Re: [PATCH v8 26/26] KVM: selftests: Extend PMU counters test to validate RDPMC after WRMSR

[Sean Christopherson <seanjc@google.com>]

On Mon, Nov 13, 2023, Jinrong Liang wrote:
> 在 2023/11/10 10:13, Sean Christopherson 写道:
> > Extend the read/write PMU counters subtest to verify that RDPMC also reads
> > back the written value.  Opportunsitically verify that attempting to use
> > the "fast" mode of RDPMC fails, as the "fast" flag is only supported by
> > non-architectural PMUs, which KVM doesn't virtualize.
> > 
> > Signed-off-by: Sean Christopherson <seanjc@google.com>
> > ---
> > +		/* Redo the read tests with RDPMC, and with forced emulation. */
> > +		vector = rdpmc_safe(rdpmc_idx, &val);
> > +		GUEST_ASSERT_PMC_MSR_ACCESS(RDPMC, rdpmc_idx, !expect_success, vector);
> > +		if (expect_success)
> > +			GUEST_ASSERT_PMC_VALUE(RDPMC, rdpmc_idx, val, expected_val);
> > +
> > +		vector = rdpmc_safe_fep(rdpmc_idx, &val);
> > +		GUEST_ASSERT_PMC_MSR_ACCESS(RDPMC, rdpmc_idx, !expect_success, vector);
> > +		if (expect_success)
> > +			GUEST_ASSERT_PMC_VALUE(RDPMC, rdpmc_idx, val, expected_val);

> This test case failed on my Intel machine.
> 
> Error message：
> Testing arch events, PMU version 0, perf_caps = 0
> Testing GP counters, PMU version 0, perf_caps = 0
> ==== Test Assertion Failure ====
>   lib/x86_64/processor.c:1100: Unhandled exception in guest
>   pid=464480 tid=464480 errno=4 - Interrupted system call
>      1	0x00000000004120e1: assert_on_unhandled_exception 于 processor.c:1146
>      2	0x00000000004062d9: _vcpu_run 于 kvm_util.c:1634
>      3	0x00000000004062fa: vcpu_run 于 kvm_util.c:1645
>      4	0x0000000000403697: run_vcpu 于 pmu_counters_test.c:56
>      5	0x00000000004026fc: test_gp_counters 于 pmu_counters_test.c:434
>      6	(已内连入)test_intel_counters 于 pmu_counters_test.c:580
>      7	(已内连入)main 于 pmu_counters_test.c:604
>      8	0x00007f7a2f03ad84: ?? ??:0
>      9	0x00000000004028bd: _start 于 ??:?
>   Unhandled exception '0x6' at guest RIP '0x402bab'

Argh, I didn't add a check to see if forced emulation is actually enabled (forced
emulation uses a magic "prefix" to trigger a #UD, which KVM intercepts; if forced
emulation isn't enabled, KVM ignores the magic prefix and reflects the #UD back
into the guest).

This fixes the test for me:

---
 .../selftests/kvm/x86_64/pmu_counters_test.c  | 42 ++++++++++++-------
 1 file changed, 26 insertions(+), 16 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 248ebe8c0577..ae5f6042f1e8 100644
--- a/tools/testing/selftests/kvm/x86_64/pmu_counters_test.c
+++ b/tools/testing/selftests/kvm/x86_64/pmu_counters_test.c
@@ -325,6 +325,26 @@ __GUEST_ASSERT(expect_gp ? vector == GP_VECTOR : !vector,			\
 		       "Expected " #insn "(0x%x) to yield 0x%lx, got 0x%lx",	\
 		       msr, expected_val, val);
 
+static void guest_test_rdpmc(uint32_t rdpmc_idx, bool expect_success,
+			     uint64_t expected_val)
+{
+	uint8_t vector;
+	uint64_t val;
+
+	vector = rdpmc_safe(rdpmc_idx, &val);
+	GUEST_ASSERT_PMC_MSR_ACCESS(RDPMC, rdpmc_idx, !expect_success, vector);
+	if (expect_success)
+		GUEST_ASSERT_PMC_VALUE(RDPMC, rdpmc_idx, val, expected_val);
+
+	if (!is_forced_emulation_enabled)
+		return;
+
+	vector = rdpmc_safe_fep(rdpmc_idx, &val);
+	GUEST_ASSERT_PMC_MSR_ACCESS(RDPMC, rdpmc_idx, !expect_success, vector);
+	if (expect_success)
+		GUEST_ASSERT_PMC_VALUE(RDPMC, rdpmc_idx, val, expected_val);
+}
+
 static void guest_rd_wr_counters(uint32_t base_msr, uint8_t nr_possible_counters,
 				 uint8_t nr_counters, uint32_t or_mask)
 {
@@ -367,20 +387,15 @@ static void guest_rd_wr_counters(uint32_t base_msr, uint8_t nr_possible_counters
 		if (!expect_gp)
 			GUEST_ASSERT_PMC_VALUE(RDMSR, msr, val, expected_val);
 
+		/*
+		 * Redo the read tests with RDPMC, which has different indexing
+		 * semantics and additional capabilities.
+		 */
 		rdpmc_idx = i;
 		if (base_msr == MSR_CORE_PERF_FIXED_CTR0)
 			rdpmc_idx |= INTEL_RDPMC_FIXED;
 
-		/* Redo the read tests with RDPMC, and with forced emulation. */
-		vector = rdpmc_safe(rdpmc_idx, &val);
-		GUEST_ASSERT_PMC_MSR_ACCESS(RDPMC, rdpmc_idx, !expect_success, vector);
-		if (expect_success)
-			GUEST_ASSERT_PMC_VALUE(RDPMC, rdpmc_idx, val, expected_val);
-
-		vector = rdpmc_safe_fep(rdpmc_idx, &val);
-		GUEST_ASSERT_PMC_MSR_ACCESS(RDPMC, rdpmc_idx, !expect_success, vector);
-		if (expect_success)
-			GUEST_ASSERT_PMC_VALUE(RDPMC, rdpmc_idx, val, expected_val);
+		guest_test_rdpmc(rdpmc_idx, expect_success, expected_val);
 
 		/*
 		 * KVM doesn't support non-architectural PMUs, i.e. it should
@@ -389,12 +404,7 @@ static void guest_rd_wr_counters(uint32_t base_msr, uint8_t nr_possible_counters
 		 */
 		GUEST_ASSERT(!expect_success || !pmu_has_fast_mode);
 		rdpmc_idx |= INTEL_RDPMC_FAST;
-
-		vector = rdpmc_safe(rdpmc_idx, &val);
-		GUEST_ASSERT_PMC_MSR_ACCESS(RDPMC, rdpmc_idx, true, vector);
-
-		vector = rdpmc_safe_fep(rdpmc_idx, &val);
-		GUEST_ASSERT_PMC_MSR_ACCESS(RDPMC, rdpmc_idx, true, vector);
+		guest_test_rdpmc(rdpmc_idx, false, -1ull);
 
 		vector = wrmsr_safe(msr, 0);
 		GUEST_ASSERT_PMC_MSR_ACCESS(WRMSR, msr, expect_gp, vector);

base-commit: 743a1a6d106931691be32e081e929d9b3de5777f
--