[PATCH v2 10/11] KVM: arm64: Save/restore SVE state for nVHE

[Will Deacon]

On Thu, Mar 18, 2021 at 12:25:31PM +0000, Marc Zyngier wrote:
> Implement the SVE save/restore for nVHE, following a similar
> logic to that of the VHE implementation:
> 
> - the SVE state is switched on trap from EL1 to EL2
> 
> - no further changes to ZCR_EL2 occur as long as the guest isn't
>   preempted or exit to userspace
> 
> - ZCR_EL2 is reset to its default value on the first SVE access from
>   the host EL1, and ZCR_EL1 restored to the default guest value in
>   vcpu_put()
> 
> Signed-off-by: Marc Zyngier <maz at kernel.org>
> ---
>  arch/arm64/kvm/fpsimd.c                 | 10 +++++--
>  arch/arm64/kvm/hyp/include/hyp/switch.h | 37 +++++++++----------------
>  arch/arm64/kvm/hyp/nvhe/switch.c        |  4 +--
>  3 files changed, 23 insertions(+), 28 deletions(-)
> 
> diff --git a/arch/arm64/kvm/fpsimd.c b/arch/arm64/kvm/fpsimd.c
> index 14ea05c5134a..5621020b28de 100644
> --- a/arch/arm64/kvm/fpsimd.c
> +++ b/arch/arm64/kvm/fpsimd.c
> @@ -121,11 +121,17 @@ void kvm_arch_vcpu_put_fp(struct kvm_vcpu *vcpu)
>  	local_irq_save(flags);
>  
>  	if (vcpu->arch.flags & KVM_ARM64_FP_ENABLED) {
> -		if (guest_has_sve)
> +		if (guest_has_sve) {
>  			__vcpu_sys_reg(vcpu, ZCR_EL1) = read_sysreg_el1(SYS_ZCR);
>  
> +			/* Restore the VL that was saved when bound to the CPU */
> +			if (!has_vhe())
> +				sve_cond_update_zcr_vq(vcpu_sve_max_vq(vcpu) - 1,
> +						       SYS_ZCR_EL1);

You end up reading ZCR_EL1 twice here, but it's probably not the end of the
world.

Anyway:

Acked-by: Will Deacon <will at kernel.org>

Will