Date: Thu, 26 Mar 2026 19:03:36 +0000 From: Alexander Ziaee <ziaee@FreeBSD.org> To: src-committers@FreeBSD.org, dev-commits-src-all@FreeBSD.org, dev-commits-src-main@FreeBSD.org Cc: Matt Delco <delco@google.com> Subject: git: c505fc146884 - main - x86: Guard clock frequency against a divide by 0 Message-ID: <69c58308.195e1.1d1363de@gitrepo.freebsd.org>
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The branch main has been updated by ziaee: URL: https://cgit.FreeBSD.org/src/commit/?id=c505fc1468849150f48484b225b6476d8316de57 commit c505fc1468849150f48484b225b6476d8316de57 Author: Matt Delco <delco@google.com> AuthorDate: 2026-03-26 17:22:54 +0000 Commit: Alexander Ziaee <ziaee@FreeBSD.org> CommitDate: 2026-03-26 19:02:06 +0000 x86: Guard clock frequency against a divide by 0 We may be running in a Virtual Machine which may not fully support hardware performance counters. If the MPERF counter somehow ends up at zero, return an error and fail gracefully instead of panicking. This patch is part of Google Cloud Engine (GCE) C4-LSSD turnup. Sponsored by: Google Tested by: NetApp (previous) PR: 292808 MFC after: 3 days Co-authored-by: Aymeric Wibo <obiwac@google.com> Co-authored-by: Jim Mattson <jmattson@google.com> Suggested by: jrtc27 (split out this part) Reviewed by: imp, obiwac, olce Differential Revision: https://reviews.freebsd.org/D56056 --- sys/x86/x86/cpu_machdep.c | 9 ++++++++- 1 file changed, 8 insertions(+), 1 deletion(-) diff --git a/sys/x86/x86/cpu_machdep.c b/sys/x86/x86/cpu_machdep.c index 5483fbd6dd4e..775fee97d3cd 100644 --- a/sys/x86/x86/cpu_machdep.c +++ b/sys/x86/x86/cpu_machdep.c @@ -425,6 +425,7 @@ cpu_est_clockrate(int cpu_id, uint64_t *rate) uint64_t tsc1, tsc2; uint64_t acnt, mcnt, perf; register_t reg; + int error = 0; if (pcpu_find(cpu_id) == NULL || rate == NULL) return (EINVAL); @@ -460,6 +461,11 @@ cpu_est_clockrate(int cpu_id, uint64_t *rate) acnt = rdmsr(MSR_APERF); tsc2 = rdtsc(); intr_restore(reg); + if (mcnt == 0) { + tsc_perf_stat = 0; + error = EOPNOTSUPP; + goto err; + } perf = 1000 * acnt / mcnt; *rate = (tsc2 - tsc1) * perf; } else { @@ -470,6 +476,7 @@ cpu_est_clockrate(int cpu_id, uint64_t *rate) *rate = (tsc2 - tsc1) * 1000; } +err: #ifdef SMP if (smp_cpus > 1) { thread_lock(curthread); @@ -478,7 +485,7 @@ cpu_est_clockrate(int cpu_id, uint64_t *rate) } #endif - return (0); + return (error); } /*home | help
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