Patch "ARC: Incorrect mm reference used in vmalloc fault handler" has been added to the 3.11-stable tree

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

    ARC: Incorrect mm reference used in vmalloc fault handler

to the 3.11-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:
     arc-incorrect-mm-reference-used-in-vmalloc-fault-handler.patch
and it can be found in the queue-3.11 subdirectory.

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


>From 9c41f4eeb9d51f3ece20428d35a3ea32cf3b5622 Mon Sep 17 00:00:00 2001
From: Vineet Gupta <Vineet.Gupta1@xxxxxxxxxxxx>
Date: Sat, 2 Nov 2013 17:47:49 +0530
Subject: ARC: Incorrect mm reference used in vmalloc fault handler

From: Vineet Gupta <Vineet.Gupta1@xxxxxxxxxxxx>

commit 9c41f4eeb9d51f3ece20428d35a3ea32cf3b5622 upstream.

A vmalloc fault needs to sync up PGD/PTE entry from init_mm to current
task's "active_mm".  ARC vmalloc fault handler however was using mm.

A vmalloc fault for non user task context (actually pre-userland, from
init thread's open for /dev/console) caused the handler to deref NULL mm
(for mm->pgd)

The reasons it worked so far is amazing:

1. By default (!SMP), vmalloc fault handler uses a cached value of PGD.
   In SMP that MMU register is repurposed hence need for mm pointer deref.

2. In pre-3.12 SMP kernel, the problem triggering vmalloc didn't exist in
   pre-userland code path - it was introduced with commit 20bafb3d23d108bc
   "n_tty: Move buffers into n_tty_data"

Signed-off-by: Vineet Gupta <vgupta@xxxxxxxxxxxx>
Cc: Gilad Ben-Yossef <gilad@xxxxxxxxxxxxx>
Cc: Noam Camus <noamc@xxxxxxxxxx>
Cc: Peter Hurley <peter@xxxxxxxxxxxxxxxxxx>
Signed-off-by: Linus Torvalds <torvalds@xxxxxxxxxxxxxxxxxxxx>
Signed-off-by: Greg Kroah-Hartman <gregkh@xxxxxxxxxxxxxxxxxxx>

---
 arch/arc/mm/fault.c |    6 +++---
 1 file changed, 3 insertions(+), 3 deletions(-)

--- a/arch/arc/mm/fault.c
+++ b/arch/arc/mm/fault.c
@@ -17,7 +17,7 @@
 #include <asm/pgalloc.h>
 #include <asm/mmu.h>
 
-static int handle_vmalloc_fault(struct mm_struct *mm, unsigned long address)
+static int handle_vmalloc_fault(unsigned long address)
 {
 	/*
 	 * Synchronize this task's top level page-table
@@ -27,7 +27,7 @@ static int handle_vmalloc_fault(struct m
 	pud_t *pud, *pud_k;
 	pmd_t *pmd, *pmd_k;
 
-	pgd = pgd_offset_fast(mm, address);
+	pgd = pgd_offset_fast(current->active_mm, address);
 	pgd_k = pgd_offset_k(address);
 
 	if (!pgd_present(*pgd_k))
@@ -73,7 +73,7 @@ void do_page_fault(struct pt_regs *regs,
 	 * nothing more.
 	 */
 	if (address >= VMALLOC_START && address <= VMALLOC_END) {
-		ret = handle_vmalloc_fault(mm, address);
+		ret = handle_vmalloc_fault(address);
 		if (unlikely(ret))
 			goto bad_area_nosemaphore;
 		else


Patches currently in stable-queue which might be from Vineet.Gupta1@xxxxxxxxxxxx are

queue-3.11/arc-incorrect-mm-reference-used-in-vmalloc-fault-handler.patch
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