Re: [PATCH] arm64/mm: Fix __enable_mmu() for new TGRAN range values

On Fri, 05 Mar 2021 14:36:09 +0000,
Anshuman Khandual [off-list ref] wrote:

quoted

-	switch (cpuid_feature_extract_unsigned_field(mmfr0, tgran_2)) {
-	default:
-	case 1:
+	tgran_2 = cpuid_feature_extract_unsigned_field(mmfr0, tgran_2_shift);
+	if (tgran_2 == ID_AA64MMFR0_TGRAN_2_SUPPORTED_NONE) {
 		kvm_err("PAGE_SIZE not supported at Stage-2, giving up\n");
 		return -EINVAL;
-	case 0:
+	} else if (tgran_2 == ID_AA64MMFR0_TGRAN_2_SUPPORTED_DEFAULT) {
 		kvm_debug("PAGE_SIZE supported at Stage-2 (default)\n");
-		break;
-	case 2:
+	} else if (tgran_2 >= ID_AA64MMFR0_TGRAN_2_SUPPORTED_MIN &&
+		   tgran_2 <= ID_AA64MMFR0_TGRAN_2_SUPPORTED_MAX) {
 		kvm_debug("PAGE_SIZE supported at Stage-2 (advertised)\n");
-		break;
+	} else {
+		kvm_err("Unsupported value, giving up\n");
+		return -EINVAL;

nit: this doesn't say *what* value is unsupported, and I really
preferred the switch-case version, such as this:

diff --git a/arch/arm64/kvm/reset.c b/arch/arm64/kvm/reset.c
index 1f22b36a0eff..d267e4b1aec6 100644
--- a/arch/arm64/kvm/reset.c
+++ b/arch/arm64/kvm/reset.c

@@ -312,15 +312,18 @@ int kvm_set_ipa_limit(void)
 
 	switch (cpuid_feature_extract_unsigned_field(mmfr0, tgran_2)) {
 	default:
-	case 1:
+	case ID_AA64MMFR0_TGRAN_2_SUPPORTED_NONE:
 		kvm_err("PAGE_SIZE not supported at Stage-2, giving up\n");
 		return -EINVAL;
-	case 0:
+	case ID_AA64MMFR0_TGRAN_2_SUPPORTED_DEFAULT:
 		kvm_debug("PAGE_SIZE supported at Stage-2 (default)\n");
 		break;
-	case 2:
+	case ID_AA64MMFR0_TGRAN_2_SUPPORTED_MIN ... ID_AA64MMFR0_TGRAN_2_SUPPORTED_MAX:
 		kvm_debug("PAGE_SIZE supported at Stage-2 (advertised)\n");
 		break;
+	default:
+		kvm_err("Unsupported value for TGRAN_2, giving up\n");
+		return -EINVAL;
 	}
 
 	kvm_ipa_limit = id_aa64mmfr0_parange_to_phys_shift(parange);

Otherwise:

Acked-by: Marc Zyngier <maz@kernel.org>