From b2c04fc1239062b39ddfdd8731ee1a10810dfb74 Mon Sep 17 00:00:00 2001 From: Thomas Richter Date: Fri, 23 Jan 2026 10:14:12 +0100 Subject: [PATCH] s390/perf: Disable register readout on sampling events Running commands # ./perf record -IR0,R1 -a sleep 1 extracts and displays register value of general purpose register r1 and r0. However the value displayed of any register is random and does not reflect the register value recorded at the time of the sample interrupt. The sampling device driver on s390 creates a very large buffer for the hardware to store the samples. Only when that large buffer gets full an interrupt is generated and many hundreds of sample entries are processed and copied to the kernel ring buffer and eventually get copied to the perf tool. It is during the copy to the kernel ring buffer that each sample is processed (on s390) and at that time the register values are extracted. This is not the original goal, the register values should be read when the samples are created not when the samples are copied to the kernel ring buffer. Prevent this event from being installed in the first place and return -EOPNOTSUPP. This is already the case for PERF_SAMPLE_REGS_USER. Signed-off-by: Thomas Richter Reviewed-by: Jan Polensky Signed-off-by: Heiko Carstens --- arch/s390/kernel/perf_cpum_sf.c | 2 +- 1 file changed, 1 insertion(+), 1 deletion(-) diff --git a/arch/s390/kernel/perf_cpum_sf.c b/arch/s390/kernel/perf_cpum_sf.c index 459af23a47a5e..e8bd19ac82c7d 100644 --- a/arch/s390/kernel/perf_cpum_sf.c +++ b/arch/s390/kernel/perf_cpum_sf.c @@ -841,7 +841,7 @@ static bool is_callchain_event(struct perf_event *event) u64 sample_type = event->attr.sample_type; return sample_type & (PERF_SAMPLE_CALLCHAIN | PERF_SAMPLE_REGS_USER | - PERF_SAMPLE_STACK_USER); + PERF_SAMPLE_REGS_INTR | PERF_SAMPLE_STACK_USER); } static int cpumsf_pmu_event_init(struct perf_event *event) -- 2.47.3