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Thu, 05 Mar 2026 05:10:07 -0800 (PST) Message-ID: <208aebfe-3b25-4bf5-8c82-71f323f57847@linaro.org> Date: Thu, 5 Mar 2026 13:10:06 +0000 Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH] KVM: arm64: Read PMUVer as unsigned To: Marc Zyngier Cc: Oliver Upton , Joey Gouly , Suzuki K Poulose , Zenghui Yu , Catalin Marinas , Will Deacon , Colton Lewis , Alexandru Elisei , linux-arm-kernel@lists.infradead.org, kvmarm@lists.linux.dev, linux-kernel@vger.kernel.org References: <20260305-james-kvm-pmuver-sign-v1-1-eea0a2116dd0@linaro.org> <86pl5i7ahj.wl-maz@kernel.org> Content-Language: en-US From: James Clark In-Reply-To: <86pl5i7ahj.wl-maz@kernel.org> Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 7bit On 05/03/2026 11:59 am, Marc Zyngier wrote: > On Thu, 05 Mar 2026 11:50:01 +0000, > James Clark wrote: >> >> ID_AA64DFR0_EL1.PMUVer is an unsigned field, so this skips >> initialization of host_data_ptr(nr_event_counters) for PMUv3 for Armv8.8 >> onwards as they appear as negative values. >> >> Fix it by reading it as unsigned. >> >> Fixes: 2417218f2f23 ("KVM: arm64: Get rid of __kvm_get_mdcr_el2() and related warts") >> Signed-off-by: James Clark >> --- >> arch/arm64/kvm/debug.c | 2 +- >> 1 file changed, 1 insertion(+), 1 deletion(-) >> >> diff --git a/arch/arm64/kvm/debug.c b/arch/arm64/kvm/debug.c >> index 3ad6b7c6e4ba..b8632edba9a3 100644 >> --- a/arch/arm64/kvm/debug.c >> +++ b/arch/arm64/kvm/debug.c >> @@ -76,7 +76,7 @@ void kvm_init_host_debug_data(void) >> { >> u64 dfr0 = read_sysreg(id_aa64dfr0_el1); >> >> - if (cpuid_feature_extract_signed_field(dfr0, ID_AA64DFR0_EL1_PMUVer_SHIFT) > 0) >> + if (cpuid_feature_extract_unsigned_field(dfr0, ID_AA64DFR0_EL1_PMUVer_SHIFT) > 0) >> *host_data_ptr(nr_event_counters) = FIELD_GET(ARMV8_PMU_PMCR_N, >> read_sysreg(pmcr_el0)); >> > > How does this work on a system that advertises a non-architected PMU? > > M. > Hmmm yeah I suppose it doesn't, there's actually already pmuv3_implemented() and has_pmuv3() which open code the same check again. Maybe I can try re-using something and tidying it up.