Re: [PATCH v1 3/5] KVM: arm64: Use the appropriate feature trap register when activating traps

[Oliver Upton <oliver.upton@linux.dev>]

On Wed, Jul 19, 2023 at 04:06:37PM +0100, Fuad Tabba wrote:
> Use the architectural feature trap/control register that
> corresponds to the current KVM mode, i.e., CPTR_EL2 or CPACR_EL1,
> when activating traps.
> 
> Signed-off-by: Fuad Tabba <tabba@google.com>
> ---
>  arch/arm64/kvm/hyp/nvhe/switch.c | 6 +++++-
>  1 file changed, 5 insertions(+), 1 deletion(-)
> 
> diff --git a/arch/arm64/kvm/hyp/nvhe/switch.c b/arch/arm64/kvm/hyp/nvhe/switch.c
> index 0a6271052def..e5ea517bab9c 100644
> --- a/arch/arm64/kvm/hyp/nvhe/switch.c
> +++ b/arch/arm64/kvm/hyp/nvhe/switch.c
> @@ -63,7 +63,11 @@ static void __activate_traps(struct kvm_vcpu *vcpu)
>  		__activate_traps_fpsimd32(vcpu);
>  	}
>  
> -	write_sysreg(val, cptr_el2);
> +	if (has_hvhe())
> +		write_sysreg(val, cpacr_el1);
> +	else
> +		write_sysreg(val, cptr_el2);
> +

Does it make sense to have an accessor that's shared with
kvm_reset_cptr_el2()? Due to the lack of synchronization between the
aliases we really want to avoid inconsistently using one or the other.

-- 
Thanks,
Oliver