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Date: Wed, 4 Jan 2023 15:59:04 +0000
From: Sean Christopherson <seanjc@...gle.com>
To: "Yang, Weijiang" <weijiang.yang@...el.com>
Cc: Like Xu <like.xu.linux@...il.com>,
Paolo Bonzini <pbonzini@...hat.com>,
"kvm@...r.kernel.org" <kvm@...r.kernel.org>,
"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
Aaron Lewis <aaronlewis@...gle.com>
Subject: Re: [PATCH 1/3] KVM: x86: Omit PMU MSRs from KVM_GET_MSR_INDEX_LIST
if !enable_pmu
On Tue, Dec 27, 2022, Yang, Weijiang wrote:
>
> On 12/26/2022 7:17 PM, Like Xu wrote:
> > From: Like Xu <likexu@...cent.com>
> >
> > When the PMU is disabled, don't bother sharing the PMU MSRs with
> > userspace through KVM_GET_MSR_INDEX_LIST. Instead, filter them out
> > so userspace doesn't have to keep track of them.
> >
> > Note that 'enable_pmu' is read-only, so userspace has no control over
> > whether the PMU MSRs are included in the list or not.
> >
> > Suggested-by: Sean Christopherson <seanjc@...gle.com>
> > Co-developed-by: Aaron Lewis <aaronlewis@...gle.com>
> > Signed-off-by: Aaron Lewis <aaronlewis@...gle.com>
> > Signed-off-by: Like Xu <likexu@...cent.com>
> > ---
> > arch/x86/include/asm/kvm_host.h | 1 +
> > arch/x86/kvm/x86.c | 22 ++++++++++++++++++++--
> > 2 files changed, 21 insertions(+), 2 deletions(-)
> >
> > diff --git a/arch/x86/include/asm/kvm_host.h b/arch/x86/include/asm/kvm_host.h
> > index f35f1ff4427b..2ed710b393eb 100644
> > --- a/arch/x86/include/asm/kvm_host.h
> > +++ b/arch/x86/include/asm/kvm_host.h
> > @@ -514,6 +514,7 @@ struct kvm_pmc {
> > #define MSR_ARCH_PERFMON_PERFCTR_MAX (MSR_ARCH_PERFMON_PERFCTR0 + KVM_INTEL_PMC_MAX_GENERIC - 1)
> > #define MSR_ARCH_PERFMON_EVENTSEL_MAX (MSR_ARCH_PERFMON_EVENTSEL0 + KVM_INTEL_PMC_MAX_GENERIC - 1)
> > #define KVM_PMC_MAX_FIXED 3
> > +#define MSR_ARCH_PERFMON_FIXED_CTR_MAX (MSR_ARCH_PERFMON_FIXED_CTR0 + KVM_PMC_MAX_FIXED - 1)
> > #define KVM_AMD_PMC_MAX_GENERIC 6
> > struct kvm_pmu {
> > unsigned nr_arch_gp_counters;
> > diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c
> > index 5c3ce39cdccb..f570367463c8 100644
> > --- a/arch/x86/kvm/x86.c
> > +++ b/arch/x86/kvm/x86.c
> > @@ -7054,15 +7054,32 @@ static void kvm_init_msr_list(void)
> > continue;
> > break;
> > case MSR_ARCH_PERFMON_PERFCTR0 ... MSR_ARCH_PERFMON_PERFCTR_MAX:
> > - if (msrs_to_save_all[i] - MSR_ARCH_PERFMON_PERFCTR0 >=
> > + if (!enable_pmu || msrs_to_save_all[i] - MSR_ARCH_PERFMON_PERFCTR0 >=
> > min(KVM_INTEL_PMC_MAX_GENERIC, kvm_pmu_cap.num_counters_gp))
> > continue;
> > break;
> > case MSR_ARCH_PERFMON_EVENTSEL0 ... MSR_ARCH_PERFMON_EVENTSEL_MAX:
> > - if (msrs_to_save_all[i] - MSR_ARCH_PERFMON_EVENTSEL0 >=
> > + if (!enable_pmu || msrs_to_save_all[i] - MSR_ARCH_PERFMON_EVENTSEL0 >=
> > min(KVM_INTEL_PMC_MAX_GENERIC, kvm_pmu_cap.num_counters_gp))
> > continue;
> > break;
> > + case MSR_ARCH_PERFMON_FIXED_CTR0 ... MSR_ARCH_PERFMON_FIXED_CTR_MAX:
> > + if (!enable_pmu || msrs_to_save_all[i] - MSR_ARCH_PERFMON_FIXED_CTR0 >=
> > + min(KVM_PMC_MAX_FIXED, kvm_pmu_cap.num_counters_fixed))
The num_counters_fixed check is a separate change, no?
> > + continue;
> > + break;
> > + case MSR_F15H_PERF_CTL0 ... MSR_F15H_PERF_CTR5:
> > + case MSR_K7_EVNTSEL0 ... MSR_K7_PERFCTR3:
> > + case MSR_CORE_PERF_FIXED_CTR_CTRL:
> > + case MSR_CORE_PERF_GLOBAL_STATUS:
> > + case MSR_CORE_PERF_GLOBAL_CTRL:
> > + case MSR_CORE_PERF_GLOBAL_OVF_CTRL:
> > + case MSR_IA32_DS_AREA:
> > + case MSR_IA32_PEBS_ENABLE:
> > + case MSR_PEBS_DATA_CFG:
Rather than duplicating all list entries, which will be a maintenance problem,
what about moving PMU MSRs to a separate array? Sample patch (that applies on top
of the num_counters_fixed change) at the bottom.
> > + if (!enable_pmu)
> > + continue;
> > + break;
>
>
> I prefer use a helper to wrap the hunk of PMU msr checks and move the helper
> to the "default" branch of switch, it makes the code looks nicer:
>
> default:
That won't work as "default" is used to catch MSRs that always exist from the
guest's perspective. And even if that weren't the case, I don't like the idea of
utilizing "default" for PMU MSRs. The default=>PMU logic in kvm_{g,s}et_msr_common()
isn't ideal, but it's the lesser of all evils. But in this case there's no need
since common KVM code knows all possible MSRs that might be saved.
---
arch/x86/kvm/x86.c | 161 ++++++++++++++++++++++++---------------------
1 file changed, 87 insertions(+), 74 deletions(-)
diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c
index 1cc8036d9e91..87bb7024e18f 100644
--- a/arch/x86/kvm/x86.c
+++ b/arch/x86/kvm/x86.c
@@ -1419,7 +1419,7 @@ EXPORT_SYMBOL_GPL(kvm_emulate_rdpmc);
* may depend on host virtualization features rather than host cpu features.
*/
-static const u32 msrs_to_save_all[] = {
+static const u32 msrs_to_save_base[] = {
MSR_IA32_SYSENTER_CS, MSR_IA32_SYSENTER_ESP, MSR_IA32_SYSENTER_EIP,
MSR_STAR,
#ifdef CONFIG_X86_64
@@ -1436,6 +1436,10 @@ static const u32 msrs_to_save_all[] = {
MSR_IA32_RTIT_ADDR3_A, MSR_IA32_RTIT_ADDR3_B,
MSR_IA32_UMWAIT_CONTROL,
+ MSR_IA32_XFD, MSR_IA32_XFD_ERR,
+};
+
+static const u32 msrs_to_save_pmu[] = {
MSR_ARCH_PERFMON_FIXED_CTR0, MSR_ARCH_PERFMON_FIXED_CTR1,
MSR_ARCH_PERFMON_FIXED_CTR0 + 2,
MSR_CORE_PERF_FIXED_CTR_CTRL, MSR_CORE_PERF_GLOBAL_STATUS,
@@ -1460,11 +1464,10 @@ static const u32 msrs_to_save_all[] = {
MSR_F15H_PERF_CTL3, MSR_F15H_PERF_CTL4, MSR_F15H_PERF_CTL5,
MSR_F15H_PERF_CTR0, MSR_F15H_PERF_CTR1, MSR_F15H_PERF_CTR2,
MSR_F15H_PERF_CTR3, MSR_F15H_PERF_CTR4, MSR_F15H_PERF_CTR5,
-
- MSR_IA32_XFD, MSR_IA32_XFD_ERR,
};
-static u32 msrs_to_save[ARRAY_SIZE(msrs_to_save_all)];
+static u32 msrs_to_save[ARRAY_SIZE(msrs_to_save_base) +
+ ARRAY_SIZE(msrs_to_save_pmu)];
static unsigned num_msrs_to_save;
static const u32 emulated_msrs_all[] = {
@@ -7001,9 +7004,83 @@ long kvm_arch_vm_ioctl(struct file *filp,
return r;
}
-static void kvm_init_msr_list(void)
+static void kvm_probe_msr_to_save(u32 msr_index)
{
u32 dummy[2];
+
+ if (rdmsr_safe(msr_index, &dummy[0], &dummy[1]))
+ return;
+
+ /*
+ * Even MSRs that are valid in the host may not be exposed to the
+ * guests in some cases.
+ */
+ switch (msr_index) {
+ case MSR_IA32_BNDCFGS:
+ if (!kvm_mpx_supported())
+ return;
+ break;
+ case MSR_TSC_AUX:
+ if (!kvm_cpu_cap_has(X86_FEATURE_RDTSCP) &&
+ !kvm_cpu_cap_has(X86_FEATURE_RDPID))
+ return;
+ break;
+ case MSR_IA32_UMWAIT_CONTROL:
+ if (!kvm_cpu_cap_has(X86_FEATURE_WAITPKG))
+ return;
+ break;
+ case MSR_IA32_RTIT_CTL:
+ case MSR_IA32_RTIT_STATUS:
+ if (!kvm_cpu_cap_has(X86_FEATURE_INTEL_PT))
+ return;
+ break;
+ case MSR_IA32_RTIT_CR3_MATCH:
+ if (!kvm_cpu_cap_has(X86_FEATURE_INTEL_PT) ||
+ !intel_pt_validate_hw_cap(PT_CAP_cr3_filtering))
+ return;
+ break;
+ case MSR_IA32_RTIT_OUTPUT_BASE:
+ case MSR_IA32_RTIT_OUTPUT_MASK:
+ if (!kvm_cpu_cap_has(X86_FEATURE_INTEL_PT) ||
+ (!intel_pt_validate_hw_cap(PT_CAP_topa_output) &&
+ !intel_pt_validate_hw_cap(PT_CAP_single_range_output)))
+ return;
+ break;
+ case MSR_IA32_RTIT_ADDR0_A ... MSR_IA32_RTIT_ADDR3_B:
+ if (!kvm_cpu_cap_has(X86_FEATURE_INTEL_PT) ||
+ (msr_index - MSR_IA32_RTIT_ADDR0_A >=
+ intel_pt_validate_hw_cap(PT_CAP_num_address_ranges) * 2))
+ return;
+ break;
+ case MSR_ARCH_PERFMON_PERFCTR0 ... MSR_ARCH_PERFMON_PERFCTR_MAX:
+ if (msr_index - MSR_ARCH_PERFMON_PERFCTR0 >=
+ min(KVM_INTEL_PMC_MAX_GENERIC, kvm_pmu_cap.num_counters_gp))
+ return;
+ break;
+ case MSR_ARCH_PERFMON_EVENTSEL0 ... MSR_ARCH_PERFMON_EVENTSEL_MAX:
+ if (msr_index - MSR_ARCH_PERFMON_EVENTSEL0 >=
+ min(KVM_INTEL_PMC_MAX_GENERIC, kvm_pmu_cap.num_counters_gp))
+ return;
+ break;
+ case MSR_ARCH_PERFMON_FIXED_CTR0 ... MSR_ARCH_PERFMON_FIXED_CTR_MAX:
+ if (msr_index - MSR_ARCH_PERFMON_FIXED_CTR0 >=
+ min(KVM_PMC_MAX_FIXED, kvm_pmu_cap.num_counters_fixed))
+ return;
+ break;
+ case MSR_IA32_XFD:
+ case MSR_IA32_XFD_ERR:
+ if (!kvm_cpu_cap_has(X86_FEATURE_XFD))
+ return;
+ break;
+ default:
+ break;
+ }
+
+ msrs_to_save[num_msrs_to_save++] = msr_index;
+}
+
+static void kvm_init_msr_list(void)
+{
unsigned i;
BUILD_BUG_ON_MSG(KVM_PMC_MAX_FIXED != 3,
@@ -7013,76 +7090,12 @@ static void kvm_init_msr_list(void)
num_emulated_msrs = 0;
num_msr_based_features = 0;
- for (i = 0; i < ARRAY_SIZE(msrs_to_save_all); i++) {
- if (rdmsr_safe(msrs_to_save_all[i], &dummy[0], &dummy[1]) < 0)
- continue;
+ for (i = 0; i < ARRAY_SIZE(msrs_to_save_base); i++)
+ kvm_probe_msr_to_save(msrs_to_save_base[i]);
- /*
- * Even MSRs that are valid in the host may not be exposed
- * to the guests in some cases.
- */
- switch (msrs_to_save_all[i]) {
- case MSR_IA32_BNDCFGS:
- if (!kvm_mpx_supported())
- continue;
- break;
- case MSR_TSC_AUX:
- if (!kvm_cpu_cap_has(X86_FEATURE_RDTSCP) &&
- !kvm_cpu_cap_has(X86_FEATURE_RDPID))
- continue;
- break;
- case MSR_IA32_UMWAIT_CONTROL:
- if (!kvm_cpu_cap_has(X86_FEATURE_WAITPKG))
- continue;
- break;
- case MSR_IA32_RTIT_CTL:
- case MSR_IA32_RTIT_STATUS:
- if (!kvm_cpu_cap_has(X86_FEATURE_INTEL_PT))
- continue;
- break;
- case MSR_IA32_RTIT_CR3_MATCH:
- if (!kvm_cpu_cap_has(X86_FEATURE_INTEL_PT) ||
- !intel_pt_validate_hw_cap(PT_CAP_cr3_filtering))
- continue;
- break;
- case MSR_IA32_RTIT_OUTPUT_BASE:
- case MSR_IA32_RTIT_OUTPUT_MASK:
- if (!kvm_cpu_cap_has(X86_FEATURE_INTEL_PT) ||
- (!intel_pt_validate_hw_cap(PT_CAP_topa_output) &&
- !intel_pt_validate_hw_cap(PT_CAP_single_range_output)))
- continue;
- break;
- case MSR_IA32_RTIT_ADDR0_A ... MSR_IA32_RTIT_ADDR3_B:
- if (!kvm_cpu_cap_has(X86_FEATURE_INTEL_PT) ||
- msrs_to_save_all[i] - MSR_IA32_RTIT_ADDR0_A >=
- intel_pt_validate_hw_cap(PT_CAP_num_address_ranges) * 2)
- continue;
- break;
- case MSR_ARCH_PERFMON_PERFCTR0 ... MSR_ARCH_PERFMON_PERFCTR_MAX:
- if (msrs_to_save_all[i] - MSR_ARCH_PERFMON_PERFCTR0 >=
- min(KVM_INTEL_PMC_MAX_GENERIC, kvm_pmu_cap.num_counters_gp))
- continue;
- break;
- case MSR_ARCH_PERFMON_EVENTSEL0 ... MSR_ARCH_PERFMON_EVENTSEL_MAX:
- if (msrs_to_save_all[i] - MSR_ARCH_PERFMON_EVENTSEL0 >=
- min(KVM_INTEL_PMC_MAX_GENERIC, kvm_pmu_cap.num_counters_gp))
- continue;
- break;
- case MSR_ARCH_PERFMON_FIXED_CTR0 ... MSR_ARCH_PERFMON_FIXED_CTR_MAX:
- if (msrs_to_save_all[i] - MSR_ARCH_PERFMON_FIXED_CTR0 >=
- min(KVM_PMC_MAX_FIXED, kvm_pmu_cap.num_counters_fixed))
- continue;
- break;
- case MSR_IA32_XFD:
- case MSR_IA32_XFD_ERR:
- if (!kvm_cpu_cap_has(X86_FEATURE_XFD))
- continue;
- break;
- default:
- break;
- }
-
- msrs_to_save[num_msrs_to_save++] = msrs_to_save_all[i];
+ if (enable_pmu) {
+ for (i = 0; i < ARRAY_SIZE(msrs_to_save_pmu); i++)
+ kvm_probe_msr_to_save(msrs_to_save_pmu[i]);
}
for (i = 0; i < ARRAY_SIZE(emulated_msrs_all); i++) {
base-commit: 248deec419748c75f3a0fd6c075fc7687441b7ea
--
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