powerpc/pseries/mce: restore msr before returning from handler

The pseries real-mode machine check handler can enable the MMU, and
return from the handler with the MMU still enabled.

This works, but real-mode handler wrapper exit handlers want to rely
on the MMU being in real-mode. So change the pseries handler to
restore the MSR after it has finished virtual mode tasks.

Signed-off-by: Nicholas Piggin <npiggin@gmail.com>
Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>
Link: https://lore.kernel.org/r/1612702361.lm7fqo56re.astroid@bobo.none

diff --git a/arch/powerpc/platforms/pseries/ras.c b/arch/powerpc/platforms/pseries/ras.c
index 92c08fe..f8b390a 100644 (file)
--- a/arch/powerpc/platforms/pseries/ras.c
+++ b/arch/powerpc/platforms/pseries/ras.c
@@ -717,6 +717,7 @@ static int mce_handle_error(struct pt_regs *regs, struct rtas_error_log *errp)
        struct pseries_errorlog *pseries_log;
        struct pseries_mc_errorlog *mce_log = NULL;
        int disposition = rtas_error_disposition(errp);
+       unsigned long msr;
        u8 error_type;
 
        if (!rtas_error_extended(errp))
@@ -742,9 +743,21 @@ static int mce_handle_error(struct pt_regs *regs, struct rtas_error_log *errp)
         *       SLB multihit is done by now.
         */
 out:
-       mtmsr(mfmsr() | MSR_IR | MSR_DR);
+       msr = mfmsr();
+       mtmsr(msr | MSR_IR | MSR_DR);
+
        disposition = mce_handle_err_virtmode(regs, errp, mce_log,
                                              disposition);
+
+       /*
+        * Queue irq work to log this rtas event later.
+        * irq_work_queue uses per-cpu variables, so do this in virt
+        * mode as well.
+        */
+       irq_work_queue(&mce_errlog_process_work);
+
+       mtmsr(msr);
+
        return disposition;
 }
 
@@ -860,10 +873,8 @@ long pseries_machine_check_realmode(struct pt_regs *regs)
                 * virtual mode.
                 */
                disposition = mce_handle_error(regs, errp);
-               fwnmi_release_errinfo();
 
-               /* Queue irq work to log this rtas event later. */
-               irq_work_queue(&mce_errlog_process_work);
+               fwnmi_release_errinfo();
 
                if (disposition == RTAS_DISP_FULLY_RECOVERED)
                        return 1;