[RFC PATCH v2 4/4] KVM: arm64: Make guests see only counters they can access

[Colton Lewis]

The ARM architecture specifies that when MDCR_EL2.HPMN is set, EL1 and
EL0, which includes KVM guests, should read that value for PMCR.N.

Signed-off-by: Colton Lewis <coltonle...@google.com>
---
 arch/arm64/kvm/debug.c                                  | 3 +--
 arch/arm64/kvm/pmu-emul.c                               | 8 +++++++-
 tools/testing/selftests/kvm/arm64/vpmu_counter_access.c | 2 +-
 3 files changed, 9 insertions(+), 4 deletions(-)

diff --git a/arch/arm64/kvm/debug.c b/arch/arm64/kvm/debug.c
index 0e4c805e7e89..7c04db00bf6c 100644
--- a/arch/arm64/kvm/debug.c
+++ b/arch/arm64/kvm/debug.c
@@ -36,8 +36,7 @@ static void kvm_arm_setup_mdcr_el2(struct kvm_vcpu *vcpu)
         * This also clears MDCR_EL2_E2PB_MASK and MDCR_EL2_E2TB_MASK
         * to disable guest access to the profiling and trace buffers
         */
-       vcpu->arch.mdcr_el2 = FIELD_PREP(MDCR_EL2_HPMN,
-                                        *host_data_ptr(nr_event_counters));
+       vcpu->arch.mdcr_el2 = FIELD_PREP(MDCR_EL2_HPMN, read_mdcr());
        vcpu->arch.mdcr_el2 |= (MDCR_EL2_TPM |
                                MDCR_EL2_TPMS |
                                MDCR_EL2_TTRF |
diff --git a/arch/arm64/kvm/pmu-emul.c b/arch/arm64/kvm/pmu-emul.c
index 6c5950b9ceac..052ce8c721fe 100644
--- a/arch/arm64/kvm/pmu-emul.c
+++ b/arch/arm64/kvm/pmu-emul.c
@@ -993,12 +993,18 @@ static bool pmu_irq_is_valid(struct kvm *kvm, int irq)
 u8 kvm_arm_pmu_get_max_counters(struct kvm *kvm)
 {
        struct arm_pmu *arm_pmu = kvm->arch.arm_pmu;
+       u8 limit;
+
+       if (arm_pmu->partitioned)
+               limit = arm_pmu->hpmn - 1;
+       else
+               limit = ARMV8_PMU_MAX_GENERAL_COUNTERS;
 
        /*
         * The arm_pmu->cntr_mask considers the fixed counter(s) as well.
         * Ignore those and return only the general-purpose counters.
         */
-       return bitmap_weight(arm_pmu->cntr_mask, 
ARMV8_PMU_MAX_GENERAL_COUNTERS);
+       return bitmap_weight(arm_pmu->cntr_mask, limit);
 }
 
 static void kvm_arm_set_pmu(struct kvm *kvm, struct arm_pmu *arm_pmu)
diff --git a/tools/testing/selftests/kvm/arm64/vpmu_counter_access.c 
b/tools/testing/selftests/kvm/arm64/vpmu_counter_access.c
index f16b3b27e32e..b5bc18b7528d 100644
--- a/tools/testing/selftests/kvm/arm64/vpmu_counter_access.c
+++ b/tools/testing/selftests/kvm/arm64/vpmu_counter_access.c
@@ -609,7 +609,7 @@ static void run_pmregs_validity_test(uint64_t pmcr_n)
  */
 static void run_error_test(uint64_t pmcr_n)
 {
-       pr_debug("Error test with pmcr_n %lu (larger than the host)\n", pmcr_n);
+       pr_debug("Error test with pmcr_n %lu (larger than the host allows)\n", 
pmcr_n);
 
        test_create_vpmu_vm_with_pmcr_n(pmcr_n, true);
        destroy_vpmu_vm();
-- 
2.48.1.502.g6dc24dfdaf-goog