On 11.06.2021 09:50, Borislav Petkov wrote:

On Wed, Jun 09, 2021 at 02:12:38PM -0700, Pawan Gupta wrote:

quoted

Earlier workaround added by commit 400816f60c54 ("perf/x86/intel:
Implement support for TSX Force Abort") for perf counter interactions
[1] are not required on some client systems which received a microcode
update that deprecates TSX.

Bypass the perf workaround when such microcode is enumerated.

[1] Performance Monitoring Impact of Intel® Transactional Synchronization Extension Memory
    http://cdrdv2.intel.com/v1/dl/getContent/604224

Signed-off-by: Pawan Gupta <pawan.kumar.gupta@linux.intel.com>
Reviewed-by: Andi Kleen <redacted>
Reviewed-by: Tony Luck <tony.luck@intel.com>
Tested-by: Neelima Krishnan <redacted>
---
 arch/x86/events/intel/core.c | 22 ++++++++++++++++++----
 1 file changed, 18 insertions(+), 4 deletions(-)

diff --git a/arch/x86/events/intel/core.c b/arch/x86/events/intel/core.c
index e28892270c58..b5953e1e59a2 100644
--- a/arch/x86/events/intel/core.c
+++ b/arch/x86/events/intel/core.c

@@ -6016,10 +6016,24 @@ __init int intel_pmu_init(void)
 		intel_pmu_pebs_data_source_skl(pmem);

 		if (boot_cpu_has(X86_FEATURE_TSX_FORCE_ABORT)) {
-			x86_pmu.flags |= PMU_FL_TFA;
-			x86_pmu.get_event_constraints = tfa_get_event_constraints;
-			x86_pmu.enable_all = intel_tfa_pmu_enable_all;
-			x86_pmu.commit_scheduling = intel_tfa_commit_scheduling;
+			u64 msr;
+
+			rdmsrl(MSR_TSX_FORCE_ABORT, msr);
+			/* Systems that enumerate CPUID.RTM_ALWAYS_ABORT or
+			 * support MSR_TSX_FORCE_ABORT[SDV_ENABLE_RTM] bit have
+			 * TSX deprecated by default. TSX force abort hooks are
+			 * not required on these systems.

So if they're not required, why aren't you simply disabling the force
abort "workaround" by clearing the feature flag?

Feature flag also enumerates MSR_TSX_FORCE_ABORT, which is still present
after the microcode update. Patch 3/4 in this series clears the TSX
CPUID bits using MSR_TSX_FORCE_ABORT. So we do need the feature flag 
X86_FEATURE_TSX_FORCE_ABORT.

if (boot_cpu_has(X86_FEATURE_TSX_FORCE_ABORT)) {
	if (boot_cpu_has(X86_FEATURE_RTM_ALWAYS_ABORT))
		setup_clear_cpu_cap(X86_FEATURE_TSX_FORCE_ABORT);
}

so that it doesn't get enabled in the first place?

Feature flag is needed as explained above.

Thanks,
Pawan