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([2a01:e0a:59e:9d80:527b:9dff:feef:3874]) by smtp.gmail.com with ESMTPSA id ay21sm1902044wmb.7.2021.12.02.02.57.12 (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Thu, 02 Dec 2021 02:57:12 -0800 (PST) Subject: Re: [RFC PATCH v3 09/29] KVM: arm64: Hide IMPLEMENTATION DEFINED PMU support for the guest To: Reiji Watanabe Cc: kvm@vger.kernel.org, Marc Zyngier , Peter Shier , Paolo Bonzini , Will Deacon , kvmarm@lists.cs.columbia.edu, linux-arm-kernel@lists.infradead.org References: <20211117064359.2362060-1-reijiw@google.com> <20211117064359.2362060-10-reijiw@google.com> From: Eric Auger Message-ID: <5bd01c9c-6ac8-4034-6f49-be636a3b287c@redhat.com> Date: Thu, 2 Dec 2021 11:57:11 +0100 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:78.0) Gecko/20100101 Thunderbird/78.10.1 MIME-Version: 1.0 In-Reply-To: Authentication-Results: relay.mimecast.com; auth=pass smtp.auth=CUSA124A263 smtp.mailfrom=eauger@redhat.com X-Mimecast-Spam-Score: 0 X-Mimecast-Originator: redhat.com Content-Language: en-US X-CRM114-Version: 20100106-BlameMichelson ( TRE 0.8.0 (BSD) ) MR-646709E3 X-CRM114-CacheID: sfid-20211202_025720_522383_677907D9 X-CRM114-Status: GOOD ( 26.80 ) X-BeenThere: linux-arm-kernel@lists.infradead.org X-Mailman-Version: 2.1.34 Precedence: list List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Content-Type: text/plain; charset="us-ascii" Content-Transfer-Encoding: 7bit Sender: "linux-arm-kernel" Errors-To: linux-arm-kernel-bounces+linux-arm-kernel=archiver.kernel.org@lists.infradead.org Hi Reiji, On 11/30/21 6:32 AM, Reiji Watanabe wrote: > Hi Eric, > > On Thu, Nov 25, 2021 at 12:30 PM Eric Auger wrote: >> >> Hi Reiji, >> >> On 11/17/21 7:43 AM, Reiji Watanabe wrote: >>> When ID_AA64DFR0_EL1.PMUVER or ID_DFR0_EL1.PERFMON is 0xf, which >>> means IMPLEMENTATION DEFINED PMU supported, KVM unconditionally >>> expose the value for the guest as it is. Since KVM doesn't support >>> IMPLEMENTATION DEFINED PMU for the guest, in that case KVM should >>> exopse 0x0 (PMU is not implemented) instead. >> s/exopse/expose >>> >>> Change cpuid_feature_cap_perfmon_field() to update the field value >>> to 0x0 when it is 0xf. >> is it wrong to expose the guest with a Perfmon value of 0xF? Then the >> guest should not use it as a PMUv3? > >> is it wrong to expose the guest with a Perfmon value of 0xF? Then the >> guest should not use it as a PMUv3? > > For the value 0xf in ID_AA64DFR0_EL1.PMUVER and ID_DFR0_EL1.PERFMON, > Arm ARM says: > "IMPLEMENTATION DEFINED form of performance monitors supported, > PMUv3 not supported." > > Since the PMU that KVM supports for guests is PMUv3, 0xf shouldn't > be exposed to guests (And this patch series doesn't allow userspace > to set the fields to 0xf for guests). What I don't get is why this isn't detected before (in kvm_reset_vcpu). if the VCPU was initialized with KVM_ARM_VCPU_PMU_V3 can we honor this init request if the host pmu is implementation defined? Thanks Eric > > Thanks, > Reiji > >> >> Eric >>> >>> Fixes: 8e35aa642ee4 ("arm64: cpufeature: Extract capped perfmon fields") >>> Signed-off-by: Reiji Watanabe >>> --- >>> arch/arm64/include/asm/cpufeature.h | 2 +- >>> 1 file changed, 1 insertion(+), 1 deletion(-) >>> >>> diff --git a/arch/arm64/include/asm/cpufeature.h b/arch/arm64/include/asm/cpufeature.h >>> index ef6be92b1921..fd7ad8193827 100644 >>> --- a/arch/arm64/include/asm/cpufeature.h >>> +++ b/arch/arm64/include/asm/cpufeature.h >>> @@ -553,7 +553,7 @@ cpuid_feature_cap_perfmon_field(u64 features, int field, u64 cap) >>> >>> /* Treat IMPLEMENTATION DEFINED functionality as unimplemented */ >>> if (val == ID_AA64DFR0_PMUVER_IMP_DEF) >>> - val = 0; >>> + return (features & ~mask); >>> >>> if (val > cap) { >>> features &= ~mask; >>> >> > _______________________________________________ > kvmarm mailing list > kvmarm@lists.cs.columbia.edu > https://lists.cs.columbia.edu/mailman/listinfo/kvmarm > _______________________________________________ linux-arm-kernel mailing list linux-arm-kernel@lists.infradead.org http://lists.infradead.org/mailman/listinfo/linux-arm-kernel