Makes a lot of sense and it also improves the skey performane for the hlp patch series.
Does it make sense to let this be part of the next version of the host large pages
series or shall I take this patch directly?
On 07/20/2018 04:16 PM, Janosch Frank wrote:
> Let's introduce an explicit check if skeys have already been enabled
> for the vcpu, so we don't have to check the mm context if we don't have
> the storage key facility.
>
> This let's us check for enablement without having to take the mm
> semaphore and thus speedup skey emulation.
>
> Signed-off-by: Janosch Frank <frankja@xxxxxxxxxxxxx>
> Acked-by: Farhan Ali <alifm@xxxxxxxxxxxxx>
> ---
> arch/s390/include/asm/kvm_host.h | 1 +
> arch/s390/kvm/priv.c | 12 ++++--------
> 2 files changed, 5 insertions(+), 8 deletions(-)
>
> diff --git a/arch/s390/include/asm/kvm_host.h b/arch/s390/include/asm/kvm_host.h
> index a2188e309bd6..2916f0a5585c 100644
> --- a/arch/s390/include/asm/kvm_host.h
> +++ b/arch/s390/include/asm/kvm_host.h
> @@ -655,6 +655,7 @@ struct kvm_vcpu_arch {
> seqcount_t cputm_seqcount;
> __u64 cputm_start;
> bool gs_enabled;
> + bool skey_enabled;
> };
>
> struct kvm_vm_stat {
> diff --git a/arch/s390/kvm/priv.c b/arch/s390/kvm/priv.c
> index 83c678266588..54493c587a9e 100644
> --- a/arch/s390/kvm/priv.c
> +++ b/arch/s390/kvm/priv.c
> @@ -205,13 +205,10 @@ static int handle_store_cpu_address(struct kvm_vcpu *vcpu)
> int kvm_s390_skey_check_enable(struct kvm_vcpu *vcpu)
> {
> int rc;
> - struct kvm_s390_sie_block *sie_block = vcpu->arch.sie_block;
>
> trace_kvm_s390_skey_related_inst(vcpu);
> /* Already enabled? */
> - if (vcpu->kvm->arch.use_skf &&
> - !(sie_block->ictl & (ICTL_ISKE | ICTL_SSKE | ICTL_RRBE)) &&
> - !kvm_s390_test_cpuflags(vcpu, CPUSTAT_KSS))
> + if (vcpu->arch.skey_enabled)
> return 0;
>
> rc = s390_enable_skey();
> @@ -221,10 +218,9 @@ int kvm_s390_skey_check_enable(struct kvm_vcpu *vcpu)
>
> if (kvm_s390_test_cpuflags(vcpu, CPUSTAT_KSS))
> kvm_s390_clear_cpuflags(vcpu, CPUSTAT_KSS);
> - if (!vcpu->kvm->arch.use_skf)
> - sie_block->ictl |= ICTL_ISKE | ICTL_SSKE | ICTL_RRBE;
> - else
> - sie_block->ictl &= ~(ICTL_ISKE | ICTL_SSKE | ICTL_RRBE);
> + if (vcpu->kvm->arch.use_skf)
> + vcpu->arch.sie_block->ictl &= ~(ICTL_ISKE | ICTL_SSKE | ICTL_RRBE);
> + vcpu->arch.skey_enabled = true;
> return 0;
> }
>
>
