Re: [PATCH 03/13] arm64: Add ARM64_HAS_VIRT_HOST_EXTN feature

[Mark Rutland <mark.rutland@arm.com>]

On Wed, Jul 08, 2015 at 05:19:06PM +0100, Marc Zyngier wrote:
> Add a new ARM64_HAS_VIRT_HOST_EXTN features to indicate that the
> CPU has the ARMv8,1 VHE capability.

Nit: s/,/./

It's probably worth mentioning somewhere that we have to check CurrentEL
rather than a feature register in case some prior software dropped us to
EL1N (e.g. if we're a guest under this scheme).

Mark.

> 
> This will be used to trigger kernel patching in KVM.
> 
> Signed-off-by: Marc Zyngier <marc.zyngier@arm.com>
> ---
>  arch/arm64/include/asm/cpufeature.h |  3 ++-
>  arch/arm64/kernel/cpufeature.c      | 11 +++++++++++
>  2 files changed, 13 insertions(+), 1 deletion(-)
> 
> diff --git a/arch/arm64/include/asm/cpufeature.h b/arch/arm64/include/asm/cpufeature.h
> index c104421..6c3742d 100644
> --- a/arch/arm64/include/asm/cpufeature.h
> +++ b/arch/arm64/include/asm/cpufeature.h
> @@ -25,8 +25,9 @@
>  #define ARM64_WORKAROUND_DEVICE_LOAD_ACQUIRE	1
>  #define ARM64_WORKAROUND_845719			2
>  #define ARM64_HAS_SYSREG_GIC_CPUIF		3
> +#define ARM64_HAS_VIRT_HOST_EXTN		4
>  
> -#define ARM64_NCAPS				4
> +#define ARM64_NCAPS				5
>  
>  #ifndef __ASSEMBLY__
>  
> diff --git a/arch/arm64/kernel/cpufeature.c b/arch/arm64/kernel/cpufeature.c
> index 5ad86ce..e1dcd63 100644
> --- a/arch/arm64/kernel/cpufeature.c
> +++ b/arch/arm64/kernel/cpufeature.c
> @@ -21,6 +21,7 @@
>  #include <linux/types.h>
>  #include <asm/cpu.h>
>  #include <asm/cpufeature.h>
> +#include <asm/virt.h>
>  
>  static bool
>  has_id_aa64pfr0_feature(const struct arm64_cpu_capabilities *entry)
> @@ -31,6 +32,11 @@ has_id_aa64pfr0_feature(const struct arm64_cpu_capabilities *entry)
>  	return (val & entry->register_mask) == entry->register_value;
>  }
>  
> +static bool runs_at_el2(const struct arm64_cpu_capabilities *entry)
> +{
> +	return is_kernel_in_hyp_mode();
> +}
> +
>  static const struct arm64_cpu_capabilities arm64_features[] = {
>  	{
>  		.desc = "GIC system register CPU interface",
> @@ -39,6 +45,11 @@ static const struct arm64_cpu_capabilities arm64_features[] = {
>  		.register_mask = (0xf << 24),
>  		.register_value = (1 << 24),
>  	},
> +	{
> +		.desc = "Virtualization Host Extensions",
> +		.capability = ARM64_HAS_VIRT_HOST_EXTN,
> +		.matches = runs_at_el2,
> +	},
>  	{},
>  };
>  
> -- 
> 2.1.4
> 
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