[3/4] KVM: PPC: Book3S PR: Don't let PAPR guest set MSR hypervisor bit

Message ID 20180607080706.GC13401@fergus.ozlabs.ibm.com
State Accepted
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Series
  • [1/4] KVM: PPC: Book3S PR: Fix MSR setting when delivering interrupts
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Commit Message

Paul Mackerras June 7, 2018, 8:07 a.m.
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>
---
 arch/powerpc/kvm/book3s_pr.c | 4 ++++
 1 file changed, 4 insertions(+)

Patch

diff --git a/arch/powerpc/kvm/book3s_pr.c b/arch/powerpc/kvm/book3s_pr.c
index 5c708d6a44fb..c36c8ef3dfb0 100644
--- 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