perf/x86/amd/core: Always use the NMI latency mitigation

commit 73a4c02f94a98d94480c3e5c81450215a4da05ba upstream.

Commit df4d29732fda ("perf/x86/amd: Change/fix NMI latency mitigation
to use a timestamp") fixed handling of late-arriving NMIs but limited
the mitigation to processors having X86_FEATURE_PERFCTR_CORE. However,
it is unclear if processors without this feature are also affected.
When Mediated vPMU is enabled on affected hardware, it is also possible
to bypass the fix inside KVM guests if X86_FEATURE_PERFCTR_CORE is
removed from the guest CPUID (e.g. using "-cpu host,-perfctr-core" with
QEMU). Hence, use the mitigation at all times.

Fixes: df4d29732fda ("perf/x86/amd: Change/fix NMI latency mitigation to use a timestamp")
Signed-off-by: Sandipan Das <sandipan.das@amd.com>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Link: https://patch.msgid.link/29a3c970da289ab8f24282933bdb36545c0403e8.1780325517.git.sandipan.das@amd.com
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

diff --git a/arch/x86/events/amd/core.c b/arch/x86/events/amd/core.c
index 5a6ef45dc9b68b5d386afa47300215e25bbf7467..d1f882cf418d4f52f9aad7a5619dbc121a74434a 100644 (file)
--- a/arch/x86/events/amd/core.c
+++ b/arch/x86/events/amd/core.c
@@ -1352,12 +1352,12 @@ static int __init amd_core_pmu_init(void)
        u64 even_ctr_mask = 0ULL;
        int i;
 
-       if (!boot_cpu_has(X86_FEATURE_PERFCTR_CORE))
-               return 0;
-
        /* Avoid calculating the value each time in the NMI handler */
        perf_nmi_window = msecs_to_jiffies(100);
 
+       if (!boot_cpu_has(X86_FEATURE_PERFCTR_CORE))
+               return 0;
+
        /*
         * If core performance counter extensions exists, we must use
         * MSR_F15H_PERF_CTL/MSR_F15H_PERF_CTR msrs. See also