Patch "s390/mm: fix gmap tlb flush issues" has been added to the 4.7-stable tree

Patch "s390/mm: fix gmap tlb flush issues" has been added to the 4.7-stable tree

[gregkh]

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

    s390/mm: fix gmap tlb flush issues

to the 4.7-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:
     s390-mm-fix-gmap-tlb-flush-issues.patch
and it can be found in the queue-4.7 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 f045402984404ddc11016358411e445192919047 Mon Sep 17 00:00:00 2001
From: David Hildenbrand <dahi@linux.vnet.ibm.com>
Date: Thu, 7 Jul 2016 10:44:10 +0200
Subject: s390/mm: fix gmap tlb flush issues

From: David Hildenbrand <dahi@linux.vnet.ibm.com>

commit f045402984404ddc11016358411e445192919047 upstream.

__tlb_flush_asce() should never be used if multiple asce belong to a mm.

As this function changes mm logic determining if local or global tlb
flushes will be neded, we might end up flushing only the gmap asce on all
CPUs and a follow up mm asce flushes will only flush on the local CPU,
although that asce ran on multiple CPUs.

The missing tlb flushes will provoke strange faults in user space and even
low address protections in user space, crashing the kernel.

Fixes: 1b948d6caec4 ("s390/mm,tlb: optimize TLB flushing for zEC12")
Reported-by: Sascha Silbe <silbe@linux.vnet.ibm.com>
Acked-by: Martin Schwidefsky <schwidefsky@de.ibm.com>
Signed-off-by: David Hildenbrand <dahi@linux.vnet.ibm.com>
Signed-off-by: Martin Schwidefsky <schwidefsky@de.ibm.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

---
 arch/s390/include/asm/tlbflush.h |    3 ++-
 arch/s390/mm/gmap.c              |    4 ++--
 2 files changed, 4 insertions(+), 3 deletions(-)

--- a/arch/s390/include/asm/tlbflush.h
+++ b/arch/s390/include/asm/tlbflush.h
@@ -81,7 +81,8 @@ static inline void __tlb_flush_full(stru
 }
 
 /*
- * Flush TLB entries for a specific ASCE on all CPUs.
+ * Flush TLB entries for a specific ASCE on all CPUs. Should never be used
+ * when more than one asce (e.g. gmap) ran on this mm.
  */
 static inline void __tlb_flush_asce(struct mm_struct *mm, unsigned long asce)
 {
--- a/arch/s390/mm/gmap.c
+++ b/arch/s390/mm/gmap.c
@@ -85,7 +85,7 @@ EXPORT_SYMBOL_GPL(gmap_alloc);
 static void gmap_flush_tlb(struct gmap *gmap)
 {
 	if (MACHINE_HAS_IDTE)
-		__tlb_flush_asce(gmap->mm, gmap->asce);
+		__tlb_flush_idte(gmap->asce);
 	else
 		__tlb_flush_global();
 }
@@ -124,7 +124,7 @@ void gmap_free(struct gmap *gmap)
 
 	/* Flush tlb. */
 	if (MACHINE_HAS_IDTE)
-		__tlb_flush_asce(gmap->mm, gmap->asce);
+		__tlb_flush_idte(gmap->asce);
 	else
 		__tlb_flush_global();
 


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

queue-4.7/s390-mm-don-t-drop-errors-in-get_guest_storage_key.patch
queue-4.7/s390-mm-fix-gmap-tlb-flush-issues.patch