[PATCH v2 4/5] KVM: arm64: Report optional ID register traps with a 0x18 syndrome

[Marc Zyngier]

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 not implemented in the
guest. Otherwise, just make them UNDEF.

Signed-off-by: Marc Zyngier <maz at kernel.org>
---
 arch/arm64/kvm/sys_regs.c | 16 +++++++++++++---
 1 file changed, 13 insertions(+), 3 deletions(-)

diff --git a/arch/arm64/kvm/sys_regs.c b/arch/arm64/kvm/sys_regs.c
index 2ca6862e935b5..7705f703e7c6d 100644
--- a/arch/arm64/kvm/sys_regs.c
+++ b/arch/arm64/kvm/sys_regs.c
@@ -82,6 +82,16 @@ static bool write_to_read_only(struct kvm_vcpu *vcpu,
 			"sys_reg write to read-only register");
 }
 
+static bool idst_access(struct kvm_vcpu *vcpu, struct sys_reg_params *p,
+			const struct sys_reg_desc *r)
+{
+	if (kvm_has_feat_enum(vcpu->kvm, ID_AA64MMFR2_EL1, IDS, 0x0))
+		return undef_access(vcpu, p, r);
+
+	kvm_inject_sync(vcpu, kvm_vcpu_get_esr(vcpu));
+	return false;
+}
+
 enum sr_loc_attr {
 	SR_LOC_MEMORY	= 0,	  /* Register definitely in memory */
 	SR_LOC_LOADED	= BIT(0), /* Register on CPU, unless it cannot */
@@ -3399,9 +3409,9 @@ static const struct sys_reg_desc sys_reg_descs[] = {
 	{ SYS_DESC(SYS_CCSIDR_EL1), access_ccsidr },
 	{ SYS_DESC(SYS_CLIDR_EL1), access_clidr, reset_clidr, CLIDR_EL1,
 	  .set_user = set_clidr, .val = ~CLIDR_EL1_RES0 },
-	{ SYS_DESC(SYS_CCSIDR2_EL1), undef_access },
-	{ SYS_DESC(SYS_GMID_EL1), undef_access },
-	{ SYS_DESC(SYS_SMIDR_EL1), undef_access },
+	{ SYS_DESC(SYS_CCSIDR2_EL1), idst_access },
+	{ SYS_DESC(SYS_GMID_EL1), idst_access },
+	{ SYS_DESC(SYS_SMIDR_EL1), idst_access },
 	IMPLEMENTATION_ID(AIDR_EL1, GENMASK_ULL(63, 0)),
 	{ SYS_DESC(SYS_CSSELR_EL1), access_csselr, reset_unknown, CSSELR_EL1 },
 	ID_FILTERED(CTR_EL0, ctr_el0,
-- 
2.47.3