[3.13.y.z extended stable] Patch "sparc64: Do not insert non-valid PTEs into the TSB hash table." has been added to staging queue

[Kamal Mostafa]

This is a note to let you know that I have just added a patch titled

    sparc64: Do not insert non-valid PTEs into the TSB hash table.

to the linux-3.13.y-queue branch of the 3.13.y.z extended stable tree 
which can be found at:

 http://kernel.ubuntu.com/git?p=ubuntu/linux.git;a=shortlog;h=refs/heads/linux-3.13.y-queue

This patch is scheduled to be released in version 3.13.11.7.

If you, or anyone else, feels it should not be added to this tree, please 
reply to this email.

For more information about the 3.13.y.z tree, see
https://wiki.ubuntu.com/Kernel/Dev/ExtendedStable

Thanks.
-Kamal

------

>From 802dbaffe8a222ad4f5be9ba7329781c16c6d9a1 Mon Sep 17 00:00:00 2001
From: "David S. Miller" <davem at davemloft.net>
Date: Mon, 4 Aug 2014 16:34:01 -0700
Subject: sparc64: Do not insert non-valid PTEs into the TSB hash table.

[ Upstream commit 18f38132528c3e603c66ea464727b29e9bbcb91b ]

The assumption was that update_mmu_cache() (and the equivalent for PMDs) would
only be called when the PTE being installed will be accessible by the user.

This is not true for code paths originating from remove_migration_pte().

There are dire consequences for placing a non-valid PTE into the TSB.  The TLB
miss frramework assumes thatwhen a TSB entry matches we can just load it into
the TLB and return from the TLB miss trap.

So if a non-valid PTE is in there, we will deadlock taking the TLB miss over
and over, never satisfying the miss.

Just exit early from update_mmu_cache() and friends in this situation.

Based upon a report and patch from Christopher Alexander Tobias Schulze.

Signed-off-by: David S. Miller <davem at davemloft.net>
Signed-off-by: Kamal Mostafa <kamal at canonical.com>
---
 arch/sparc/mm/init_64.c | 8 ++++++++
 1 file changed, 8 insertions(+)

diff --git a/arch/sparc/mm/init_64.c b/arch/sparc/mm/init_64.c
index 848bea7..16b61aa 100644
--- a/arch/sparc/mm/init_64.c
+++ b/arch/sparc/mm/init_64.c
@@ -350,6 +350,10 @@ void update_mmu_cache(struct vm_area_struct *vma, unsigned long address, pte_t *

 	mm = vma->vm_mm;

+	/* Don't insert a non-valid PTE into the TSB, we'll deadlock.  */
+	if (!pte_accessible(mm, pte))
+		return;
+
 	spin_lock_irqsave(&mm->context.lock, flags);

 #if defined(CONFIG_HUGETLB_PAGE) || defined(CONFIG_TRANSPARENT_HUGEPAGE)
@@ -2613,6 +2617,10 @@ void update_mmu_cache_pmd(struct vm_area_struct *vma, unsigned long addr,

 	pte = pmd_val(entry);

+	/* Don't insert a non-valid PMD into the TSB, we'll deadlock.  */
+	if (!(pte & _PAGE_VALID))
+		return;
+
 	/* We are fabricating 8MB pages using 4MB real hw pages.  */
 	pte |= (addr & (1UL << REAL_HPAGE_SHIFT));

--
1.9.1