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

[Amit Daniel Kachhap]

Hi,

On 4/17/19 2:05 PM, Marc Zyngier wrote:
> 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))

In the subsequent patches, vcpu->arch.flags is only set to 
KVM_ARM64_GUEST_HAS_PTRAUTH when all host capability check conditions 
matches such as system_supports_address_auth(), 
system_supports_generic_auth() so doing them again is repetitive in my view.

Thanks,
Amit D

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