From f9208427f72e6cb52c71767af3bf8c14c43c27ac Mon Sep 17 00:00:00 2001 From: Bharat Bhushan Date: Thu, 13 Oct 2011 15:17:08 +0530 Subject: [PATCH] PPC: Fix race in mtmsr paravirt implementation The current implementation of mtmsr and mtmsrd are racy in that it does: * check (int_pending == 0) ---> host sets int_pending = 1 <--- * write shared page * done while instead we should check for int_pending after the shared page is written. Signed-off-by: Bharat Bhushan Signed-off-by: Alexander Graf Signed-off-by: Avi Kivity --- arch/powerpc/kernel/kvm_emul.S | 10 ++++------ 1 file changed, 4 insertions(+), 6 deletions(-) diff --git a/arch/powerpc/kernel/kvm_emul.S b/arch/powerpc/kernel/kvm_emul.S index f2b1b2523e61..3d64c5704fd5 100644 --- a/arch/powerpc/kernel/kvm_emul.S +++ b/arch/powerpc/kernel/kvm_emul.S @@ -167,6 +167,9 @@ maybe_stay_in_guest: kvm_emulate_mtmsr_reg2: ori r30, r0, 0 + /* Put MSR into magic page because we don't call mtmsr */ + STL64(r30, KVM_MAGIC_PAGE + KVM_MAGIC_MSR, 0) + /* Check if we have to fetch an interrupt */ lwz r31, (KVM_MAGIC_PAGE + KVM_MAGIC_INT)(0) cmpwi r31, 0 @@ -174,15 +177,10 @@ kvm_emulate_mtmsr_reg2: /* Check if we may trigger an interrupt */ andi. r31, r30, MSR_EE - beq no_mtmsr - - b do_mtmsr + bne do_mtmsr no_mtmsr: - /* Put MSR into magic page because we don't call mtmsr */ - STL64(r30, KVM_MAGIC_PAGE + KVM_MAGIC_MSR, 0) - SCRATCH_RESTORE /* Go back to caller */