From bbef6317f97b8612a694ddc2ff6e7ca81780768d Mon Sep 17 00:00:00 2001 From: Oliver Upton Date: Wed, 22 Jul 2026 20:27:01 +0000 Subject: [PATCH] KVM: arm64: Ignore writes to PMCR_EL0.N when using strict UAPI KVM allows userspace to configure the number of event counters by writing to PMCR_EL0.N. While this makes a bit of sense prior to NV, the value of the field is context-dependent whether or not the vCPU is at EL2 or EL1. As such, the vCPU attribute was added afterwards and made mandatory for NV. As we're in the process of papering over old mistakes, force userspace to use the vCPU attribute if KVM_ARM_VCPU_PMU_V3_STRICT is set. Reviewed-by: Geoff Blake Reviewed-by: Haris Okanovic Signed-off-by: Congkai Tan Reviewed-by: Fuad Tabba Tested-by: Fuad Tabba Link: https://patch.msgid.link/20260722202702.4165917-4-congkai@amazon.com Signed-off-by: Oliver Upton --- arch/arm64/kvm/sys_regs.c | 1 + 1 file changed, 1 insertion(+) diff --git a/arch/arm64/kvm/sys_regs.c b/arch/arm64/kvm/sys_regs.c index 4c6f608c4fe5..e93f11b90813 100644 --- a/arch/arm64/kvm/sys_regs.c +++ b/arch/arm64/kvm/sys_regs.c @@ -1502,6 +1502,7 @@ static int set_pmcr(struct kvm_vcpu *vcpu, const struct sys_reg_desc *r, */ if (!kvm_vm_has_ran_once(kvm) && !vcpu_has_nv(vcpu) && + !kvm_vcpu_has_pmuv3_strict(vcpu) && new_n <= kvm_arm_pmu_get_max_counters(kvm)) kvm->arch.nr_pmu_counters = new_n;