KVM: PPC: Convert MSR to shared page

One of the most obvious registers to share with the guest directly is the
MSR. The MSR contains the "interrupts enabled" flag which the guest has to
toggle in critical sections.

So in order to bring the overhead of interrupt en- and disabling down, let's
put msr into the shared page. Keep in mind that even though you can fully read
its contents, writing to it doesn't always update all state. There are a few
safe fields that don't require hypervisor interaction. See the documentation
for a list of MSR bits that are safe to be set from inside the guest.

Signed-off-by: Alexander Graf <agraf@suse.de>
Signed-off-by: Avi Kivity <avi@redhat.com>

1 files changed, 5 insertions, 4 deletions

diff --git a/arch/powerpc/kvm/book3s_emulate.c b/arch/powerpc/kvm/book3s_emulate.c
index c85f906038ce..35d3c16b2938 100644
--- a/arch/powerpc/kvm/book3s_emulate.c
+++ b/arch/powerpc/kvm/book3s_emulate.c
@@ -86,14 +86,15 @@ int kvmppc_core_emulate_op(struct kvm_run *run, struct kvm_vcpu *vcpu,
         case 31:
                 switch (get_xop(inst)) {
                 case OP_31_XOP_MFMSR:
-                        kvmppc_set_gpr(vcpu, get_rt(inst), vcpu->arch.msr);
+                        kvmppc_set_gpr(vcpu, get_rt(inst),
+                                       vcpu->arch.shared->msr);
                         break;
                 case OP_31_XOP_MTMSRD:
                 {
                         ulong rs = kvmppc_get_gpr(vcpu, get_rs(inst));
                         if (inst & 0x10000) {
-                                vcpu->arch.msr &= ~(MSR_RI | MSR_EE);
-                                vcpu->arch.msr |= rs & (MSR_RI | MSR_EE);
+                                vcpu->arch.shared->msr &= ~(MSR_RI | MSR_EE);
+                                vcpu->arch.shared->msr |= rs & (MSR_RI | MSR_EE);
                         } else
                                 kvmppc_set_msr(vcpu, rs);
                         break;
@@ -204,7 +205,7 @@ int kvmppc_core_emulate_op(struct kvm_run *run, struct kvm_vcpu *vcpu,
                                 ra = kvmppc_get_gpr(vcpu, get_ra(inst));
 
                         addr = (ra + rb) & ~31ULL;
-                        if (!(vcpu->arch.msr & MSR_SF))
+                        if (!(vcpu->arch.shared->msr & MSR_SF))
                                 addr &= 0xffffffff;
                         vaddr = addr;