linux-kernel - Re: [PATCH V2 2/3] KVM: x86/pmu: Don't pre-set the pmu->global

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Date:   Tue, 10 May 2022 12:37:53 +0800
From:   Like Xu <like.xu.linux@...il.com>
To:     Paolo Bonzini <pbonzini@...hat.com>
Cc:     Jim Mattson <jmattson@...gle.com>,
        Sean Christopherson <seanjc@...gle.com>,
        Vitaly Kuznetsov <vkuznets@...hat.com>,
        Wanpeng Li <wanpengli@...cent.com>,
        Joerg Roedel <joro@...tes.org>, kvm@...r.kernel.org,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH V2 2/3] KVM: x86/pmu: Don't pre-set the pmu->global_ctrl
 when refreshing

From: Like Xu <likexu@...cent.com>

Assigning a value to pmu->global_ctrl just to set the value of
pmu->global_ctrl_mask in a more readable way leaves a side effect of
not conforming to the specification. The value is reset to zero on
Power up and Reset but keeps unchanged on INIT, like an ordinary MSR.

Signed-off-by: Like Xu <likexu@...cent.com>
---
v1 -> v2 Changelog:
- Explicitly add parentheses around;

  arch/x86/kvm/vmx/pmu_intel.c | 5 ++---
  1 file changed, 2 insertions(+), 3 deletions(-)

diff --git a/arch/x86/kvm/vmx/pmu_intel.c b/arch/x86/kvm/vmx/pmu_intel.c
index cff03baf8921..7945e97db0af 100644
--- a/arch/x86/kvm/vmx/pmu_intel.c
+++ b/arch/x86/kvm/vmx/pmu_intel.c
@@ -525,9 +525,8 @@ static void intel_pmu_refresh(struct kvm_vcpu *vcpu)
          setup_fixed_pmc_eventsel(pmu);
      }

-    pmu->global_ctrl = ((1ull << pmu->nr_arch_gp_counters) - 1) |
-        (((1ull << pmu->nr_arch_fixed_counters) - 1) << INTEL_PMC_IDX_FIXED);
-    pmu->global_ctrl_mask = ~pmu->global_ctrl;
+    pmu->global_ctrl_mask = ~(((1ull << pmu->nr_arch_gp_counters) - 1) |
+        (((1ull << pmu->nr_arch_fixed_counters) - 1) << INTEL_PMC_IDX_FIXED));
      pmu->global_ovf_ctrl_mask = pmu->global_ctrl_mask
              & ~(MSR_CORE_PERF_GLOBAL_OVF_CTRL_OVF_BUF |
                  MSR_CORE_PERF_GLOBAL_OVF_CTRL_COND_CHGD);
-- 
2.36.1