linux-kernel - [PATCH 1/2] KVM: selftests: Rework macros in PMU counters test to prep for multi-insn loop

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Date: Thu, 27 Jun 2024 17:55:56 -0700
From: Sean Christopherson <seanjc@...gle.com>
To: Sean Christopherson <seanjc@...gle.com>, Paolo Bonzini <pbonzini@...hat.com>
Cc: kvm@...r.kernel.org, linux-kernel@...r.kernel.org, 
	Maxim Levitsky <mlevitsk@...hat.com>
Subject: [PATCH 1/2] KVM: selftests: Rework macros in PMU counters test to
 prep for multi-insn loop

Tweak the macros in the PMU counters test to prepare for moving the
CLFLUSH+MFENCE instructions into the loop body, to fix an issue where
a single CLFUSH doesn't guarantee an LLC miss.

Signed-off-by: Sean Christopherson <seanjc@...gle.com>
---
 .../selftests/kvm/x86_64/pmu_counters_test.c  | 28 +++++++++++++------
 1 file changed, 19 insertions(+), 9 deletions(-)

diff --git a/tools/testing/selftests/kvm/x86_64/pmu_counters_test.c b/tools/testing/selftests/kvm/x86_64/pmu_counters_test.c
index 96446134c00b..bb40d7c0f83e 100644
--- a/tools/testing/selftests/kvm/x86_64/pmu_counters_test.c
+++ b/tools/testing/selftests/kvm/x86_64/pmu_counters_test.c
@@ -7,15 +7,25 @@
 #include "pmu.h"
 #include "processor.h"
 
-/* Number of LOOP instructions for the guest measurement payload. */
-#define NUM_BRANCHES		10
+/* Number of iterations of the loop for the guest measurement payload. */
+#define NUM_LOOPS			10
+
+/* Each iteration of the loop retires one branch instruction. */
+#define NUM_BRANCH_INSNS_RETIRED	(NUM_LOOPS)
+
+/* Number of instructions in each loop. */
+#define NUM_INSNS_PER_LOOP		1
+
 /*
  * Number of "extra" instructions that will be counted, i.e. the number of
- * instructions that are needed to set up the loop and then disabled the
+ * instructions that are needed to set up the loop and then disable the
  * counter.  1 CLFLUSH/CLFLUSHOPT/NOP, 1 MFENCE, 2 MOV, 2 XOR, 1 WRMSR.
  */
-#define NUM_EXTRA_INSNS		7
-#define NUM_INSNS_RETIRED	(NUM_BRANCHES + NUM_EXTRA_INSNS)
+#define NUM_EXTRA_INSNS			7
+
+/* Total number of instructions retired within the measured section. */
+#define NUM_INSNS_RETIRED		(NUM_LOOPS * NUM_INSNS_PER_LOOP + NUM_EXTRA_INSNS)
+
 
 static uint8_t kvm_pmu_version;
 static bool kvm_has_perf_caps;
@@ -100,7 +110,7 @@ static void guest_assert_event_count(uint8_t idx,
 		GUEST_ASSERT_EQ(count, NUM_INSNS_RETIRED);
 		break;
 	case INTEL_ARCH_BRANCHES_RETIRED_INDEX:
-		GUEST_ASSERT_EQ(count, NUM_BRANCHES);
+		GUEST_ASSERT_EQ(count, NUM_BRANCH_INSNS_RETIRED);
 		break;
 	case INTEL_ARCH_LLC_REFERENCES_INDEX:
 	case INTEL_ARCH_LLC_MISSES_INDEX:
@@ -120,7 +130,7 @@ static void guest_assert_event_count(uint8_t idx,
 	}
 
 sanity_checks:
-	__asm__ __volatile__("loop ." : "+c"((int){NUM_BRANCHES}));
+	__asm__ __volatile__("loop ." : "+c"((int){NUM_LOOPS}));
 	GUEST_ASSERT_EQ(_rdpmc(pmc), count);
 
 	wrmsr(pmc_msr, 0xdead);
@@ -147,7 +157,7 @@ do {										\
 	__asm__ __volatile__("wrmsr\n\t"					\
 			     clflush "\n\t"					\
 			     "mfence\n\t"					\
-			     "1: mov $" __stringify(NUM_BRANCHES) ", %%ecx\n\t"	\
+			     "1: mov $" __stringify(NUM_LOOPS) ", %%ecx\n\t"	\
 			     FEP "loop .\n\t"					\
 			     FEP "mov %%edi, %%ecx\n\t"				\
 			     FEP "xor %%eax, %%eax\n\t"				\
@@ -500,7 +510,7 @@ static void guest_test_fixed_counters(void)
 		wrmsr(MSR_CORE_PERF_FIXED_CTR0 + i, 0);
 		wrmsr(MSR_CORE_PERF_FIXED_CTR_CTRL, FIXED_PMC_CTRL(i, FIXED_PMC_KERNEL));
 		wrmsr(MSR_CORE_PERF_GLOBAL_CTRL, FIXED_PMC_GLOBAL_CTRL_ENABLE(i));
-		__asm__ __volatile__("loop ." : "+c"((int){NUM_BRANCHES}));
+		__asm__ __volatile__("loop ." : "+c"((int){NUM_LOOPS}));
 		wrmsr(MSR_CORE_PERF_GLOBAL_CTRL, 0);
 		val = rdmsr(MSR_CORE_PERF_FIXED_CTR0 + i);
 
-- 
2.45.2.803.g4e1b14247a-goog