git: 38af24ed0811 - stable/15 - hwpmc: fix event allocation on pre-Zen AMD CPUs

The branch stable/15 has been updated by olivier:

URL: https://cgit.FreeBSD.org/src/commit/?id=38af24ed0811c5ab693096cbb9e57ef29892afa3

commit 38af24ed0811c5ab693096cbb9e57ef29892afa3
Author:     Olivier Cochard <olivier@FreeBSD.org>
AuthorDate: 2026-07-28 19:06:27 +0000
Commit:     Olivier Cochard <olivier@FreeBSD.org>
CommitDate: 2026-08-04 09:28:08 +0000

    hwpmc: fix event allocation on pre-Zen AMD CPUs
    
    amd_allocate_pmc() chose the pmu-events code path whenever pmc_cpuid was
    non-empty, and rejected any allocation lacking PMC_F_EV_PMU.
    But pmc_cpuid is set for every AMD CPU, while the pmu-events tables only cover
    Zen and later.
    On older families (K8, Bobcat, Jaguar/16h, Bulldozer) libpmc finds no
    pmu-events entry and falls back to the legacy path, which never sets
    PMC_F_EV_PMU.
    
    Reviewed by:    mhorne
    Approved by:    mhorne
    MFC after:      1 week
    Sponsored by:   Netflix
    Differential Revision:  https://reviews.freebsd.org/D58468
    
    (cherry picked from commit 6c4d9b9af1a3b247bf82a4228c835d106f535613)
---
 sys/dev/hwpmc/hwpmc_amd.c | 6 ++----
 1 file changed, 2 insertions(+), 4 deletions(-)

diff --git a/sys/dev/hwpmc/hwpmc_amd.c b/sys/dev/hwpmc/hwpmc_amd.c
index 792411ec2033..82d1a4c6180c 100644
--- a/sys/dev/hwpmc/hwpmc_amd.c
+++ b/sys/dev/hwpmc/hwpmc_amd.c
@@ -342,9 +342,6 @@ amd_allocate_pmc(int cpu __unused, int ri, struct pmc *pm,
 	if (pd->pd_class != a->pm_class)
 		return (EINVAL);
 
-	if ((a->pm_flags & PMC_F_EV_PMU) == 0)
-		return (EINVAL);
-
 	caps = pm->pm_caps;
 
 	if (((caps & PMC_CAP_PRECISE) != 0) &&
@@ -357,7 +354,8 @@ amd_allocate_pmc(int cpu __unused, int ri, struct pmc *pm,
 	if (amd_pmcdesc[ri].pm_subclass != a->pm_md.pm_amd.pm_amd_sub_class)
 		return (EINVAL);
 
-	if (strlen(pmc_cpuid) != 0) {
+	/* PMC_F_EV_PMU: config comes from pmu-events tables. */
+	if ((a->pm_flags & PMC_F_EV_PMU) != 0) {
 		pm->pm_md.pm_amd.pm_amd_evsel = a->pm_md.pm_amd.pm_amd_config;
 		PMCDBG2(MDP, ALL, 2,"amd-allocate ri=%d -> config=0x%x", ri,
 		    a->pm_md.pm_amd.pm_amd_config);