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Tue, 25 Aug 2026 01:37:44 -0700 (PDT) From: SeungJu Cheon To: Anup Patel , Atish Patra Cc: Paul Walmsley , Palmer Dabbelt , Albert Ou , Alexandre Ghiti , Andrew Jones , kvm@vger.kernel.org, kvm-riscv@lists.infradead.org, linux-riscv@lists.infradead.org, linux-kernel@vger.kernel.org, Shuah Khan , linux-kernel-mentees@lists.linux.dev, me@brighamcampbell.com, SeungJu Cheon Subject: [PATCH v1 1/3] RISC-V: KVM: Preserve firmware counter value across stop/start Date: Tue, 25 Aug 2026 17:37:17 +0900 Message-ID: <20260825083719.643970-2-suunj1331@gmail.com> X-Mailer: git-send-email 2.52.0 In-Reply-To: <20260825083719.643970-1-suunj1331@gmail.com> References: <20260825083719.643970-1-suunj1331@gmail.com> Precedence: bulk X-Mailing-List: linux-kernel-mentees@lists.linux.dev List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Transfer-Encoding: 8bit Firmware events accumulate in kvpmu->fw_event[].value while running, but counter stop only clears fw_event[].started without saving the value back to pmc->counter_val. A subsequent counter start without SBI_PMU_START_FLAG_SET_INIT_VALUE reloads the stale counter_val into fw_event[].value, losing all events counted so far. Save fw_event[].value into counter_val when actually stopping a running counter, and remove the now redundant synchronization from the snapshot path. Fixes: badc386869e2c ("RISC-V: KVM: Support firmware events") Signed-off-by: SeungJu Cheon --- arch/riscv/kvm/vcpu_pmu.c | 12 ++++++------ 1 file changed, 6 insertions(+), 6 deletions(-) diff --git a/arch/riscv/kvm/vcpu_pmu.c b/arch/riscv/kvm/vcpu_pmu.c index 2025b664961c..56dd5b1b2846 100644 --- a/arch/riscv/kvm/vcpu_pmu.c +++ b/arch/riscv/kvm/vcpu_pmu.c @@ -671,10 +671,12 @@ int kvm_riscv_vcpu_pmu_ctr_stop(struct kvm_vcpu *vcpu, unsigned long ctr_base, goto out; } - if (!kvpmu->fw_event[fevent_code].started) + if (!kvpmu->fw_event[fevent_code].started) { sbiret = SBI_ERR_ALREADY_STOPPED; - - kvpmu->fw_event[fevent_code].started = false; + } else { + kvpmu->fw_event[fevent_code].started = false; + pmc->counter_val = kvpmu->fw_event[fevent_code].value; + } } else if (pmc->perf_event) { if (pmc->started) { /* Stop counting the counter */ @@ -692,9 +694,7 @@ int kvm_riscv_vcpu_pmu_ctr_stop(struct kvm_vcpu *vcpu, unsigned long ctr_base, } if (snap_flag_set && !sbiret) { - if (pmc->cinfo.type == SBI_PMU_CTR_TYPE_FW) - pmc->counter_val = kvpmu->fw_event[fevent_code].value; - else if (pmc->perf_event) + if (pmc->perf_event) pmc->counter_val += perf_event_read_value(pmc->perf_event, &enabled, &running); /* -- 2.52.0