KVM: powerpc: Map guest userspace with TID=0 mappings

When we use TID=N userspace mappings, we must ensure that kernel mappings have
been destroyed when entering userspace. Using TID=1/TID=0 for kernel/user
mappings and running userspace with PID=0 means that userspace can't access the
kernel mappings, but the kernel can directly access userspace.

The net is that we don't need to flush the TLB on privilege switches, but we do
on guest context switches (which are far more infrequent). Guest boot time
performance improvement: about 30%.

Signed-off-by: Hollis Blanchard <hollisb@us.ibm.com>
Signed-off-by: Avi Kivity <avi@qumranet.com>

1 files changed, 2 insertions, 0 deletions

diff --git a/arch/powerpc/kvm/booke_guest.c b/arch/powerpc/kvm/booke_guest.c
index 3cca079975e1..7b2591e26bae 100644
--- a/arch/powerpc/kvm/booke_guest.c
+++ b/arch/powerpc/kvm/booke_guest.c
@@ -486,6 +486,8 @@ int kvm_arch_vcpu_setup(struct kvm_vcpu *vcpu)
         vcpu->arch.msr = 0;
         vcpu->arch.gpr[1] = (16<<20) - 8; /* -8 for the callee-save LR slot */
 
+        vcpu->arch.shadow_pid = 1;
+
         /* Eye-catching number so we know if the guest takes an interrupt
          * before it's programmed its own IVPR. */
         vcpu->arch.ivpr = 0x55550000;