Patch "powerpc/book3s/mce: Move add_taint() later in virtual mode" has been added to the 4.4-stable tree

Patch "powerpc/book3s/mce: Move add_taint() later in virtual mode" has been added to the 4.4-stable tree

[gregkh]

This is a note to let you know that I've just added the patch titled

    powerpc/book3s/mce: Move add_taint() later in virtual mode

to the 4.4-stable tree which can be found at:
    http://www.kernel.org/git/?p=linux/kernel/git/stable/stable-queue.git;a=summary

The filename of the patch is:
     powerpc-book3s-mce-move-add_taint-later-in-virtual-mode.patch
and it can be found in the queue-4.4 subdirectory.

If you, or anyone else, feels it should not be added to the stable tree,
please let <stable@vger.kernel.org> know about it.


>From d93b0ac01a9ce276ec39644be47001873d3d183c Mon Sep 17 00:00:00 2001
From: Mahesh Salgaonkar <mahesh@linux.vnet.ibm.com>
Date: Tue, 18 Apr 2017 22:08:17 +0530
Subject: powerpc/book3s/mce: Move add_taint() later in virtual mode

From: Mahesh Salgaonkar <mahesh@linux.vnet.ibm.com>

commit d93b0ac01a9ce276ec39644be47001873d3d183c upstream.

machine_check_early() gets called in real mode. The very first time when
add_taint() is called, it prints a warning which ends up calling opal
call (that uses OPAL_CALL wrapper) for writing it to console. If we get a
very first machine check while we are in opal we are doomed. OPAL_CALL
overwrites the PACASAVEDMSR in r13 and in this case when we are done with
MCE handling the original opal call will use this new MSR on it's way
back to opal_return. This usually leads to unexpected behaviour or the
kernel to panic. Instead move the add_taint() call later in the virtual
mode where it is safe to call.

This is broken with current FW level. We got lucky so far for not getting
very first MCE hit while in OPAL. But easily reproducible on Mambo.

Fixes: 27ea2c420cad ("powerpc: Set the correct kernel taint on machine check errors.")
Signed-off-by: Mahesh Salgaonkar <mahesh@linux.vnet.ibm.com>
Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

---
 arch/powerpc/kernel/mce.c   |    2 ++
 arch/powerpc/kernel/traps.c |    4 ++--
 2 files changed, 4 insertions(+), 2 deletions(-)

--- a/arch/powerpc/kernel/mce.c
+++ b/arch/powerpc/kernel/mce.c
@@ -204,6 +204,8 @@ static void machine_check_process_queued
 {
 	int index;
 
+	add_taint(TAINT_MACHINE_CHECK, LOCKDEP_NOW_UNRELIABLE);
+
 	/*
 	 * For now just print it to console.
 	 * TODO: log this error event to FSP or nvram.
--- a/arch/powerpc/kernel/traps.c
+++ b/arch/powerpc/kernel/traps.c
@@ -297,8 +297,6 @@ long machine_check_early(struct pt_regs
 
 	__this_cpu_inc(irq_stat.mce_exceptions);
 
-	add_taint(TAINT_MACHINE_CHECK, LOCKDEP_NOW_UNRELIABLE);
-
 	if (cur_cpu_spec && cur_cpu_spec->machine_check_early)
 		handled = cur_cpu_spec->machine_check_early(regs);
 	return handled;
@@ -704,6 +702,8 @@ void machine_check_exception(struct pt_r
 
 	__this_cpu_inc(irq_stat.mce_exceptions);
 
+	add_taint(TAINT_MACHINE_CHECK, LOCKDEP_NOW_UNRELIABLE);
+
 	/* See if any machine dependent calls. In theory, we would want
 	 * to call the CPU first, and call the ppc_md. one if the CPU
 	 * one returns a positive number. However there is existing code


Patches currently in stable-queue which might be from mahesh@linux.vnet.ibm.com are

queue-4.4/powerpc-book3s-mce-move-add_taint-later-in-virtual-mode.patch