[PATCH 3.13 029/187] sparc64: Do not insert non-valid PTEs into the TSB hash table.

Kamal Mostafa
2014-09-15T22:39:27Z

From: "David S. Miller" <davem@davemloft.net>

[ 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@davemloft.net>
Signed-off-by: Kamal Mostafa <kamal@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