Patch "parisc: Purge TLB before setting PTE" has been added to the 4.4-stable tree

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

parisc: Purge TLB before setting PTE

to the 4.4-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:
parisc-purge-tlb-before-setting-pte.patch
and it can be found in the queue-4.4 subdirectory.

If you, or anyone else, feels it should not be added to the stable tree, please let <[email protected]> know about it.

From: John David Anglin <[email protected]>
Date: Tue, 6 Dec 2016 21:47:04 -0500
Subject: parisc: Purge TLB before setting PTE

From: John David Anglin <[email protected]>

commit c78e710c1c9fbeff43dddc0aa3d0ff458e70b0cc upstream.

The attached change interchanges the order of purging the TLB and setting the corresponding page table entry. TLB purges are strongly ordered. It occurred to me one night that setting the PTE first might have subtle ordering issues on SMP machines and cause random memory corruption.

A TLB lock guards the insertion of user TLB entries. So after the TLB is purged, a new entry can't be inserted until the lock is released. This ensures that the new PTE value is used when the lock is released.

Since making this change, no random segmentation faults have been observed on the Debian hppa buildd servers.

---
 arch/parisc/include/asm/pgtable.h |    8 ++++----
 1 file changed, 4 insertions(+), 4 deletions(-)

@@ -65,9 +65,9 @@ static inline void purge_tlb_entries(str
 		unsigned long flags;				\
 		spin_lock_irqsave(&pa_tlb_lock, flags);		\
 		old_pte = *ptep;				\
-		set_pte(ptep, pteval);				\
 		if (pte_inserted(old_pte))			\
 			purge_tlb_entries(mm, addr);		\
+		set_pte(ptep, pteval);				\
 		spin_unlock_irqrestore(&pa_tlb_lock, flags);	\
 	} while (0)
 

@@ -478,8 +478,8 @@ static inline int ptep_test_and_clear_yo
 		spin_unlock_irqrestore(&pa_tlb_lock, flags);
 		return 0;
 	}
-	set_pte(ptep, pte_mkold(pte));
 	purge_tlb_entries(vma->vm_mm, addr);
+	set_pte(ptep, pte_mkold(pte));
 	spin_unlock_irqrestore(&pa_tlb_lock, flags);
 	return 1;
 }

@@ -492,9 +492,9 @@ static inline pte_t ptep_get_and_clear(s
 
 	spin_lock_irqsave(&pa_tlb_lock, flags);
 	old_pte = *ptep;
-	set_pte(ptep, __pte(0));
 	if (pte_inserted(old_pte))
 		purge_tlb_entries(mm, addr);
+	set_pte(ptep, __pte(0));
 	spin_unlock_irqrestore(&pa_tlb_lock, flags);
 
 	return old_pte;

@@ -504,8 +504,8 @@ static inline void ptep_set_wrprotect(st
 {
 	unsigned long flags;
 	spin_lock_irqsave(&pa_tlb_lock, flags);
-	set_pte(ptep, pte_wrprotect(*ptep));
 	purge_tlb_entries(mm, addr);
+	set_pte(ptep, pte_wrprotect(*ptep));
 	spin_unlock_irqrestore(&pa_tlb_lock, flags);
 }
 

Patches currently in stable-queue which might be from [email protected] are

queue-4.4/parisc-remove-unnecessary-tlb-purges-from-flush_dcache_page_asm-and-flush_icache_page_asm.patch queue-4.4/parisc-purge-tlb-before-setting-pte.patch