[PATCH 10/13] KVM: arm64: selftests: Use the vCPU attr for setting nr of PMU counters

Oliver Upton
2025-09-17T21:22:04Z

Configuring the number of implemented counters via PMCR_EL0.N was a bad
idea in retrospect as it interacts poorly with nested. Migrate the
selftest to use the vCPU attribute instead of the KVM_SET_ONE_REG
mechanism.

Signed-off-by: Oliver Upton <oliver.upton@linux.dev>
---
.../selftests/kvm/arm64/vpmu_counter_access.c | 59 +++++++++----------
1 file changed, 28 insertions(+), 31 deletions(-)

diff --git a/tools/testing/selftests/kvm/arm64/vpmu_counter_access.c b/tools/testing/selftests/kvm/arm64/vpmu_counter_access.c
index 2a8f31c8e59f..ae36325c022f 100644
--- a/tools/testing/selftests/kvm/arm64/vpmu_counter_access.c
+++ b/tools/testing/selftests/kvm/arm64/vpmu_counter_access.c
@@ -44,11 +44,6 @@ static uint64_t get_pmcr_n(uint64_t pmcr)
return FIELD_GET(ARMV8_PMU_PMCR_N, pmcr);
}

-static void set_pmcr_n(uint64_t *pmcr, uint64_t pmcr_n)
-{
- u64p_replace_bits((__u64 *) pmcr, pmcr_n, ARMV8_PMU_PMCR_N);
-}
-
static uint64_t get_counters_mask(uint64_t n)
{
uint64_t mask = BIT(ARMV8_PMU_CYCLE_IDX);
@@ -414,10 +409,6 @@ static void create_vpmu_vm(void *guest_code)
.attr = KVM_ARM_VCPU_PMU_V3_IRQ,
.addr = (uint64_t)&irq,
};
- struct kvm_device_attr init_attr = {
- .group = KVM_ARM_VCPU_PMU_V3_CTRL,
- .attr = KVM_ARM_VCPU_PMU_V3_INIT,
- };

/* The test creates the vpmu_vm multiple times. Ensure a clean state */
memset(&vpmu_vm, 0, sizeof(vpmu_vm));
@@ -444,9 +435,7 @@ static void create_vpmu_vm(void *guest_code)
pmuver >= ID_AA64DFR0_EL1_PMUVer_IMP,
"Unexpected PMUVER (0x%x) on the vCPU with PMUv3", pmuver);

- /* Initialize vPMU */
vcpu_ioctl(vpmu_vm.vcpu, KVM_SET_DEVICE_ATTR, &irq_attr);
- vcpu_ioctl(vpmu_vm.vcpu, KVM_SET_DEVICE_ATTR, &init_attr);
}

static void destroy_vpmu_vm(void)
@@ -472,33 +461,28 @@ static void run_vcpu(struct kvm_vcpu *vcpu, uint64_t pmcr_n)
}
}

-static void test_create_vpmu_vm_with_pmcr_n(uint64_t pmcr_n, bool expect_fail)
+static void test_create_vpmu_vm_with_nr_counters(unsigned int nr_counters, bool expect_fail)
{
struct kvm_vcpu *vcpu;
- uint64_t pmcr, pmcr_orig;
+ unsigned int prev;
+ int ret;

create_vpmu_vm(guest_code);
vcpu = vpmu_vm.vcpu;

- pmcr_orig = vcpu_get_reg(vcpu, KVM_ARM64_SYS_REG(SYS_PMCR_EL0));
- pmcr = pmcr_orig;
+ prev = get_pmcr_n(vcpu_get_reg(vcpu, KVM_ARM64_SYS_REG(SYS_PMCR_EL0)));

- /*
- * Setting a larger value of PMCR.N should not modify the field, and
- * return a success.
- */
- set_pmcr_n(&pmcr, pmcr_n);
- vcpu_set_reg(vcpu, KVM_ARM64_SYS_REG(SYS_PMCR_EL0), pmcr);
- pmcr = vcpu_get_reg(vcpu, KVM_ARM64_SYS_REG(SYS_PMCR_EL0));
+ ret = __vcpu_device_attr_set(vcpu, KVM_ARM_VCPU_PMU_V3_CTRL,
+ KVM_ARM_VCPU_PMU_V3_SET_NR_COUNTERS, &nr_counters);

if (expect_fail)
- TEST_ASSERT(pmcr_orig == pmcr,
- "PMCR.N modified by KVM to a larger value (PMCR: 0x%lx) for pmcr_n: 0x%lx",
- pmcr, pmcr_n);
+ TEST_ASSERT(ret && errno == EINVAL,
+ "Setting more PMU counters (%u) than available (%u) unexpectedly succeeded",
+ nr_counters, prev);
else
- TEST_ASSERT(pmcr_n == get_pmcr_n(pmcr),
- "Failed to update PMCR.N to %lu (received: %lu)",
- pmcr_n, get_pmcr_n(pmcr));
+ TEST_ASSERT(!ret, KVM_IOCTL_ERROR(KVM_SET_DEVICE_ATTR, ret));
+
+ vcpu_device_attr_set(vcpu, KVM_ARM_VCPU_PMU_V3_CTRL, KVM_ARM_VCPU_PMU_V3_INIT, NULL);
}

/*
@@ -513,7 +497,7 @@ static void run_access_test(uint64_t pmcr_n)

pr_debug("Test with pmcr_n %lu\n", pmcr_n);

- test_create_vpmu_vm_with_pmcr_n(pmcr_n, false);
+ test_create_vpmu_vm_with_nr_counters(pmcr_n, false);
vcpu = vpmu_vm.vcpu;

/* Save the initial sp to restore them later to run the guest again */
@@ -554,7 +538,7 @@ static void run_pmregs_validity_test(uint64_t pmcr_n)
uint64_t set_reg_id, clr_reg_id, reg_val;
uint64_t valid_counters_mask, max_counters_mask;

- test_create_vpmu_vm_with_pmcr_n(pmcr_n, false);
+ test_create_vpmu_vm_with_nr_counters(pmcr_n, false);
vcpu = vpmu_vm.vcpu;

valid_counters_mask = get_counters_mask(pmcr_n);
@@ -608,7 +592,7 @@ static void run_error_test(uint64_t pmcr_n)
{
pr_debug("Error test with pmcr_n %lu (larger than the host)\n", pmcr_n);

- test_create_vpmu_vm_with_pmcr_n(pmcr_n, true);
+ test_create_vpmu_vm_with_nr_counters(pmcr_n, true);
destroy_vpmu_vm();
}

@@ -626,12 +610,25 @@ static uint64_t get_pmcr_n_limit(void)
return get_pmcr_n(pmcr);
}

+static bool kvm_supports_nr_counters_attr(void)
+{
+ bool supported;
+
+ create_vpmu_vm(NULL);
+ supported = !__vcpu_has_device_attr(vpmu_vm.vcpu, KVM_ARM_VCPU_PMU_V3_CTRL,
+ KVM_ARM_VCPU_PMU_V3_SET_NR_COUNTERS);
+ destroy_vpmu_vm();
+
+ return supported;
+}
+
int main(void)
{
uint64_t i, pmcr_n;

TEST_REQUIRE(kvm_has_cap(KVM_CAP_ARM_PMU_V3));
TEST_REQUIRE(kvm_supports_vgic_v3());
+ TEST_REQUIRE(kvm_supports_nr_counters_attr());

pmcr_n = get_pmcr_n_limit();
for (i = 0; i <= pmcr_n; i++) {
--
2.47.3