KVM: x86/pmu: Allow programming events that match unsupported arch events

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, 0x01a4
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>
Reviewed-by: Kan Liang <kan.liang@linux.intel.com>
Tested-by: Dapeng Mi <dapeng1.mi@linux.intel.com>
Link: https://lore.kernel.org/r/20240109230250.424295-3-seanjc@google.com
Signed-off-by: Sean Christopherson <seanjc@google.com>

1 files changed, 0 insertions, 38 deletions

diff --git a/arch/x86/kvm/vmx/pmu_intel.c b/arch/x86/kvm/vmx/pmu_intel.c
index 8207f8c03585..1a7d021a6c7b 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);
@@ -780,7 +743,6 @@ 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,