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

Marc Zyngier
2017-08-15T16:31:37Z

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@arm.com>
> ---
> 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...