linux-kernel - [PATCH 3.2 115/131] sparc64: Do not insert non-valid PTEs into the TSB hash table.

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Message-ID: <lsq.1410438733.290741435@decadent.org.uk>
Date:	Thu, 11 Sep 2014 13:32:13 +0100
From:	Ben Hutchings <ben@...adent.org.uk>
To:	linux-kernel@...r.kernel.org, stable@...r.kernel.org
CC:	akpm@...ux-foundation.org, "David S. Miller" <davem@...emloft.net>
Subject: [PATCH 3.2 115/131] sparc64: Do not insert non-valid PTEs into
 the TSB hash  table.

3.2.63-rc1 review patch.  If anyone has any objections, please let me know.

------------------

From: "David S. Miller" <davem@...emloft.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@...emloft.net>
Signed-off-by: Ben Hutchings <ben@...adent.org.uk>
---
 arch/sparc/mm/init_64.c | 4 ++++
 1 file changed, 4 insertions(+)

diff --git a/arch/sparc/mm/init_64.c b/arch/sparc/mm/init_64.c
index b4989f9..77ad815 100644
--- a/arch/sparc/mm/init_64.c
+++ b/arch/sparc/mm/init_64.c
@@ -309,6 +309,10 @@ void update_mmu_cache(struct vm_area_struct *vma, unsigned long address, pte_t *
 	tsb_index = MM_TSB_BASE;
 	tsb_hash_shift = PAGE_SHIFT;

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

 #ifdef CONFIG_HUGETLB_PAGE

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