Re: [PATCH 05/10] KVM: arm64: Rework SVE host-save/guest-restore

[Will Deacon <will@kernel.org>]

On Tue, Mar 16, 2021 at 10:13:07AM +0000, Marc Zyngier wrote:
> In order to keep the code readable, move the host-save/guest-restore
> sequences in their own functions, with the following changes:
> - the hypervisor ZCR is now set from C code
> - ZCR_EL2 is always used as the EL2 accessor
> 
> This results in some minor assembler macro rework.
> No functional change intended.
> 
> Signed-off-by: Marc Zyngier <maz@kernel.org>
> ---
>  arch/arm64/include/asm/fpsimdmacros.h   |  8 +++--
>  arch/arm64/include/asm/kvm_hyp.h        |  2 +-
>  arch/arm64/kvm/hyp/fpsimd.S             |  2 +-
>  arch/arm64/kvm/hyp/include/hyp/switch.h | 41 +++++++++++++++----------
>  4 files changed, 33 insertions(+), 20 deletions(-)

[...]

> diff --git a/arch/arm64/kvm/hyp/include/hyp/switch.h b/arch/arm64/kvm/hyp/include/hyp/switch.h
> index fb68271c1a0f..d34dc220a1ce 100644
> --- a/arch/arm64/kvm/hyp/include/hyp/switch.h
> +++ b/arch/arm64/kvm/hyp/include/hyp/switch.h
> @@ -196,6 +196,25 @@ static inline bool __populate_fault_info(struct kvm_vcpu *vcpu)
>  	return true;
>  }
>  
> +static inline void __hyp_sve_save_host(struct kvm_vcpu *vcpu)
> +{
> +	struct thread_struct *thread;
> +
> +	thread = container_of(vcpu->arch.host_fpsimd_state, struct thread_struct,
> +			      uw.fpsimd_state);
> +
> +	__sve_save_state(sve_pffr(thread), &vcpu->arch.host_fpsimd_state->fpsr);
> +}
> +
> +static inline void __hyp_sve_restore_guest(struct kvm_vcpu *vcpu)
> +{
> +	if (read_sysreg_s(SYS_ZCR_EL2) != (vcpu_sve_vq(vcpu) - 1))

Strictly speaking, we should probably be extracting the LEN field from
ZCR_EL2, otherwise this has the potential to go horribly wrong if any of
the RES0 bits are allocated in future.

Other than that:

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

Will