Re: [PATCH v9 1/5] KVM: arm64: Add a vcpu flag to control ptrauth for guest

[Marc Zyngier]

On 12/04/2019 04:20, Amit Daniel Kachhap wrote:
> A per vcpu flag is added to check if pointer authentication is
> enabled for the vcpu or not. This flag may be enabled according to
> the necessary user policies and host capabilities.
> 
> This patch also adds a helper to check the flag.
> 
> Signed-off-by: Amit Daniel Kachhap <amit.kachhap@xxxxxxx>
> Cc: Mark Rutland <mark.rutland@xxxxxxx>
> Cc: Marc Zyngier <marc.zyngier@xxxxxxx>
> Cc: Christoffer Dall <christoffer.dall@xxxxxxx>
> Cc: kvmarm@xxxxxxxxxxxxxxxxxxxxx
> ---
> 
> Changes since v8:
> * Added a new per vcpu flag which will store Pointer Authentication enable
>   status instead of checking them again. [Dave Martin]
> 
>  arch/arm64/include/asm/kvm_host.h | 4 ++++
>  1 file changed, 4 insertions(+)
> 
> diff --git a/arch/arm64/include/asm/kvm_host.h b/arch/arm64/include/asm/kvm_host.h
> index 9d57cf8..31dbc7c 100644
> --- a/arch/arm64/include/asm/kvm_host.h
> +++ b/arch/arm64/include/asm/kvm_host.h
> @@ -355,10 +355,14 @@ struct kvm_vcpu_arch {
>  #define KVM_ARM64_HOST_SVE_ENABLED	(1 << 4) /* SVE enabled for EL0 */
>  #define KVM_ARM64_GUEST_HAS_SVE		(1 << 5) /* SVE exposed to guest */
>  #define KVM_ARM64_VCPU_SVE_FINALIZED	(1 << 6) /* SVE config completed */
> +#define KVM_ARM64_GUEST_HAS_PTRAUTH	(1 << 7) /* PTRAUTH exposed to guest */
>  
>  #define vcpu_has_sve(vcpu) (system_supports_sve() && \
>  			    ((vcpu)->arch.flags & KVM_ARM64_GUEST_HAS_SVE))
>  
> +#define vcpu_has_ptrauth(vcpu)	\
> +			((vcpu)->arch.flags & KVM_ARM64_GUEST_HAS_PTRAUTH)
> +

Just as for SVE, please first check that the system has PTRAUTH.
Something like:

		(cpus_have_const_cap(ARM64_HAS_GENERIC_AUTH_ARCH) && \
		 ((vcpu)->arch.flags & KVM_ARM64_GUEST_HAS_PTRAUTH))

This will save an extra load on unsuspecting CPUs thanks to the static
key embedded in the capability structure.

Thanks,

	M.
-- 
Jazz is not dead. It just smells funny...