linux-kernel - Re: [PATCH v8 07/26] KVM: x86/pmu: Apply "fast" RDPMC only to Intel PMUs

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Message-ID: <5d0c1946-0b22-4983-868b-db7f79fe16bc@linux.intel.com>
Date:   Fri, 10 Nov 2023 11:22:13 +0800
From:   "Mi, Dapeng" <dapeng1.mi@...ux.intel.com>
To:     Sean Christopherson <seanjc@...gle.com>,
        Paolo Bonzini <pbonzini@...hat.com>
Cc:     kvm@...r.kernel.org, linux-kernel@...r.kernel.org,
        Kan Liang <kan.liang@...ux.intel.com>,
        Jim Mattson <jmattson@...gle.com>,
        Jinrong Liang <cloudliang@...cent.com>,
        Aaron Lewis <aaronlewis@...gle.com>,
        Like Xu <likexu@...cent.com>
Subject: Re: [PATCH v8 07/26] KVM: x86/pmu: Apply "fast" RDPMC only to Intel
 PMUs


On 11/10/2023 10:12 AM, Sean Christopherson wrote:
> Move the handling of "fast" RDPMC instructions, which drop bits 63:31 of


63:32?


> the count, to Intel.  The "fast" flag, and all flags for that matter, are
> Intel-only and aren't supported by AMD.
>
> Opportunistically replace open coded bit crud with proper #defines.
>
> Fixes: ca724305a2b0 ("KVM: x86/vPMU: Implement AMD vPMU code for KVM")
> Signed-off-by: Sean Christopherson <seanjc@...gle.com>
> ---
>   arch/x86/kvm/pmu.c           |  3 +--
>   arch/x86/kvm/vmx/pmu_intel.c | 20 ++++++++++++++++----
>   2 files changed, 17 insertions(+), 6 deletions(-)
>
> diff --git a/arch/x86/kvm/pmu.c b/arch/x86/kvm/pmu.c
> index 99ed72966528..e3ba5e12c2e7 100644
> --- a/arch/x86/kvm/pmu.c
> +++ b/arch/x86/kvm/pmu.c
> @@ -499,10 +499,9 @@ static int kvm_pmu_rdpmc_vmware(struct kvm_vcpu *vcpu, unsigned idx, u64 *data)
>   
>   int kvm_pmu_rdpmc(struct kvm_vcpu *vcpu, unsigned idx, u64 *data)
>   {
> -	bool fast_mode = idx & (1u << 31);
>   	struct kvm_pmu *pmu = vcpu_to_pmu(vcpu);
>   	struct kvm_pmc *pmc;
> -	u64 mask = fast_mode ? ~0u : ~0ull;
> +	u64 mask = ~0ull;
>   
>   	if (!pmu->version)
>   		return 1;
> diff --git a/arch/x86/kvm/vmx/pmu_intel.c b/arch/x86/kvm/vmx/pmu_intel.c
> index 3bac3b32b485..c6ea128ea7c8 100644
> --- a/arch/x86/kvm/vmx/pmu_intel.c
> +++ b/arch/x86/kvm/vmx/pmu_intel.c
> @@ -20,6 +20,10 @@
>   #include "nested.h"
>   #include "pmu.h"
>   
> +/* Perf's "BASE" is wildly misleading, this is a single-bit flag, not a base. */
> +#define INTEL_RDPMC_FIXED	INTEL_PMC_FIXED_RDPMC_BASE
> +#define INTEL_RDPMC_FAST	BIT(31)
> +
>   #define MSR_PMC_FULL_WIDTH_BIT      (MSR_IA32_PMC0 - MSR_IA32_PERFCTR0)
>   
>   static void reprogram_fixed_counters(struct kvm_pmu *pmu, u64 data)
> @@ -55,12 +59,17 @@ static struct kvm_pmc *intel_pmc_idx_to_pmc(struct kvm_pmu *pmu, int pmc_idx)
>   	}
>   }
>   
> +static u32 intel_rdpmc_get_masked_idx(struct kvm_pmu *pmu, u32 idx)


inline?


> +{
> +	return idx & ~(INTEL_RDPMC_FIXED | INTEL_RDPMC_FAST);
> +}
> +
>   static bool intel_is_valid_rdpmc_ecx(struct kvm_vcpu *vcpu, unsigned int idx)
>   {
>   	struct kvm_pmu *pmu = vcpu_to_pmu(vcpu);
> -	bool fixed = idx & (1u << 30);
> +	bool fixed = idx & INTEL_RDPMC_FIXED;
>   
> -	idx &= ~(3u << 30);
> +	idx = intel_rdpmc_get_masked_idx(pmu, idx);
>   
>   	return fixed ? idx < pmu->nr_arch_fixed_counters
>   		     : idx < pmu->nr_arch_gp_counters;
> @@ -70,11 +79,14 @@ static struct kvm_pmc *intel_rdpmc_ecx_to_pmc(struct kvm_vcpu *vcpu,
>   					    unsigned int idx, u64 *mask)
>   {
>   	struct kvm_pmu *pmu = vcpu_to_pmu(vcpu);
> -	bool fixed = idx & (1u << 30);
> +	bool fixed = idx & INTEL_RDPMC_FIXED;
>   	struct kvm_pmc *counters;
>   	unsigned int num_counters;
>   
> -	idx &= ~(3u << 30);
> +	if (idx & INTEL_RDPMC_FAST)
> +		*mask &= GENMASK_ULL(31, 0);
> +
> +	idx = intel_rdpmc_get_masked_idx(pmu, idx);
>   	if (fixed) {
>   		counters = pmu->fixed_counters;
>   		num_counters = pmu->nr_arch_fixed_counters;
Reviewed-by: Dapeng Mi <dapeng1.mi@...ux.intel.com>