KVM: PPC: Book3S PR: Don't let PAPR guest set MSR hypervisor bit

PAPR guests run in supervisor mode and should not be able to set the
MSR HV (hypervisor mode) bit or clear the ME (machine check enable)
bit by mtmsrd or any other means.  To enforce this, we force MSR_HV
off and MSR_ME on in kvmppc_set_msr_pr.  Without this, the guest
can appear to be in hypervisor mode to itself and to userspace.
This has been observed to cause a crash in QEMU when it tries to
deliver a system reset interrupt to the guest.

Signed-off-by: Paul Mackerras <paulus@ozlabs.org>

diff --git a/arch/powerpc/kvm/book3s_pr.c b/arch/powerpc/kvm/book3s_pr.c
index e8036dd..5c99b84 100644 (file)
--- a/arch/powerpc/kvm/book3s_pr.c
+++ b/arch/powerpc/kvm/book3s_pr.c
@@ -456,6 +456,10 @@ static void kvmppc_set_msr_pr(struct kvm_vcpu *vcpu, u64 msr)
 {
        ulong old_msr;
 
+       /* For PAPR guest, make sure MSR reflects guest mode */
+       if (vcpu->arch.papr_enabled)
+               msr = (msr & ~MSR_HV) | MSR_ME;
+
 #ifdef EXIT_DEBUG
        printk(KERN_INFO "KVM: Set MSR to 0x%llx\n", msr);
 #endif