linux-kernel - [PATCH v2 1/3] KVM: x86/pmu: Stop adding speculative Intel GP PMCs that don't exist yet

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Date:   Wed,  7 Sep 2022 18:48:36 +0800
From:   Like Xu <like.xu.linux@...il.com>
To:     Sean Christopherson <seanjc@...gle.com>,
        Paolo Bonzini <pbonzini@...hat.com>
Cc:     kvm@...r.kernel.org, linux-kernel@...r.kernel.org,
        Vitaly Kuznetsov <vkuznets@...hat.com>,
        Jim Mattson <jmattson@...gle.com>
Subject: [PATCH v2 1/3] KVM: x86/pmu: Stop adding speculative Intel GP PMCs that don't exist yet

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

The Intel April 2022 SDM - Table 2-2. IA-32 Architectural MSRs adds
a new architectural IA32_OVERCLOCKING_STATUS msr (0x195), plus the
presence of IA32_CORE_CAPABILITIES (0xCF), the theoretical effective
maximum value of the Intel GP PMCs is 14 (0xCF - 0xC1) instead of 18.

But the conclusion of this speculation "14" is very fragile and can
easily be overturned once Intel declares another meaningful arch msr
in the above reserved range, and even worse, Intel probably put PMCs
8-15 in a completely different range of MSR indices.

A conservative proposal would be to stop at the maximum number of Intel
GP PMCs supported today. Also subsequent changes would limit both AMD
and Intel on the number of GP counter supported by KVM.

There are some boxes like Intel P4 may indeed have 18 counters, but
those counters are in a completely different msr address range and do
not strictly adhere to the Intel Arch PMU specification, and will not
be supported by KVM in the near future.

Cc: Vitaly Kuznetsov <vkuznets@...hat.com>
Suggested-by: Jim Mattson <jmattson@...gle.com>
Signed-off-by: Like Xu <likexu@...cent.com>
---
Previous:
https://lore.kernel.org/kvm/20220906081604.24035-1-likexu@tencent.com/
V1 -> V2 Changelog:
- Stop at the maximum number of GP PMCs supported today; (Jim)

 arch/x86/kvm/x86.c | 14 ++------------
 1 file changed, 2 insertions(+), 12 deletions(-)

diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c
index 43a6a7efc6ec..884f6de11a33 100644
--- a/arch/x86/kvm/x86.c
+++ b/arch/x86/kvm/x86.c
@@ -1428,20 +1428,10 @@ static const u32 msrs_to_save_all[] = {
 	MSR_ARCH_PERFMON_PERFCTR0 + 2, MSR_ARCH_PERFMON_PERFCTR0 + 3,
 	MSR_ARCH_PERFMON_PERFCTR0 + 4, MSR_ARCH_PERFMON_PERFCTR0 + 5,
 	MSR_ARCH_PERFMON_PERFCTR0 + 6, MSR_ARCH_PERFMON_PERFCTR0 + 7,
-	MSR_ARCH_PERFMON_PERFCTR0 + 8, MSR_ARCH_PERFMON_PERFCTR0 + 9,
-	MSR_ARCH_PERFMON_PERFCTR0 + 10, MSR_ARCH_PERFMON_PERFCTR0 + 11,
-	MSR_ARCH_PERFMON_PERFCTR0 + 12, MSR_ARCH_PERFMON_PERFCTR0 + 13,
-	MSR_ARCH_PERFMON_PERFCTR0 + 14, MSR_ARCH_PERFMON_PERFCTR0 + 15,
-	MSR_ARCH_PERFMON_PERFCTR0 + 16, MSR_ARCH_PERFMON_PERFCTR0 + 17,
 	MSR_ARCH_PERFMON_EVENTSEL0, MSR_ARCH_PERFMON_EVENTSEL1,
 	MSR_ARCH_PERFMON_EVENTSEL0 + 2, MSR_ARCH_PERFMON_EVENTSEL0 + 3,
 	MSR_ARCH_PERFMON_EVENTSEL0 + 4, MSR_ARCH_PERFMON_EVENTSEL0 + 5,
 	MSR_ARCH_PERFMON_EVENTSEL0 + 6, MSR_ARCH_PERFMON_EVENTSEL0 + 7,
-	MSR_ARCH_PERFMON_EVENTSEL0 + 8, MSR_ARCH_PERFMON_EVENTSEL0 + 9,
-	MSR_ARCH_PERFMON_EVENTSEL0 + 10, MSR_ARCH_PERFMON_EVENTSEL0 + 11,
-	MSR_ARCH_PERFMON_EVENTSEL0 + 12, MSR_ARCH_PERFMON_EVENTSEL0 + 13,
-	MSR_ARCH_PERFMON_EVENTSEL0 + 14, MSR_ARCH_PERFMON_EVENTSEL0 + 15,
-	MSR_ARCH_PERFMON_EVENTSEL0 + 16, MSR_ARCH_PERFMON_EVENTSEL0 + 17,
 	MSR_IA32_PEBS_ENABLE, MSR_IA32_DS_AREA, MSR_PEBS_DATA_CFG,
 
 	MSR_K7_EVNTSEL0, MSR_K7_EVNTSEL1, MSR_K7_EVNTSEL2, MSR_K7_EVNTSEL3,
@@ -6943,12 +6933,12 @@ static void kvm_init_msr_list(void)
 				intel_pt_validate_hw_cap(PT_CAP_num_address_ranges) * 2)
 				continue;
 			break;
-		case MSR_ARCH_PERFMON_PERFCTR0 ... MSR_ARCH_PERFMON_PERFCTR0 + 17:
+		case MSR_ARCH_PERFMON_PERFCTR0 ... MSR_ARCH_PERFMON_PERFCTR0 + 7:
 			if (msrs_to_save_all[i] - MSR_ARCH_PERFMON_PERFCTR0 >=
 			    min(INTEL_PMC_MAX_GENERIC, kvm_pmu_cap.num_counters_gp))
 				continue;
 			break;
-		case MSR_ARCH_PERFMON_EVENTSEL0 ... MSR_ARCH_PERFMON_EVENTSEL0 + 17:
+		case MSR_ARCH_PERFMON_EVENTSEL0 ... MSR_ARCH_PERFMON_EVENTSEL0 + 7:
 			if (msrs_to_save_all[i] - MSR_ARCH_PERFMON_EVENTSEL0 >=
 			    min(INTEL_PMC_MAX_GENERIC, kvm_pmu_cap.num_counters_gp))
 				continue;
-- 
2.37.3