[PATCH v2] KVM: PPC: Book3s PR: Disable AIL mode with OPAL

[PATCH v2] KVM: PPC: Book3s PR: Disable AIL mode with OPAL

[Alexander Graf]

When we're using PR KVM we must not allow the CPU to take interrupts
in virtual mode, as the SLB does not contain host kernel mappings
when running inside the guest context.

To make sure we get good performance for non-KVM tasks but still
properly functioning PR KVM, let's just disable AIL whenever a vcpu
is scheduled in.

This is fundamentally different from how we deal with AIL on pSeries
type machines where we disable AIL for the whole machine as soon as
a single KVM VM is up.

The reason for that is easy - on pSeries we do not have control over
per-cpu configuration of AIL. We also don't want to mess with CPU hotplug
races and AIL configuration, so setting it per CPU is easier and more
flexible.

This patch fixes running PR KVM on POWER8 bare metal for me.

Signed-off-by: Alexander Graf <agraf@suse.de>

---

v1 -> v2:

  - Extend patch description

diff --git a/arch/powerpc/kvm/book3s_pr.c b/arch/powerpc/kvm/book3s_pr.c
index 3da412e..8ea7da4 100644
--- a/arch/powerpc/kvm/book3s_pr.c
+++ b/arch/powerpc/kvm/book3s_pr.c
@@ -71,6 +71,12 @@ static void kvmppc_core_vcpu_load_pr(struct kvm_vcpu *vcpu, int cpu)
 	svcpu->in_use = 0;
 	svcpu_put(svcpu);
 #endif
+
+	/* Disable AIL if supported */
+	if (cpu_has_feature(CPU_FTR_HVMODE) &&
+	    cpu_has_feature(CPU_FTR_ARCH_207S))
+		mtspr(SPRN_LPCR, mfspr(SPRN_LPCR) & ~LPCR_AIL);
+
 	vcpu->cpu = smp_processor_id();
 #ifdef CONFIG_PPC_BOOK3S_32
 	current->thread.kvm_shadow_vcpu = vcpu->arch.shadow_vcpu;
@@ -91,6 +97,12 @@ static void kvmppc_core_vcpu_put_pr(struct kvm_vcpu *vcpu)
 
 	kvmppc_giveup_ext(vcpu, MSR_FP | MSR_VEC | MSR_VSX);
 	kvmppc_giveup_fac(vcpu, FSCR_TAR_LG);
+
+	/* Enable AIL if supported */
+	if (cpu_has_feature(CPU_FTR_HVMODE) &&
+	    cpu_has_feature(CPU_FTR_ARCH_207S))
+		mtspr(SPRN_LPCR, mfspr(SPRN_LPCR) | LPCR_AIL_3);
+
 	vcpu->cpu = -1;
 }
 

Re: [PATCH v2] KVM: PPC: Book3s PR: Disable AIL mode with OPAL

[Paul Mackerras]

On Tue, Jun 17, 2014 at 12:03:58PM +0200, Alexander Graf wrote:
> When we're using PR KVM we must not allow the CPU to take interrupts
> in virtual mode, as the SLB does not contain host kernel mappings
> when running inside the guest context.
> 
> To make sure we get good performance for non-KVM tasks but still
> properly functioning PR KVM, let's just disable AIL whenever a vcpu
> is scheduled in.
> 
> This is fundamentally different from how we deal with AIL on pSeries
> type machines where we disable AIL for the whole machine as soon as
> a single KVM VM is up.
> 
> The reason for that is easy - on pSeries we do not have control over
> per-cpu configuration of AIL. We also don't want to mess with CPU hotplug
> races and AIL configuration, so setting it per CPU is easier and more
> flexible.
> 
> This patch fixes running PR KVM on POWER8 bare metal for me.
> 
> Signed-off-by: Alexander Graf <agraf@suse.de>

Acked-by: Paul Mackerras <paulus@samba.org>