Patch "Revert "arm64: mm: set the contiguous bit for kernel mappings where appropriate"" has been added to the 4.10-stable tree

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

Revert "arm64: mm: set the contiguous bit for kernel mappings where appropriate"

to the 4.10-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:
revert-arm64-mm-set-the-contiguous-bit-for-kernel-mappings-where-appropriate.patch
and it can be found in the queue-4.10 subdirectory.

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

From: Mark Rutland <[email protected]>
Date: Thu, 23 Feb 2017 16:22:55 +0000
Subject: Revert "arm64: mm: set the contiguous bit for kernel mappings where appropriate"

From: Mark Rutland <[email protected]>

commit d81bbe6d882461dec4b71dbe2aa85565fcca4187 upstream.

This reverts commit 0bfc445dec9dd8130d22c9f4476eed7598524129.

When we change the permissions of regions mapped using contiguous entries, the architecture requires us to follow a Break-Before-Make strategy, breaking *all* associated entries before we can change any of the following properties from the entries:

- presence of the contiguous bit
- output address
- attributes
- permissiones

Failure to do so can result in a number of problems (e.g. TLB conflict aborts and/or erroneous results from TLB lookups).

See ARM DDI 0487A.k_iss10775, "Misprogramming of the Contiguous bit", page D4-1762.

We do not take this into account when altering the permissions of kernel segments in mark_rodata_ro(), where we change the permissions of live contiguous entires one-by-one, leaving them transiently inconsistent. This has been observed to result in failures on some fast model configurations.

Unfortunately, we cannot follow Break-Before-Make here as we'd have to unmap kernel text and data used to perform the sequence.

For the timebeing, revert commit 0bfc445dec9dd813 so as to avoid issues resulting from this misuse of the contiguous bit.

---
 arch/arm64/mm/mmu.c |   34 ++++------------------------------
 1 file changed, 4 insertions(+), 30 deletions(-)

@@ -108,10 +108,8 @@ static bool pgattr_change_is_safe(u64 ol
 static void alloc_init_pte(pmd_t *pmd, unsigned long addr,
 				  unsigned long end, unsigned long pfn,
 				  pgprot_t prot,
-				  phys_addr_t (*pgtable_alloc)(void),
-				  bool page_mappings_only)
+				  phys_addr_t (*pgtable_alloc)(void))
 {
-	pgprot_t __prot = prot;
 	pte_t *pte;
 
 	BUG_ON(pmd_sect(*pmd));

@@ -129,18 +127,7 @@ static void alloc_init_pte(pmd_t *pmd, u
 	do {
 		pte_t old_pte = *pte;
 
-		/*
-		 * Set the contiguous bit for the subsequent group of PTEs if
-		 * its size and alignment are appropriate.
-		 */
-		if (((addr | PFN_PHYS(pfn)) & ~CONT_PTE_MASK) == 0) {
-			if (end - addr >= CONT_PTE_SIZE && !page_mappings_only)
-				__prot = __pgprot(pgprot_val(prot) | PTE_CONT);
-			else
-				__prot = prot;
-		}
-
-		set_pte(pte, pfn_pte(pfn, __prot));
+		set_pte(pte, pfn_pte(pfn, prot));
 		pfn++;
 
 		/*

@@ -159,7 +146,6 @@ static void alloc_init_pmd(pud_t *pud, u
 				  phys_addr_t (*pgtable_alloc)(void),
 				  bool page_mappings_only)
 {
-	pgprot_t __prot = prot;
 	pmd_t *pmd;
 	unsigned long next;
 

@@ -186,18 +172,7 @@ static void alloc_init_pmd(pud_t *pud, u
 		/* try section mapping first */
 		if (((addr | next | phys) & ~SECTION_MASK) == 0 &&
 		      !page_mappings_only) {
-			/*
-			 * Set the contiguous bit for the subsequent group of
-			 * PMDs if its size and alignment are appropriate.
-			 */
-			if (((addr | phys) & ~CONT_PMD_MASK) == 0) {
-				if (end - addr >= CONT_PMD_SIZE)
-					__prot = __pgprot(pgprot_val(prot) |
-							  PTE_CONT);
-				else
-					__prot = prot;
-			}
-			pmd_set_huge(pmd, phys, __prot);
+			pmd_set_huge(pmd, phys, prot);
 
 			/*
 			 * After the PMD entry has been populated once, we

@@ -207,8 +182,7 @@ static void alloc_init_pmd(pud_t *pud, u
 						      pmd_val(*pmd)));
 		} else {
 			alloc_init_pte(pmd, addr, next, __phys_to_pfn(phys),
-				       prot, pgtable_alloc,
-				       page_mappings_only);
+				       prot, pgtable_alloc);
 
 			BUG_ON(pmd_val(old_pmd) != 0 &&
 			       pmd_val(old_pmd) != pmd_val(*pmd));

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

queue-4.10/arm64-fix-erroneous-__raw_read_system_reg-cases.patch queue-4.10/revert-arm64-mm-set-the-contiguous-bit-for-kernel-mappings-where-appropriate.patch