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, 4 insertions, 3 deletions

diff --git a/arch/powerpc/kvm/book3s_paired_singles.c b/arch/powerpc/kvm/book3s_paired_singles.c
index 474f2e24050a..626e6efaa79f 100644
--- a/arch/powerpc/kvm/book3s_paired_singles.c
+++ b/arch/powerpc/kvm/book3s_paired_singles.c
@@ -165,9 +165,10 @@ static inline void kvmppc_sync_qpr(struct kvm_vcpu *vcpu, int rt)
 static void kvmppc_inject_pf(struct kvm_vcpu *vcpu, ulong eaddr, bool is_store)
 {
         u64 dsisr;
+        struct kvm_vcpu_arch_shared *shared = vcpu->arch.shared;
 
-        vcpu->arch.msr = kvmppc_set_field(vcpu->arch.msr, 33, 36, 0);
-        vcpu->arch.msr = kvmppc_set_field(vcpu->arch.msr, 42, 47, 0);
+        shared->msr = kvmppc_set_field(shared->msr, 33, 36, 0);
+        shared->msr = kvmppc_set_field(shared->msr, 42, 47, 0);
         vcpu->arch.dear = eaddr;
         /* Page Fault */
         dsisr = kvmppc_set_field(0, 33, 33, 1);
@@ -658,7 +659,7 @@ int kvmppc_emulate_paired_single(struct kvm_run *run, struct kvm_vcpu *vcpu)
         if (!kvmppc_inst_is_paired_single(vcpu, inst))
                 return EMULATE_FAIL;
 
-        if (!(vcpu->arch.msr & MSR_FP)) {
+        if (!(vcpu->arch.shared->msr & MSR_FP)) {
                 kvmppc_book3s_queue_irqprio(vcpu, BOOK3S_INTERRUPT_FP_UNAVAIL);
                 return EMULATE_AGAIN;
         }