KVM: arm64: Expose PMMIR_EL1.SLOTS under strict PMUv3 UAPI

Introduce a new field pmmir_slots in struct kvm_arch to store
PMMIR_EL1.SLOTS. It only saves the actual hardware PMU value when
the VMM explicitly selects a PMU under KVM_ARM_VCPU_PMU_V3_STRICT.
Otherwise, it stays 0 after allocation.

Use this field to implement guest access, userspace get, and userspace
set for PMMIR_EL1:
- access_pmmir(): uses the value in kvm->arch.pmmir_slots directly. If
  the VMM selected a PMU and KVM_ARM_VCPU_PMU_V3_STRICT is set, the guest
  can correctly read the underlying core's SLOTS. Otherwise, it continues
  to read 0 since the true SLOTS value can be nondeterministic.
- get_pmmir(): same as access_pmmir().
- set_pmmir(): only the SLOTS field is writable; a value setting any
  other bit is rejected with -EINVAL, since get_pmmir() returns SLOTS
  zero-extended. A value of 0 resets kvm->arch.pmmir_slots to 0 for
  backward compatibility, as the register is RAZ in older KVM, a value
  matching the current SLOTS is accepted as a no-op, and anything else is
  rejected with -EINVAL. Once the VM has run PMMIR_EL1 is immutable, so a
  mismatching write then returns -EBUSY.

The register is now exposed via KVM_GET_REG_LIST for PMUv3 vCPUs, so add
it to the get-reg-list selftest's PMU register list.

Signed-off-by: Congkai Tan <congkai@amazon.com>
Reviewed-by: Geoff Blake <blakgeof@amazon.com>
Reviewed-by: Haris Okanovic <harisokn@amazon.com>
Reviewed-by: Stanislav Spassov <stanspas@amazon.de>
Co-developed-by: Oliver Upton <oupton@kernel.org>
Reviewed-by: Fuad Tabba <fuad.tabba@linux.dev>
Tested-by: Fuad Tabba <fuad.tabba@linux.dev>
Link: https://patch.msgid.link/20260722202702.4165917-2-congkai@amazon.com
Signed-off-by: Oliver Upton <oupton@kernel.org>

1 files changed, 4 insertions, 0 deletions

diff --git a/include/kvm/arm_pmu.h b/include/kvm/arm_pmu.h
index b5e5942204fc..6b4a118d17ca 100644
--- a/include/kvm/arm_pmu.h
+++ b/include/kvm/arm_pmu.h
@@ -75,6 +75,9 @@ void kvm_vcpu_pmu_resync_el0(void);
 #define kvm_vcpu_has_pmu(vcpu)					\
 	(vcpu_has_feature(vcpu, KVM_ARM_VCPU_PMU_V3))
 
+#define kvm_vcpu_has_pmuv3_strict(vcpu)				\
+	(vcpu_has_feature(vcpu, KVM_ARM_VCPU_PMU_V3_STRICT))
+
 /*
  * Updates the vcpu's view of the pmu events for this cpu.
  * Must be called before every vcpu run after disabling interrupts, to ensure
@@ -160,6 +163,7 @@ static inline u64 kvm_pmu_get_pmceid(struct kvm_vcpu *vcpu, bool pmceid1)
 }
 
 #define kvm_vcpu_has_pmu(vcpu)		({ false; })
+#define kvm_vcpu_has_pmuv3_strict(vcpu)	({ false; })
 static inline void kvm_pmu_update_vcpu_events(struct kvm_vcpu *vcpu) {}
 static inline void kvm_vcpu_pmu_restore_guest(struct kvm_vcpu *vcpu) {}
 static inline void kvm_vcpu_pmu_restore_host(struct kvm_vcpu *vcpu) {}