Patch "x86/mm/pat: Fix BUG_ON() in mmap_mem() on QEMU/i386" has been added to the 4.6-stable tree

[<gregkh@linuxfoundation.org>]

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

    x86/mm/pat: Fix BUG_ON() in mmap_mem() on QEMU/i386

to the 4.6-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:
     x86-mm-pat-fix-bug_on-in-mmap_mem-on-qemu-i386.patch
and it can be found in the queue-4.6 subdirectory.

If you, or anyone else, feels it should not be added to the stable tree,
please let <stable@vger.kernel.org> know about it.


>From 1886297ce0c8d563a08c8a8c4c0b97743e06cd37 Mon Sep 17 00:00:00 2001
From: Toshi Kani <toshi.kani@hpe.com>
Date: Mon, 11 Apr 2016 13:36:00 -0600
Subject: x86/mm/pat: Fix BUG_ON() in mmap_mem() on QEMU/i386

From: Toshi Kani <toshi.kani@hpe.com>

commit 1886297ce0c8d563a08c8a8c4c0b97743e06cd37 upstream.

The following BUG_ON() crash was reported on QEMU/i386:

  kernel BUG at arch/x86/mm/physaddr.c:79!
  Call Trace:
  phys_mem_access_prot_allowed
  mmap_mem
  ? mmap_region
  mmap_region
  do_mmap
  vm_mmap_pgoff
  SyS_mmap_pgoff
  do_int80_syscall_32
  entry_INT80_32

after commit:

  edfe63ec97ed ("x86/mtrr: Fix Xorg crashes in Qemu sessions")

PAT is now set to disabled state when MTRRs are disabled.
Thus, reactivating the __pa(high_memory) check in
phys_mem_access_prot_allowed().

When CONFIG_DEBUG_VIRTUAL is set, __pa() calls __phys_addr(),
which in turn calls slow_virt_to_phys() for 'high_memory'.
Because 'high_memory' is set to (the max direct mapped virt
addr + 1), it is not a valid virtual address.  Hence,
slow_virt_to_phys() returns 0 and hit the BUG_ON.  Using
__pa_nodebug() instead of __pa() will fix this BUG_ON.

However, this code block, originally written for Pentiums and
earlier, is no longer adequate since a 32-bit Xen guest has
MTRRs disabled and supports ZONE_HIGHMEM.  In this setup,
this code sets UC attribute for accessing RAM in high memory
range.

Delete this code block as it has been unused for a long time.

Reported-by: kernel test robot <ying.huang@linux.intel.com>
Reviewed-by: Borislav Petkov <bp@suse.de>
Signed-off-by: Toshi Kani <toshi.kani@hpe.com>
Cc: Andrew Morton <akpm@linux-foundation.org>
Cc: David Vrabel <david.vrabel@citrix.com>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: xen-devel@lists.xenproject.org
Link: http://lkml.kernel.org/r/1460403360-25441-1-git-send-email-toshi.kani@hpe.com
Link: https://lkml.org/lkml/2016/4/1/608
Signed-off-by: Ingo Molnar <mingo@kernel.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

---
 arch/x86/mm/pat.c |   19 -------------------
 1 file changed, 19 deletions(-)

--- a/arch/x86/mm/pat.c
+++ b/arch/x86/mm/pat.c
@@ -778,25 +778,6 @@ int phys_mem_access_prot_allowed(struct
 	if (file->f_flags & O_DSYNC)
 		pcm = _PAGE_CACHE_MODE_UC_MINUS;
 
-#ifdef CONFIG_X86_32
-	/*
-	 * On the PPro and successors, the MTRRs are used to set
-	 * memory types for physical addresses outside main memory,
-	 * so blindly setting UC or PWT on those pages is wrong.
-	 * For Pentiums and earlier, the surround logic should disable
-	 * caching for the high addresses through the KEN pin, but
-	 * we maintain the tradition of paranoia in this code.
-	 */
-	if (!pat_enabled() &&
-	    !(boot_cpu_has(X86_FEATURE_MTRR) ||
-	      boot_cpu_has(X86_FEATURE_K6_MTRR) ||
-	      boot_cpu_has(X86_FEATURE_CYRIX_ARR) ||
-	      boot_cpu_has(X86_FEATURE_CENTAUR_MCR)) &&
-	    (pfn << PAGE_SHIFT) >= __pa(high_memory)) {
-		pcm = _PAGE_CACHE_MODE_UC;
-	}
-#endif
-
 	*vma_prot = __pgprot((pgprot_val(*vma_prot) & ~_PAGE_CACHE_MASK) |
 			     cachemode2protval(pcm));
 	return 1;


Patches currently in stable-queue which might be from toshi.kani@hpe.com are

queue-4.6/x86-mm-pat-replace-cpu_has_pat-with-boot_cpu_has.patch
queue-4.6/x86-mtrr-fix-xorg-crashes-in-qemu-sessions.patch
queue-4.6/libnvdimm-pfn-dax-fix-initialization-vs-autodetect-for-mode-alignment.patch
queue-4.6/x86-mm-pat-add-support-of-non-default-pat-msr-setting.patch
queue-4.6/x86-xen-pat-remove-pat-table-init-code-from-xen.patch
queue-4.6/x86-mtrr-fix-pat-init-handling-when-mtrr-is-disabled.patch
queue-4.6/x86-mm-pat-add-pat_disable-interface.patch
queue-4.6/x86-mm-pat-fix-bug_on-in-mmap_mem-on-qemu-i386.patch
queue-4.6/x86-pat-document-the-pat-initialization-sequence.patch