perf/x86: Avoid touching LBR_TOS MSR for Arch LBR

The Architecture LBR does not have MSR_LBR_TOS (0x000001c9).
In a guest that should support Architecture LBR, check_msr()
will be a non-related check for the architecture MSR 0x0
(IA32_P5_MC_ADDR) that is also not supported by KVM.

The failure will cause x86_pmu.lbr_nr = 0, thereby preventing
the initialization of the guest Arch LBR. Fix it by avoiding
this extraneous check in intel_pmu_init() for Arch LBR.

Fixes: 47125db27e47 ("perf/x86/intel/lbr: Support Architectural LBR")
Signed-off-by: Like Xu <like.xu@linux.intel.com>
[peterz: simpler still]
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Link: https://lkml.kernel.org/r/20210430052247.3079672-1-like.xu@linux.intel.com

diff --git a/arch/x86/events/intel/core.c b/arch/x86/events/intel/core.c
index 2521d03..e288922 100644 (file)
--- a/arch/x86/events/intel/core.c
+++ b/arch/x86/events/intel/core.c
@@ -6253,7 +6253,7 @@ __init int intel_pmu_init(void)
         * Check all LBT MSR here.
         * Disable LBR access if any LBR MSRs can not be accessed.
         */
-       if (x86_pmu.lbr_nr && !check_msr(x86_pmu.lbr_tos, 0x3UL))
+       if (x86_pmu.lbr_tos && !check_msr(x86_pmu.lbr_tos, 0x3UL))
                x86_pmu.lbr_nr = 0;
        for (i = 0; i < x86_pmu.lbr_nr; i++) {
                if (!(check_msr(x86_pmu.lbr_from + i, 0xffffUL) &&