Re: [PATCH 21/27] arm64/sve: KVM: Prevent guests from using SVE

[Marc Zyngier <marc.zyngier@xxxxxxx>]

On 09/08/17 13:05, Dave Martin wrote:
> Until KVM has full SVE support, guests must not be allowed to
> execute SVE instructions.
> 
> This patch enables the necessary traps, and also ensures that the
> traps are disabled again on exit from the guest so that the host
> can still use SVE if it wants to.
> 
> Signed-off-by: Dave Martin <Dave.Martin@xxxxxxx>
> ---
>  arch/arm64/include/asm/kvm_arm.h | 3 ++-
>  arch/arm64/kvm/hyp/switch.c      | 6 +++---
>  2 files changed, 5 insertions(+), 4 deletions(-)
> 
> diff --git a/arch/arm64/include/asm/kvm_arm.h b/arch/arm64/include/asm/kvm_arm.h
> index dbf0537..8a19651 100644
> --- a/arch/arm64/include/asm/kvm_arm.h
> +++ b/arch/arm64/include/asm/kvm_arm.h
> @@ -186,7 +186,7 @@
>  #define CPTR_EL2_TTA	(1 << 20)
>  #define CPTR_EL2_TFP	(1 << CPTR_EL2_TFP_SHIFT)
>  #define CPTR_EL2_TZ	(1 << 8)
> -#define CPTR_EL2_DEFAULT	0x000033ff
> +#define CPTR_EL2_DEFAULT	(0x000033ff & ~CPTR_EL2_TZ)

I must say I'm not overly fond of this construct. I'd rather introduce a
RES1 field that matches the v8.2 description, instead of this ugly
constant and something that clears it.

>  
>  /* Hyp Debug Configuration Register bits */
>  #define MDCR_EL2_TPMS		(1 << 14)
> @@ -237,5 +237,6 @@
>  
>  #define CPACR_EL1_FPEN		(3 << 20)
>  #define CPACR_EL1_TTA		(1 << 28)
> +#define CPACR_EL1_DEFAULT	(CPACR_EL1_FPEN | CPACR_EL1_ZEN_EL1EN)
>  
>  #endif /* __ARM64_KVM_ARM_H__ */
> diff --git a/arch/arm64/kvm/hyp/switch.c b/arch/arm64/kvm/hyp/switch.c
> index 35a90b8..951f3eb 100644
> --- a/arch/arm64/kvm/hyp/switch.c
> +++ b/arch/arm64/kvm/hyp/switch.c
> @@ -48,7 +48,7 @@ static void __hyp_text __activate_traps_vhe(void)
>  
>  	val = read_sysreg(cpacr_el1);
>  	val |= CPACR_EL1_TTA;
> -	val &= ~CPACR_EL1_FPEN;
> +	val &= ~(CPACR_EL1_FPEN | CPACR_EL1_ZEN);
>  	write_sysreg(val, cpacr_el1);
>  
>  	write_sysreg(__kvm_hyp_vector, vbar_el1);
> @@ -59,7 +59,7 @@ static void __hyp_text __activate_traps_nvhe(void)
>  	u64 val;
>  
>  	val = CPTR_EL2_DEFAULT;
> -	val |= CPTR_EL2_TTA | CPTR_EL2_TFP;
> +	val |= CPTR_EL2_TTA | CPTR_EL2_TFP | CPTR_EL2_TZ;
>  	write_sysreg(val, cptr_el2);
>  }
>  
> @@ -117,7 +117,7 @@ static void __hyp_text __deactivate_traps_vhe(void)
>  
>  	write_sysreg(mdcr_el2, mdcr_el2);
>  	write_sysreg(HCR_HOST_VHE_FLAGS, hcr_el2);
> -	write_sysreg(CPACR_EL1_FPEN, cpacr_el1);
> +	write_sysreg(CPACR_EL1_DEFAULT, cpacr_el1);
>  	write_sysreg(vectors, vbar_el1);
>  }
>  
> 

Thanks,

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