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KVM: arm64: Fix MDCR_EL2.HPMN reset value

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The MDCR_EL2 documentation indicates that the HPMN field has
the following behaviour:

"On a Warm reset, this field resets to the expression NUM_PMU_COUNTERS."

However, it appears we reset it to zero, which is not very useful.

Add a reset helper for MDCR_EL2, and handle the case where userspace
changes the target PMU, which may force us to change HPMN again.

Reported-by: Joey Gouly <joey.gouly@arm.com>
Reviewed-by: Oliver Upton <oliver.upton@linux.dev>
Signed-off-by: Marc Zyngier <maz@kernel.org>
This commit is contained in:
Marc Zyngier
2025-02-17 10:17:20 +00:00
parent f12b54d7c2
commit c8823e51b5
2 changed files with 26 additions and 2 deletions
Download Patch File Download Diff File Expand all files Collapse all files
arch/arm64/kvm/pmu-emul.c
+19 -1
View File
@@ -1027,12 +1027,30 @@ u8 kvm_arm_pmu_get_max_counters(struct kvm *kvm)
return bitmap_weight(arm_pmu->cntr_mask, ARMV8_PMU_MAX_GENERAL_COUNTERS);
}
static void kvm_arm_set_nr_counters(struct kvm *kvm, unsigned int nr)
{
kvm->arch.nr_pmu_counters = nr;
/* Reset MDCR_EL2.HPMN behind the vcpus' back... */
if (test_bit(KVM_ARM_VCPU_HAS_EL2, kvm->arch.vcpu_features)) {
struct kvm_vcpu *vcpu;
unsigned long i;
kvm_for_each_vcpu(i, vcpu, kvm) {
u64 val = __vcpu_sys_reg(vcpu, MDCR_EL2);
val &= ~MDCR_EL2_HPMN;
val |= FIELD_PREP(MDCR_EL2_HPMN, kvm->arch.nr_pmu_counters);
__vcpu_sys_reg(vcpu, MDCR_EL2) = val;
}
}
}
static void kvm_arm_set_pmu(struct kvm *kvm, struct arm_pmu *arm_pmu)
{
lockdep_assert_held(&kvm->arch.config_lock);
kvm->arch.arm_pmu = arm_pmu;
kvm->arch.nr_pmu_counters = kvm_arm_pmu_get_max_counters(kvm);
kvm_arm_set_nr_counters(kvm, kvm_arm_pmu_get_max_counters(kvm));
}
/**
arch/arm64/kvm/sys_regs.c
+7 -1
View File
@@ -2698,6 +2698,12 @@ static int set_imp_id_reg(struct kvm_vcpu *vcpu, const struct sys_reg_desc *r,
.set_user = set_imp_id_reg, \
.reset = reset_imp_id_reg, \
.val = mask, \
}
static u64 reset_mdcr(struct kvm_vcpu *vcpu, const struct sys_reg_desc *r)
{
__vcpu_sys_reg(vcpu, r->reg) = vcpu->kvm->arch.nr_pmu_counters;
return vcpu->kvm->arch.nr_pmu_counters;
}
/*
@@ -3243,7 +3249,7 @@ static const struct sys_reg_desc sys_reg_descs[] = {
EL2_REG(SCTLR_EL2, access_rw, reset_val, SCTLR_EL2_RES1),
EL2_REG(ACTLR_EL2, access_rw, reset_val, 0),
EL2_REG_VNCR(HCR_EL2, reset_hcr, 0),
EL2_REG(MDCR_EL2, access_mdcr, reset_val, 0),
EL2_REG(MDCR_EL2, access_mdcr, reset_mdcr, 0),
EL2_REG(CPTR_EL2, access_rw, reset_val, CPTR_NVHE_EL2_RES1),
EL2_REG_VNCR(HSTR_EL2, reset_val, 0),
EL2_REG_VNCR(HFGRTR_EL2, reset_val, 0),