Hey Marc,
I'm an idiot and was responding to v1. Here's the same damn comment, but
on v2!
On Fri, May 26, 2023 at 03:33:35PM +0100, Marc Zyngier wrote:
> Expose a capability keying the hVHE feature as well as a new
> predicate testing it. Nothing is so far using it, and nothing
> is enabling it yet.
>
> Signed-off-by: Marc Zyngier <maz@xxxxxxxxxx>
> ---
> arch/arm64/include/asm/cpufeature.h | 1 +
> arch/arm64/include/asm/virt.h | 8 ++++++++
> arch/arm64/kernel/cpufeature.c | 15 +++++++++++++++
> arch/arm64/tools/cpucaps | 1 +
> 4 files changed, 25 insertions(+)
>
> diff --git a/arch/arm64/include/asm/cpufeature.h b/arch/arm64/include/asm/cpufeature.h
> index bc1009890180..3d4b547ae312 100644
> --- a/arch/arm64/include/asm/cpufeature.h
> +++ b/arch/arm64/include/asm/cpufeature.h
> @@ -16,6 +16,7 @@
> #define cpu_feature(x) KERNEL_HWCAP_ ## x
>
> #define ARM64_SW_FEATURE_OVERRIDE_NOKASLR 0
> +#define ARM64_SW_FEATURE_OVERRIDE_HVHE 4
>
> #ifndef __ASSEMBLY__
>
> diff --git a/arch/arm64/include/asm/virt.h b/arch/arm64/include/asm/virt.h
> index 91029709d133..5f84a87a6a2d 100644
> --- a/arch/arm64/include/asm/virt.h
> +++ b/arch/arm64/include/asm/virt.h
> @@ -145,6 +145,14 @@ static __always_inline bool is_protected_kvm_enabled(void)
> return cpus_have_final_cap(ARM64_KVM_PROTECTED_MODE);
> }
>
> +static __always_inline bool has_hvhe(void)
> +{
> + if (is_vhe_hyp_code())
> + return false;
> +
> + return cpus_have_final_cap(ARM64_KVM_HVHE);
> +}
> +
> static inline bool is_hyp_nvhe(void)
> {
> return is_hyp_mode_available() && !is_kernel_in_hyp_mode();
> diff --git a/arch/arm64/kernel/cpufeature.c b/arch/arm64/kernel/cpufeature.c
> index 2d2b7bb5fa0c..04ef60571b37 100644
> --- a/arch/arm64/kernel/cpufeature.c
> +++ b/arch/arm64/kernel/cpufeature.c
> @@ -1998,6 +1998,15 @@ static bool has_nested_virt_support(const struct arm64_cpu_capabilities *cap,
> return true;
> }
>
> +static bool hvhe_possible(const struct arm64_cpu_capabilities *entry,
> + int __unused)
> +{
> + u64 val;
> +
> + val = arm64_sw_feature_override.val & arm64_sw_feature_override.mask;
> + return cpuid_feature_extract_unsigned_field(val, ARM64_SW_FEATURE_OVERRIDE_HVHE);
> +}
Does this need to test ID_AA64MMFR1_EL1.VH as well? Otherwise I don't
see what would stop us from attempting hVHE on a system with asymmetric
support for VHE, as the software override was only evaluated on the boot
CPU.
> #ifdef CONFIG_ARM64_PAN
> static void cpu_enable_pan(const struct arm64_cpu_capabilities *__unused)
> {
> @@ -2643,6 +2652,12 @@ static const struct arm64_cpu_capabilities arm64_features[] = {
> .cpu_enable = cpu_enable_dit,
> ARM64_CPUID_FIELDS(ID_AA64PFR0_EL1, DIT, IMP)
> },
> + {
> + .desc = "VHE for hypervisor only",
> + .capability = ARM64_KVM_HVHE,
> + .type = ARM64_CPUCAP_STRICT_BOOT_CPU_FEATURE,
> + .matches = hvhe_possible,
> + },
> {},
> };
>
> diff --git a/arch/arm64/tools/cpucaps b/arch/arm64/tools/cpucaps
> index 40ba95472594..3c23a55d7c2f 100644
> --- a/arch/arm64/tools/cpucaps
> +++ b/arch/arm64/tools/cpucaps
> @@ -47,6 +47,7 @@ HAS_TLB_RANGE
> HAS_VIRT_HOST_EXTN
> HAS_WFXT
> HW_DBM
> +KVM_HVHE
> KVM_PROTECTED_MODE
> MISMATCHED_CACHE_TYPE
> MTE
> --
> 2.34.1
>
--
Thanks,
Oliver
