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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@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Transfer-Encoding: quoted-printable Content-Type: text/plain; charset="utf-8" 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 Reviewed-by: Anup Patel --- 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; } =20 - if (!kvpmu->fw_event[fevent_code].started) + if (!kvpmu->fw_event[fevent_code].started) { sbiret =3D SBI_ERR_ALREADY_STOPPED; - - kvpmu->fw_event[fevent_code].started =3D false; + } else { + kvpmu->fw_event[fevent_code].started =3D false; + pmc->counter_val =3D 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, } =20 if (snap_flag_set && !sbiret) { - if (pmc->cinfo.type =3D=3D SBI_PMU_CTR_TYPE_FW) - pmc->counter_val =3D kvpmu->fw_event[fevent_code].value; 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Tue, 25 Aug 2026 01:37:49 -0700 (PDT) Received: from fedora ([61.74.238.173]) by smtp.gmail.com with ESMTPSA id 41be03b00d2f7-cc199e60abbsm1835887a12.23.2026.08.25.01.37.46 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Tue, 25 Aug 2026 01:37:48 -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 2/3] RISC-V: KVM: Report snapshot write failure to the guest Date: Tue, 25 Aug 2026 17:37:18 +0900 Message-ID: <20260825083719.643970-3-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@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Transfer-Encoding: quoted-printable Content-Type: text/plain; charset="utf-8" If kvm_vcpu_write_guest() fails while updating the PMU snapshot area on counter stop, the guest may receive SBI_SUCCESS without the snapshot being updated, leaving stale data in shared memory. Return SBI_ERR_FAILURE when the snapshot write fails. Fixes: c2f41ddbcdd7 ("RISC-V: KVM: Implement SBI PMU Snapshot feature") Signed-off-by: SeungJu Cheon Reviewed-by: Anup Patel --- arch/riscv/kvm/vcpu_pmu.c | 7 ++++--- 1 file changed, 4 insertions(+), 3 deletions(-) diff --git a/arch/riscv/kvm/vcpu_pmu.c b/arch/riscv/kvm/vcpu_pmu.c index 56dd5b1b2846..45dd5233340d 100644 --- a/arch/riscv/kvm/vcpu_pmu.c +++ b/arch/riscv/kvm/vcpu_pmu.c @@ -723,9 +723,10 @@ int kvm_riscv_vcpu_pmu_ctr_stop(struct kvm_vcpu *vcpu,= unsigned long ctr_base, } } =20 - if (shmem_needs_update) - kvm_vcpu_write_guest(vcpu, kvpmu->snapshot_addr, kvpmu->sdata, - sizeof(struct riscv_pmu_snapshot_data)); + if (shmem_needs_update && + kvm_vcpu_write_guest(vcpu, kvpmu->snapshot_addr, kvpmu->sdata, + sizeof(struct riscv_pmu_snapshot_data))) + sbiret =3D SBI_ERR_FAILURE; =20 out: retdata->err_val =3D sbiret; --=20 2.52.0 From nobody Mon Sep 28 07:17:18 2026 Received: from mail-pg1-f169.google.com (mail-pg1-f169.google.com [209.85.215.169]) (using TLSv1.2 with cipher ECDHE-RSA-AES128-GCM-SHA256 (128/128 bits)) (No client certificate requested) by smtp.subspace.kernel.org (Postfix) with ESMTPS id ACF4F3E63A2 for ; 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Tue, 25 Aug 2026 01:37:54 -0700 (PDT) Received: from fedora ([61.74.238.173]) by smtp.gmail.com with ESMTPSA id 41be03b00d2f7-cc199e60abbsm1835887a12.23.2026.08.25.01.37.51 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Tue, 25 Aug 2026 01:37:54 -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 3/3] RISC-V: KVM: Fix perf-backed counter accounting across stop and read Date: Tue, 25 Aug 2026 17:37:19 +0900 Message-ID: <20260825083719.643970-4-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@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Transfer-Encoding: quoted-printable Content-Type: text/plain; charset="utf-8" pmu_ctr_read() adds the event count returned by perf_event_read_value() to counter_val, which can accumulate the same count repeatedly across reads. kvm_riscv_vcpu_pmu_ctr_stop() also leaves counter_val stale by not folding the current event count into it. Make reads of perf-backed counters side-effect free, and use perf_event_pause() when stopping a counter to fold the current event count into counter_val while resetting it. This preserves the counter value across stop/start and lets the snapshot path use counter_val directly. Fixes: 0cb74b65d2e5 ("RISC-V: KVM: Implement perf support without sampling") Signed-off-by: SeungJu Cheon Reviewed-by: Anup Patel --- arch/riscv/kvm/vcpu_pmu.c | 16 ++++++++-------- 1 file changed, 8 insertions(+), 8 deletions(-) diff --git a/arch/riscv/kvm/vcpu_pmu.c b/arch/riscv/kvm/vcpu_pmu.c index 45dd5233340d..7d50490cc622 100644 --- a/arch/riscv/kvm/vcpu_pmu.c +++ b/arch/riscv/kvm/vcpu_pmu.c @@ -268,12 +268,13 @@ static int pmu_ctr_read(struct kvm_vcpu *vcpu, unsign= ed long cidx, return -EINVAL; =20 pmc->counter_val =3D kvpmu->fw_event[fevent_code].value; + *out_val =3D pmc->counter_val; } else if (pmc->perf_event) { - pmc->counter_val +=3D perf_event_read_value(pmc->perf_event, &enabled, &= running); + *out_val =3D pmc->counter_val + + perf_event_read_value(pmc->perf_event, &enabled, &running); } else { return -EINVAL; } - *out_val =3D pmc->counter_val; =20 return 0; } @@ -641,7 +642,6 @@ int kvm_riscv_vcpu_pmu_ctr_stop(struct kvm_vcpu *vcpu, = unsigned long ctr_base, { struct kvm_pmu *kvpmu =3D vcpu_to_pmu(vcpu); int i, pmc_index, sbiret =3D 0; - u64 enabled, running; struct kvm_pmc *pmc; int fevent_code; bool snap_flag_set =3D flags & SBI_PMU_STOP_FLAG_TAKE_SNAPSHOT; @@ -679,8 +679,11 @@ int kvm_riscv_vcpu_pmu_ctr_stop(struct kvm_vcpu *vcpu,= unsigned long ctr_base, } } else if (pmc->perf_event) { if (pmc->started) { - /* Stop counting the counter */ - perf_event_disable(pmc->perf_event); + /* + * Stop the counter and fold the live count into counter_val. + * Reset the event value to avoid redundant accumulation. + */ + pmc->counter_val +=3D perf_event_pause(pmc->perf_event, true); pmc->started =3D false; } else { sbiret =3D SBI_ERR_ALREADY_STOPPED; @@ -694,9 +697,6 @@ int kvm_riscv_vcpu_pmu_ctr_stop(struct kvm_vcpu *vcpu, = unsigned long ctr_base, } =20 if (snap_flag_set && !sbiret) { - if (pmc->perf_event) - pmc->counter_val +=3D perf_event_read_value(pmc->perf_event, - &enabled, &running); /* * The counter and overflow indices in the snapshot region are w.r.to * cbase. Modify the set bit in the counter mask instead of the pmc_ind= ex --=20 2.52.0