Commit-ID: 1886297ce0c8d563a08c8a8c4c0b97743e06cd37
Gitweb: http://git.kernel.org/tip/1886297ce0c8d563a08c8a8c4c0b97743e06cd37
Author: Toshi Kani <toshi.k...@hpe.com>
AuthorDate: Mon, 11 Apr 2016 13:36:00 -0600
Committer: Ingo Molnar <mi...@kernel.org>
CommitDate: Wed, 13 Apr 2016 11:35:33 +0200
x86/mm/pat: Fix BUG_ON() in mmap_mem() on QEMU/i386
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.hu...@linux.intel.com>
Reviewed-by: Borislav Petkov <b...@suse.de>
Signed-off-by: Toshi Kani <toshi.k...@hpe.com>
Cc: Andrew Morton <a...@linux-foundation.org>
Cc: David Vrabel <david.vra...@citrix.com>
Cc: Linus Torvalds <torva...@linux-foundation.org>
Cc: Paul E. McKenney <paul...@linux.vnet.ibm.com>
Cc: Peter Zijlstra <pet...@infradead.org>
Cc: Thomas Gleixner <t...@linutronix.de>
Cc: xen-de...@lists.xenproject.org
Link:
http://lkml.kernel.org/r/1460403360-25441-1-git-send-email-toshi.k...@hpe.com
Link: https://lkml.org/lkml/2016/4/1/608
Signed-off-by: Ingo Molnar <mi...@kernel.org>
---
arch/x86/mm/pat.c | 19 -------------------
1 file changed, 19 deletions(-)
diff --git a/arch/x86/mm/pat.c b/arch/x86/mm/pat.c
index c4c3ddc..fb0604f 100644
--- a/arch/x86/mm/pat.c
+++ b/arch/x86/mm/pat.c
@@ -778,25 +778,6 @@ int phys_mem_access_prot_allowed(struct file *file,
unsigned long pfn,
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;
