If KVM has enabled LPA2 support then check that the RMM also supports
it. If there is a mismatch then disable support for realm guests as the
VMM may attempt to create a guest which is incompatible with the RMM.

Also check for SHA-256 support in the RMM as to begin with we only
support SHA-256 based measurements. This can be relaxed in the future.

Reviewed-by: Suzuki K Poulose <suzuki.poulose@arm.com>
Signed-off-by: Steven Price <steven.price@arm.com>
---
 arch/arm64/kvm/rmi.c | 25 +++++++++++++++++++++++++
 1 file changed, 25 insertions(+)

diff --git a/arch/arm64/kvm/rmi.c b/arch/arm64/kvm/rmi.c
index 9d118768550d..5b07beff8bc9 100644
--- a/arch/arm64/kvm/rmi.c
+++ b/arch/arm64/kvm/rmi.c
@@ -6,8 +6,30 @@
 #include <linux/arm-rmi-cmds.h>
 #include <linux/kvm_host.h>
 
+#include <asm/kvm_pgtable.h>
 #include <asm/virt.h>
 
+static bool rmi_has_feature(int reg, unsigned long feature)
+{
+	return !!u64_get_bits(rmi_feat_reg(reg), feature);
+}
+
+static int rmm_check_features(void)
+{
+	if (kvm_lpa2_is_enabled() &&
+	    !rmi_has_feature(0, RMI_FEATURE_REGISTER_0_LPA2)) {
+		kvm_err("RMM doesn't support LPA2\n");
+		return -ENXIO;
+	}
+
+	if (!rmi_has_feature(1, RMI_FEATURE_REGISTER_1_HASH_SHA_256)) {
+		kvm_err("RMM doesn't support SHA-256 measurements\n");
+		return -ENXIO;
+	}
+
+	return 0;
+}
+
 void kvm_init_rmi(void)
 {
 	if (kvm_get_mode() != KVM_MODE_RMM)
@@ -16,5 +38,8 @@ void kvm_init_rmi(void)
 	if (!is_rmi_available())
 		return;
 
+	if (rmm_check_features())
+		return;
+
 	/* Future patch will enable static branch kvm_rmi_is_available */
 }
-- 
2.43.0