[RFC PATCH 38/43] KVM: PPC: Book3S HV P9: Test dawr_enabled() before saving host DAWR SPRs

[Fabiano Rosas]

Nicholas Piggin <npiggin at gmail.com> writes:

> Some of the DAWR SPR access is already predicated on dawr_enabled(),
> apply this to the remainder of the accesses.
>
> Signed-off-by: Nicholas Piggin <npiggin at gmail.com>
> ---
>  arch/powerpc/kvm/book3s_hv_p9_entry.c | 34 ++++++++++++++++-----------
>  1 file changed, 20 insertions(+), 14 deletions(-)
>
> diff --git a/arch/powerpc/kvm/book3s_hv_p9_entry.c b/arch/powerpc/kvm/book3s_hv_p9_entry.c
> index 7aa72efcac6c..f305d1d6445c 100644
> --- a/arch/powerpc/kvm/book3s_hv_p9_entry.c
> +++ b/arch/powerpc/kvm/book3s_hv_p9_entry.c
> @@ -638,13 +638,16 @@ int kvmhv_vcpu_entry_p9(struct kvm_vcpu *vcpu, u64 time_limit, unsigned long lpc
>
>  	host_hfscr = mfspr(SPRN_HFSCR);
>  	host_ciabr = mfspr(SPRN_CIABR);
> -	host_dawr0 = mfspr(SPRN_DAWR0);
> -	host_dawrx0 = mfspr(SPRN_DAWRX0);
>  	host_psscr = mfspr(SPRN_PSSCR);
>  	host_pidr = mfspr(SPRN_PID);
> -	if (cpu_has_feature(CPU_FTR_DAWR1)) {
> -		host_dawr1 = mfspr(SPRN_DAWR1);
> -		host_dawrx1 = mfspr(SPRN_DAWRX1);
> +
> +	if (dawr_enabled()) {
> +		host_dawr0 = mfspr(SPRN_DAWR0);
> +		host_dawrx0 = mfspr(SPRN_DAWRX0);
> +		if (cpu_has_feature(CPU_FTR_DAWR1)) {
> +			host_dawr1 = mfspr(SPRN_DAWR1);
> +			host_dawrx1 = mfspr(SPRN_DAWRX1);

The userspace needs to enable DAWR1 via KVM_CAP_PPC_DAWR1. That cap is
not even implemented in QEMU currently, so we never allow the guest to
set vcpu->arch.dawr1. If we check for kvm->arch.dawr1_enabled instead of
the CPU feature, we could shave some more time here.

> +		}
>  	}
>
>  	local_paca->kvm_hstate.host_purr = mfspr(SPRN_PURR);
> @@ -951,15 +954,18 @@ int kvmhv_vcpu_entry_p9(struct kvm_vcpu *vcpu, u64 time_limit, unsigned long lpc
>  	mtspr(SPRN_HFSCR, host_hfscr);
>  	if (vcpu->arch.ciabr != host_ciabr)
>  		mtspr(SPRN_CIABR, host_ciabr);
> -	if (vcpu->arch.dawr0 != host_dawr0)
> -		mtspr(SPRN_DAWR0, host_dawr0);
> -	if (vcpu->arch.dawrx0 != host_dawrx0)
> -		mtspr(SPRN_DAWRX0, host_dawrx0);
> -	if (cpu_has_feature(CPU_FTR_DAWR1)) {
> -		if (vcpu->arch.dawr1 != host_dawr1)
> -			mtspr(SPRN_DAWR1, host_dawr1);
> -		if (vcpu->arch.dawrx1 != host_dawrx1)
> -			mtspr(SPRN_DAWRX1, host_dawrx1);
> +
> +	if (dawr_enabled()) {
> +		if (vcpu->arch.dawr0 != host_dawr0)
> +			mtspr(SPRN_DAWR0, host_dawr0);
> +		if (vcpu->arch.dawrx0 != host_dawrx0)
> +			mtspr(SPRN_DAWRX0, host_dawrx0);
> +		if (cpu_has_feature(CPU_FTR_DAWR1)) {
> +			if (vcpu->arch.dawr1 != host_dawr1)
> +				mtspr(SPRN_DAWR1, host_dawr1);
> +			if (vcpu->arch.dawrx1 != host_dawrx1)
> +				mtspr(SPRN_DAWRX1, host_dawrx1);
> +		}
>  	}
>
>  	if (vc->dpdes)