KVM: arm64: Advertise PMUv3 if IMPDEF traps are present

Advertise a baseline PMUv3 implementation when running on hardware with
IMPDEF traps of the PMUv3 sysregs.

Tested-by: Janne Grunau <j@jannau.net>
Reviewed-by: Marc Zyngier <maz@kernel.org>
Link: https://lore.kernel.org/r/20250305202641.428114-11-oliver.upton@linux.dev
Signed-off-by: Oliver Upton <oliver.upton@linux.dev>

diff --git a/arch/arm64/kvm/pmu-emul.c b/arch/arm64/kvm/pmu-emul.c
index 0a2023aabe184bc53a2f1d05d29f4b496b8e3c82..38d9490c17fd9aa48d2df9f02b91d20bd1482790 100644 (file)
--- a/arch/arm64/kvm/pmu-emul.c
+++ b/arch/arm64/kvm/pmu-emul.c
@@ -1231,7 +1231,17 @@ u8 kvm_arm_pmu_get_pmuver_limit(void)
        pmuver = SYS_FIELD_GET(ID_AA64DFR0_EL1, PMUVer,
                               read_sanitised_ftr_reg(SYS_ID_AA64DFR0_EL1));
 
-       /* Treat IMPLEMENTATION DEFINED functionality as unimplemented */
+       /*
+        * Spoof a barebones PMUv3 implementation if the system supports IMPDEF
+        * traps of the PMUv3 sysregs
+        */
+       if (cpus_have_final_cap(ARM64_WORKAROUND_PMUV3_IMPDEF_TRAPS))
+               return ID_AA64DFR0_EL1_PMUVer_IMP;
+
+       /*
+        * Otherwise, treat IMPLEMENTATION DEFINED functionality as
+        * unimplemented
+        */
        if (pmuver == ID_AA64DFR0_EL1_PMUVer_IMP_DEF)
                return 0;