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From: SeungJu Cheon <suunj1331@gmail.com>
To: Anup Patel <anup@brainfault.org>, Atish Patra <atish.patra@linux.dev>
Cc: Paul Walmsley <pjw@kernel.org>,
	Palmer Dabbelt <palmer@dabbelt.com>,
	Albert Ou <aou@eecs.berkeley.edu>,
	Alexandre Ghiti <alex@ghiti.fr>,
	Andrew Jones <ajones@ventanamicro.com>,
	kvm@vger.kernel.org, kvm-riscv@lists.infradead.org,
	linux-riscv@lists.infradead.org, linux-kernel@vger.kernel.org,
	Shuah Khan <skhan@linuxfoundation.org>,
	linux-kernel-mentees@lists.linux.dev, me@brighamcampbell.com,
	SeungJu Cheon <suunj1331@gmail.com>
Subject: [PATCH v1 1/3] RISC-V: KVM: Preserve firmware counter value across stop/start
Date: Tue, 25 Aug 2026 17:37:17 +0900	[thread overview]
Message-ID: <20260825083719.643970-2-suunj1331@gmail.com> (raw)
In-Reply-To: <20260825083719.643970-1-suunj1331@gmail.com>

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 <suunj1331@gmail.com>
---
 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


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  reply	other threads:[~2026-08-25  8:37 UTC|newest]

Thread overview: 4+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2026-08-25  8:37 [PATCH v1 0/3] RISC-V: KVM: Fix PMU counter handling issues SeungJu Cheon
2026-08-25  8:37 ` SeungJu Cheon [this message]
2026-08-25  8:37 ` [PATCH v1 2/3] RISC-V: KVM: Report snapshot write failure to the guest SeungJu Cheon
2026-08-25  8:37 ` [PATCH v1 3/3] RISC-V: KVM: Fix perf-backed counter accounting across stop and read SeungJu Cheon

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