[PATCH 4.4.x] KVM: PPC: Book3S HV: Context-switch EBB registers properly

[PATCH 4.4.x] KVM: PPC: Book3S HV: Context-switch EBB registers properly

[Paul Mackerras]

commit ca8efa1df1d15a1795a2da57f9f6aada6ed6b946 upstream.

This adds code to save the values of three SPRs (special-purpose
registers) used by userspace to control event-based branches (EBBs),
which are essentially interrupts that get delivered directly to
userspace.  These registers are loaded up with guest values when
entering the guest, and their values are saved when exiting the
guest, but we were not saving the host values and restoring them
before going back to userspace.

On POWER8 this would only affect userspace programs which explicitly
request the use of EBBs and also use the KVM_RUN ioctl, since the
only source of EBBs on POWER8 is the PMU, and there is an explicit
enable bit in the PMU registers (and those PMU registers do get
properly context-switched between host and guest).  On POWER9 there
is provision for externally-generated EBBs, and these are not subject
to the control in the PMU registers.

Since these registers only affect userspace, we can save them when
we first come in from userspace and restore them before returning to
userspace, rather than saving/restoring the host values on every
guest entry/exit.  Similarly, we don't need to worry about their
values on offline secondary threads since they execute in the context
of the idle task, which never executes in userspace.

Fixes: b005255e12a3 ("KVM: PPC: Book3S HV: Context-switch new POWER8 SPRs", 2014-01-08)
Cc: stable@vger.kernel.org # v3.14+
Signed-off-by: Paul Mackerras <paulus@ozlabs.org>
---
 arch/powerpc/kvm/book3s_hv.c | 16 ++++++++++++++++
 1 file changed, 16 insertions(+)

diff --git a/arch/powerpc/kvm/book3s_hv.c b/arch/powerpc/kvm/book3s_hv.c
index ed671bd0690d..a3021e6ee14d 100644
--- a/arch/powerpc/kvm/book3s_hv.c
+++ b/arch/powerpc/kvm/book3s_hv.c
@@ -1950,6 +1950,7 @@ static int kvmppc_vcpu_run_hv(struct kvm_run *run, struct kvm_vcpu *vcpu)
 {
 	int r;
 	int srcu_idx;
+	unsigned long ebb_regs[3] = {};	/* shut up GCC */
 
 	if (!vcpu->arch.sane) {
 		run->exit_reason = KVM_EXIT_INTERNAL_ERROR;
@@ -1999,6 +2000,14 @@ static int kvmppc_vcpu_run_hv(struct kvm_run *run, struct kvm_vcpu *vcpu)
 	flush_fp_to_thread(current);
 	flush_altivec_to_thread(current);
 	flush_vsx_to_thread(current);
+
+	/* Save userspace EBB register values */
+	if (cpu_has_feature(CPU_FTR_ARCH_207S)) {
+		ebb_regs[0] = mfspr(SPRN_EBBHR);
+		ebb_regs[1] = mfspr(SPRN_EBBRR);
+		ebb_regs[2] = mfspr(SPRN_BESCR);
+	}
+
 	vcpu->arch.wqp = &vcpu->arch.vcore->wq;
 	vcpu->arch.pgdir = current->mm->pgd;
 	vcpu->arch.state = KVMPPC_VCPU_BUSY_IN_HOST;
@@ -2018,6 +2027,13 @@ static int kvmppc_vcpu_run_hv(struct kvm_run *run, struct kvm_vcpu *vcpu)
 		}
 	} while (is_kvmppc_resume_guest(r));
 
+	/* Restore userspace EBB register values */
+	if (cpu_has_feature(CPU_FTR_ARCH_207S)) {
+		mtspr(SPRN_EBBHR, ebb_regs[0]);
+		mtspr(SPRN_EBBRR, ebb_regs[1]);
+		mtspr(SPRN_BESCR, ebb_regs[2]);
+	}
+
  out:
 	vcpu->arch.state = KVMPPC_VCPU_NOTREADY;
 	atomic_dec(&vcpu->kvm->arch.vcpus_running);
-- 
2.11.0

Re: [PATCH 4.4.x] KVM: PPC: Book3S HV: Context-switch EBB registers properly

[Greg KH]

On Wed, Jul 26, 2017 at 09:46:15AM +1000, Paul Mackerras wrote:
> commit ca8efa1df1d15a1795a2da57f9f6aada6ed6b946 upstream.
> 
> This adds code to save the values of three SPRs (special-purpose
> registers) used by userspace to control event-based branches (EBBs),
> which are essentially interrupts that get delivered directly to
> userspace.  These registers are loaded up with guest values when
> entering the guest, and their values are saved when exiting the
> guest, but we were not saving the host values and restoring them
> before going back to userspace.
> 
> On POWER8 this would only affect userspace programs which explicitly
> request the use of EBBs and also use the KVM_RUN ioctl, since the
> only source of EBBs on POWER8 is the PMU, and there is an explicit
> enable bit in the PMU registers (and those PMU registers do get
> properly context-switched between host and guest).  On POWER9 there
> is provision for externally-generated EBBs, and these are not subject
> to the control in the PMU registers.
> 
> Since these registers only affect userspace, we can save them when
> we first come in from userspace and restore them before returning to
> userspace, rather than saving/restoring the host values on every
> guest entry/exit.  Similarly, we don't need to worry about their
> values on offline secondary threads since they execute in the context
> of the idle task, which never executes in userspace.
> 
> Fixes: b005255e12a3 ("KVM: PPC: Book3S HV: Context-switch new POWER8 SPRs", 2014-01-08)
> Cc: stable@vger.kernel.org # v3.14+
> Signed-off-by: Paul Mackerras <paulus@ozlabs.org>
> ---
>  arch/powerpc/kvm/book3s_hv.c | 16 ++++++++++++++++
>  1 file changed, 16 insertions(+)

Now applied, thanks.

greg k-h