1 files changed, 26 insertions, 6 deletions

diff --git a/arch/powerpc/kernel/idle_book3s.S b/arch/powerpc/kernel/idle_book3s.S
index bd739fed26e3..0d8712a835d2 100644
--- a/arch/powerpc/kernel/idle_book3s.S
+++ b/arch/powerpc/kernel/idle_book3s.S
@@ -163,12 +163,6 @@ _GLOBAL(pnv_powersave_common)
         std     r9,_MSR(r1)
         std     r1,PACAR1(r13)
 
-#ifdef CONFIG_KVM_BOOK3S_HV_POSSIBLE
-        /* Tell KVM we're entering idle */
-        li      r4,KVM_HWTHREAD_IN_IDLE
-        stb     r4,HSTATE_HWTHREAD_STATE(r13)
-#endif
-
         /*
          * Go to real mode to do the nap, as required by the architecture.
          * Also, we need to be in real mode before setting hwthread_state,
@@ -185,6 +179,26 @@ _GLOBAL(pnv_powersave_common)
 
         .globl pnv_enter_arch207_idle_mode
 pnv_enter_arch207_idle_mode:
+#ifdef CONFIG_KVM_BOOK3S_HV_POSSIBLE
+        /* Tell KVM we're entering idle */
+        li      r4,KVM_HWTHREAD_IN_IDLE
+        /******************************************************/
+        /*  N O T E   W E L L    ! ! !    N O T E   W E L L   */
+        /* The following store to HSTATE_HWTHREAD_STATE(r13)  */
+        /* MUST occur in real mode, i.e. with the MMU off,    */
+        /* and the MMU must stay off until we clear this flag */
+        /* and test HSTATE_HWTHREAD_REQ(r13) in the system    */
+        /* reset interrupt vector in exceptions-64s.S.        */
+        /* The reason is that another thread can switch the   */
+        /* MMU to a guest context whenever this flag is set   */
+        /* to KVM_HWTHREAD_IN_IDLE, and if the MMU was on,    */
+        /* that would potentially cause this thread to start  */
+        /* executing instructions from guest memory in        */
+        /* hypervisor mode, leading to a host crash or data   */
+        /* corruption, or worse.                              */
+        /******************************************************/
+        stb     r4,HSTATE_HWTHREAD_STATE(r13)
+#endif
         stb     r3,PACA_THREAD_IDLE_STATE(r13)
         cmpwi   cr3,r3,PNV_THREAD_SLEEP
         bge     cr3,2f
@@ -250,6 +264,12 @@ enter_winkle:
  * r3 - requested stop state
  */
 power_enter_stop:
+#ifdef CONFIG_KVM_BOOK3S_HV_POSSIBLE
+        /* Tell KVM we're entering idle */
+        li      r4,KVM_HWTHREAD_IN_IDLE
+        /* DO THIS IN REAL MODE!  See comment above. */
+        stb     r4,HSTATE_HWTHREAD_STATE(r13)
+#endif
 /*
  * Check if the requested state is a deep idle state.
  */