1 files changed, 17 insertions, 3 deletions

diff --git a/arch/powerpc/kernel/idle_book3s.S b/arch/powerpc/kernel/idle_book3s.S
index 72dac0b58061..b350ac5e3111 100644
--- a/arch/powerpc/kernel/idle_book3s.S
+++ b/arch/powerpc/kernel/idle_book3s.S
@@ -439,9 +439,23 @@ END_FTR_SECTION_IFSET(CPU_FTR_ARCH_300)
 _GLOBAL(pnv_wakeup_tb_loss)
         ld      r1,PACAR1(r13)
         /*
-         * Before entering any idle state, the NVGPRs are saved in the stack
-         * and they are restored before switching to the process context. Hence
-         * until they are restored, they are free to be used.
+         * Before entering any idle state, the NVGPRs are saved in the stack.
+         * If there was a state loss, or PACA_NAPSTATELOST was set, then the
+         * NVGPRs are restored. If we are here, it is likely that state is lost,
+         * but not guaranteed -- neither ISA207 nor ISA300 tests to reach
+         * here are the same as the test to restore NVGPRS:
+         * PACA_THREAD_IDLE_STATE test for ISA207, PSSCR test for ISA300,
+         * and SRR1 test for restoring NVGPRs.
+         *
+         * We are about to clobber NVGPRs now, so set NAPSTATELOST to
+         * guarantee they will always be restored. This might be tightened
+         * with careful reading of specs (particularly for ISA300) but this
+         * is already a slow wakeup path and it's simpler to be safe.
+         */
+        li      r0,1
+        stb     r0,PACA_NAPSTATELOST(r13)
+
+        /*
          *
          * Save SRR1 and LR in NVGPRs as they might be clobbered in
          * opal_call() (called in CHECK_HMI_INTERRUPT). SRR1 is required