On Thu, Feb 20, 2025 at 01:48:54PM +0000, Marc Zyngier wrote:
> With ARMv9.5, an implementation supporting Nested Virtualization
> is allowed to only support NV2, and to avoid supporting the old
> (and useless) ARMv8.3 variant.
>
> This is indicated by ID_AA64MMFR2_EL1.NV being 0 (as if NV wasn't
> implemented) and ID_AA64MMDR4_EL1.NV_frac being 1 (indicating that
typo: ID_AA64MMDR4_EL1 -> ID_AA64MMFR4_EL1
> NV2 is actually supported).
>
> Given that KVM only deals with NV2 and refuses to use the old NV,
> detecting NV2 or NV_frac is what we need to enable it.
>
> Signed-off-by: Marc Zyngier <maz@xxxxxxxxxx>
> ---
> arch/arm64/kernel/cpufeature.c | 15 +++++++++++++--
> 1 file changed, 13 insertions(+), 2 deletions(-)
>
> diff --git a/arch/arm64/kernel/cpufeature.c b/arch/arm64/kernel/cpufeature.c
> index d561cf3b8ac7b..2c198cd4f9405 100644
> --- a/arch/arm64/kernel/cpufeature.c
> +++ b/arch/arm64/kernel/cpufeature.c
> @@ -497,6 +497,7 @@ static const struct arm64_ftr_bits ftr_id_aa64mmfr3[] = {
>
> static const struct arm64_ftr_bits ftr_id_aa64mmfr4[] = {
> S_ARM64_FTR_BITS(FTR_HIDDEN, FTR_STRICT, FTR_LOWER_SAFE, ID_AA64MMFR4_EL1_E2H0_SHIFT, 4, 0),
> + ARM64_FTR_BITS(FTR_HIDDEN, FTR_STRICT, FTR_LOWER_SAFE, ID_AA64MMFR4_EL1_NV_frac_SHIFT, 4, 0),
> ARM64_FTR_END,
> };
>
> @@ -2162,7 +2163,7 @@ static bool has_nested_virt_support(const struct arm64_cpu_capabilities *cap,
> if (kvm_get_mode() != KVM_MODE_NV)
> return false;
>
> - if (!has_cpuid_feature(cap, scope)) {
> + if (!cpucap_multi_entry_cap_matches(cap, scope)) {
> pr_warn("unavailable: %s\n", cap->desc);
> return false;
> }
> @@ -2519,7 +2520,17 @@ static const struct arm64_cpu_capabilities arm64_features[] = {
> .capability = ARM64_HAS_NESTED_VIRT,
> .type = ARM64_CPUCAP_SYSTEM_FEATURE,
> .matches = has_nested_virt_support,
> - ARM64_CPUID_FIELDS(ID_AA64MMFR2_EL1, NV, NV2)
> + .match_list = (const struct arm64_cpu_capabilities []){
> + {
> + .matches = has_cpuid_feature,
> + ARM64_CPUID_FIELDS(ID_AA64MMFR2_EL1, NV, NV2)
> + },
> + {
> + .matches = has_cpuid_feature,
> + ARM64_CPUID_FIELDS(ID_AA64MMFR4_EL1, NV_frac, NV2_ONLY)
> + },
> + { /* Sentinel */ }
> + },
> },
> {
> .capability = ARM64_HAS_32BIT_EL0_DO_NOT_USE,
> --
> 2.39.2
>
