KVM: arm64: pkvm: Report optional ID register traps with a 0x18 syndrome

With FEAT_IDST, unimplemented system registers in the feature ID space
must be reported using EC=0x18 at the closest handling EL, rather than
with an UNDEF.

Most of these system registers are always implemented thanks to their
dependency on FEAT_AA64, except for a set of (currently) three registers:
GMID_EL1 (depending on MTE2), CCSIDR2_EL1 (depending on FEAT_CCIDX),
and SMIDR_EL1 (depending on SME).

For these three registers, report their trap as EC=0x18 if they
end-up trapping into KVM and that FEAT_IDST is implemented in the guest.
Otherwise, just make them UNDEF.

Link: https://patch.msgid.link/20260108173233.2911955-9-maz@kernel.org
Signed-off-by: Marc Zyngier <maz@kernel.org>

diff --git a/arch/arm64/kvm/hyp/nvhe/sys_regs.c b/arch/arm64/kvm/hyp/nvhe/sys_regs.c
index b197f3eb272c1340c8a432b1d301e7d3faae2576..06d28621722eee561df31bc55ca1262a14a4b42a 100644 (file)
--- a/arch/arm64/kvm/hyp/nvhe/sys_regs.c
+++ b/arch/arm64/kvm/hyp/nvhe/sys_regs.c
@@ -347,6 +347,18 @@ static bool pvm_gic_read_sre(struct kvm_vcpu *vcpu,
        return true;
 }
 
+static bool pvm_idst_access(struct kvm_vcpu *vcpu,
+                           struct sys_reg_params *p,
+                           const struct sys_reg_desc *r)
+{
+       if (kvm_has_feat(vcpu->kvm, ID_AA64MMFR2_EL1, IDS, IMP))
+               inject_sync64(vcpu, kvm_vcpu_get_esr(vcpu));
+       else
+               inject_undef64(vcpu);
+
+       return false;
+}
+
 /* Mark the specified system register as an AArch32 feature id register. */
 #define AARCH32(REG) { SYS_DESC(REG), .access = pvm_access_id_aarch32 }
 
@@ -477,6 +489,9 @@ static const struct sys_reg_desc pvm_sys_reg_descs[] = {
 
        HOST_HANDLED(SYS_CCSIDR_EL1),
        HOST_HANDLED(SYS_CLIDR_EL1),
+       { SYS_DESC(SYS_CCSIDR2_EL1), .access = pvm_idst_access },
+       { SYS_DESC(SYS_GMID_EL1), .access = pvm_idst_access },
+       { SYS_DESC(SYS_SMIDR_EL1), .access = pvm_idst_access },
        HOST_HANDLED(SYS_AIDR_EL1),
        HOST_HANDLED(SYS_CSSELR_EL1),
        HOST_HANDLED(SYS_CTR_EL0),