200 Andrew Jones wrote: > On Wed, Jun 03, 2020 at 11:59:23AM +0200, Auger Eric wrote: > > Hi Drew, > > > > On 6/3/20 11:37 AM, Andrew Jones wrote: > > > On Mon, Jun 01, 2020 at 03:04:33PM +0000, Salil Mehta wrote: > > >> Hello, > > >> I could see below within function fdt_add_pmu_nodes() part of > > >> hw/arm/virt.c during virt machine initialization time: > > >> > > >> Observation: > > >> In below function, support of PMU feature is being checked for > > >> each vcpu and if the PMU is found part of the features then PMU > > >> is initialized with in the host/KVM. But if there is even one > > >> vcpu which is found to not support the PMU then loop is exited > > >> and PMU is not initialized for the rest of the vcpus as well. > > >> > > >> Questions: > > >> Q1. Not sure what is the logic of the premature exit and not > > >> continuing with further checks and initialization of other > > >> VCPU PMUs? > > > > > > KVM requires all VCPUs to have a PMU if one does. > > > > I fail to find where this is enforced? Do you know the place? > > kvm_vcpu_set_target(), called from KVM_ARM_VCPU_INIT. It ensures > all VCPUs have identical features selected. The PMU requires a > VCPU feature (KVM_ARM_VCPU_PMU_V3) to be set. perhaps add a check at cpu_preplug time to ensure that it's so before cpu is create instead of much later FDT initialization? > > Thanks, > drew