[PATCH v7 02/19] KVM: x86/pmu: Allow programming events that match unsupported arch events

Sean Christopherson
2023-11-08T00:31:45Z

Remove KVM's bogus restriction that the guest can't program an event whose
encoding matches an unsupported architectural event. The enumeration of
an architectural event only says that if a CPU supports an architectural
event, then the event can be programmed using the architectural encoding.
The enumeration does NOT say anything about the encoding when the CPU
doesn't report support the architectural event.

Preventing the guest from counting events whose encoding happens to match
an architectural event breaks existing functionality whenever Intel adds
an architectural encoding that was *ever* used for a CPU that doesn't
enumerate support for the architectural event, even if the encoding is for
the exact same event!

E.g. the architectural encoding for Top-Down Slots is 0x01a4. Broadwell
CPUs, which do not support the Top-Down Slots architectural event, 0x10a4
is a valid, model-specific event. Denying guest usage of 0x01a4 if/when
KVM adds support for Top-Down slots would break any Broadwell-based guest.

Reported-by: Kan Liang <kan.liang@linux.intel.com>
Closes: https://lore.kernel.org/all/2004baa6-b494-462c-a11f-8104ea152c6a@linux.intel.com
Fixes: a21864486f7e ("KVM: x86/pmu: Fix available_event_types check for REF_CPU_CYCLES event")
Reviewed-by: Dapeng Mi <dapeng1.mi@linux.intel.com>
Reviewed-by: Jim Mattson <jmattson@google.com>
Signed-off-by: Sean Christopherson <seanjc@google.com>
---
arch/x86/include/asm/kvm-x86-pmu-ops.h | 1 -
arch/x86/kvm/pmu.c | 1 -
arch/x86/kvm/pmu.h | 1 -
arch/x86/kvm/svm/pmu.c | 6 ----
arch/x86/kvm/vmx/pmu_intel.c | 38 --------------------------
5 files changed, 47 deletions(-)

diff --git a/arch/x86/include/asm/kvm-x86-pmu-ops.h b/arch/x86/include/asm/kvm-x86-pmu-ops.h
index 6c98f4bb4228..884af8ef7657 100644
--- a/arch/x86/include/asm/kvm-x86-pmu-ops.h
+++ b/arch/x86/include/asm/kvm-x86-pmu-ops.h
@@ -12,7 +12,6 @@ BUILD_BUG_ON(1)
* a NULL definition, for example if "static_call_cond()" will be used
* at the call sites.
*/
-KVM_X86_PMU_OP(hw_event_available)
KVM_X86_PMU_OP(pmc_idx_to_pmc)
KVM_X86_PMU_OP(rdpmc_ecx_to_pmc)
KVM_X86_PMU_OP(msr_idx_to_pmc)
diff --git a/arch/x86/kvm/pmu.c b/arch/x86/kvm/pmu.c
index 9ae07db6f0f6..99ed72966528 100644
--- a/arch/x86/kvm/pmu.c
+++ b/arch/x86/kvm/pmu.c
@@ -374,7 +374,6 @@ static bool check_pmu_event_filter(struct kvm_pmc *pmc)
static bool pmc_event_is_allowed(struct kvm_pmc *pmc)
{
return pmc_is_globally_enabled(pmc) && pmc_speculative_in_use(pmc) &&
- static_call(kvm_x86_pmu_hw_event_available)(pmc) &&
check_pmu_event_filter(pmc);
}

diff --git a/arch/x86/kvm/pmu.h b/arch/x86/kvm/pmu.h
index 1d64113de488..10fe5bf02705 100644
--- a/arch/x86/kvm/pmu.h
+++ b/arch/x86/kvm/pmu.h
@@ -19,7 +19,6 @@
#define VMWARE_BACKDOOR_PMC_APPARENT_TIME 0x10002

struct kvm_pmu_ops {
- bool (*hw_event_available)(struct kvm_pmc *pmc);
struct kvm_pmc *(*pmc_idx_to_pmc)(struct kvm_pmu *pmu, int pmc_idx);
struct kvm_pmc *(*rdpmc_ecx_to_pmc)(struct kvm_vcpu *vcpu,
unsigned int idx, u64 *mask);
diff --git a/arch/x86/kvm/svm/pmu.c b/arch/x86/kvm/svm/pmu.c
index 373ff6a6687b..5596fe816ea8 100644
--- a/arch/x86/kvm/svm/pmu.c
+++ b/arch/x86/kvm/svm/pmu.c
@@ -73,11 +73,6 @@ static inline struct kvm_pmc *get_gp_pmc_amd(struct kvm_pmu *pmu, u32 msr,
return amd_pmc_idx_to_pmc(pmu, idx);
}

-static bool amd_hw_event_available(struct kvm_pmc *pmc)
-{
- return true;
-}
-
static bool amd_is_valid_rdpmc_ecx(struct kvm_vcpu *vcpu, unsigned int idx)
{
struct kvm_pmu *pmu = vcpu_to_pmu(vcpu);
@@ -249,7 +244,6 @@ static void amd_pmu_reset(struct kvm_vcpu *vcpu)
}

struct kvm_pmu_ops amd_pmu_ops __initdata = {
- .hw_event_available = amd_hw_event_available,
.pmc_idx_to_pmc = amd_pmc_idx_to_pmc,
.rdpmc_ecx_to_pmc = amd_rdpmc_ecx_to_pmc,
.msr_idx_to_pmc = amd_msr_idx_to_pmc,
diff --git a/arch/x86/kvm/vmx/pmu_intel.c b/arch/x86/kvm/vmx/pmu_intel.c
index c6e227edcf8e..7737ee2fc62f 100644
--- a/arch/x86/kvm/vmx/pmu_intel.c
+++ b/arch/x86/kvm/vmx/pmu_intel.c
@@ -101,43 +101,6 @@ static struct kvm_pmc *intel_pmc_idx_to_pmc(struct kvm_pmu *pmu, int pmc_idx)
}
}

-static bool intel_hw_event_available(struct kvm_pmc *pmc)
-{
- struct kvm_pmu *pmu = pmc_to_pmu(pmc);
- u8 event_select = pmc->eventsel & ARCH_PERFMON_EVENTSEL_EVENT;
- u8 unit_mask = (pmc->eventsel & ARCH_PERFMON_EVENTSEL_UMASK) >> 8;
- int i;
-
- /*
- * Fixed counters are always available if KVM reaches this point. If a
- * fixed counter is unsupported in hardware or guest CPUID, KVM doesn't
- * allow the counter's corresponding MSR to be written. KVM does use
- * architectural events to program fixed counters, as the interface to
- * perf doesn't allow requesting a specific fixed counter, e.g. perf
- * may (sadly) back a guest fixed PMC with a general purposed counter.
- * But if _hardware_ doesn't support the associated event, KVM simply
- * doesn't enumerate support for the fixed counter.
- */
- if (pmc_is_fixed(pmc))
- return true;
-
- BUILD_BUG_ON(ARRAY_SIZE(intel_arch_events) != NR_INTEL_ARCH_EVENTS);
-
- /*
- * Disallow events reported as unavailable in guest CPUID. Note, this
- * doesn't apply to pseudo-architectural events (see above).
- */
- for (i = 0; i < NR_REAL_INTEL_ARCH_EVENTS; i++) {
- if (intel_arch_events[i].eventsel != event_select ||
- intel_arch_events[i].unit_mask != unit_mask)
- continue;
-
- return pmu->available_event_types & BIT(i);
- }
-
- return true;
-}
-
static bool intel_is_valid_rdpmc_ecx(struct kvm_vcpu *vcpu, unsigned int idx)
{
struct kvm_pmu *pmu = vcpu_to_pmu(vcpu);
@@ -802,7 +765,6 @@ void intel_pmu_cross_mapped_check(struct kvm_pmu *pmu)
}

struct kvm_pmu_ops intel_pmu_ops __initdata = {
- .hw_event_available = intel_hw_event_available,
.pmc_idx_to_pmc = intel_pmc_idx_to_pmc,
.rdpmc_ecx_to_pmc = intel_rdpmc_ecx_to_pmc,
.msr_idx_to_pmc = intel_msr_idx_to_pmc,
--
2.42.0.869.gea05f2083d-goog