The number of PMU event counters is indicated in PMCR_EL0.N.
For a vCPU with PMUv3 configured, its value will be the same as
the host value by default. Userspace can set PMCR_EL0.N for the
vCPU to a lower value than the host value using KVM_SET_ONE_REG.
However, it is practically unsupported, as reset_pmcr() resets
PMCR_EL0.N to the host value on vCPU reset.
Change reset_pmcr() to preserve the vCPU's PMCR_EL0.N value on
vCPU reset so that userspace can limit the number of the PMU
event counter on the vCPU.
Signed-off-by: Reiji Watanabe <rei...@google.com>
---
arch/arm64/kvm/pmu-emul.c | 6 ++++++
arch/arm64/kvm/sys_regs.c | 4 +++-
2 files changed, 9 insertions(+), 1 deletion(-)
diff --git a/arch/arm64/kvm/pmu-emul.c b/arch/arm64/kvm/pmu-emul.c
index 24908400e190..937a272b00a5 100644
--- a/arch/arm64/kvm/pmu-emul.c
+++ b/arch/arm64/kvm/pmu-emul.c
@@ -213,6 +213,12 @@ void kvm_pmu_vcpu_init(struct kvm_vcpu *vcpu)
for (i = 0; i < ARMV8_PMU_MAX_COUNTERS; i++)
pmu->pmc[i].idx = i;
+
+ /*
+ * Initialize PMCR_EL0 for the vCPU with the host value so that
+ * the value is available at the very first vCPU reset.
+ */
+ __vcpu_sys_reg(vcpu, PMCR_EL0) = read_sysreg(pmcr_el0);
}
/**
diff --git a/arch/arm64/kvm/sys_regs.c b/arch/arm64/kvm/sys_regs.c
index 4959658b502c..67c1bd39b478 100644
--- a/arch/arm64/kvm/sys_regs.c
+++ b/arch/arm64/kvm/sys_regs.c
@@ -637,8 +637,10 @@ static void reset_pmcr(struct kvm_vcpu *vcpu, const struct
sys_reg_desc *r)
if (!kvm_arm_support_pmu_v3())
return;
+ /* PMCR_EL0 for the vCPU is set to the host value at vCPU creation. */
+
/* Only preserve PMCR_EL0.N, and reset the rest to 0 */
- pmcr = read_sysreg(pmcr_el0) & (ARMV8_PMU_PMCR_N_MASK <<
ARMV8_PMU_PMCR_N_SHIFT);
+ pmcr = __vcpu_sys_reg(vcpu, r->reg) & (ARMV8_PMU_PMCR_N_MASK <<
ARMV8_PMU_PMCR_N_SHIFT);
if (!kvm_supports_32bit_el0())
pmcr |= ARMV8_PMU_PMCR_LC;
--
2.39.0.314.g84b9a713c41-goog
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