x86: PAT fix

Adrian Bunk noticed the following Coverity report:

> Commit e7f260a2
> (x86: PAT use reserve free memtype in mmap of /dev/mem)
> added the following gem to arch/x86/mm/pat.c:
>
> <--  snip  -->
>
> ...
> int phys_mem_access_prot_allowed(struct file *file, unsigned long pfn,
>                                 unsigned long size, pgprot_t *vma_prot)
> {
>         u64 offset = ((u64) pfn) << PAGE_SHIFT;
>         unsigned long flags = _PAGE_CACHE_UC_MINUS;
>         unsigned long ret_flags;
> ...
> ...  (nothing that touches ret_flags)
> ...
>         if (flags != _PAGE_CACHE_UC_MINUS) {
>                 retval = reserve_memtype(offset, offset + size, flags, NULL);
>         } else {
>                 retval = reserve_memtype(offset, offset + size, -1, &ret_flags);
>         }
>
>         if (retval < 0)
>                 return 0;
>
>         flags = ret_flags;
>
>         if (pfn <= max_pfn_mapped &&
>             ioremap_change_attr((unsigned long)__va(offset), size, flags) < 0) {
>                 free_memtype(offset, offset + size);
>                 printk(KERN_INFO
>                 "%s:%d /dev/mem ioremap_change_attr failed %s for %Lx-%Lx\n",
>                         current->comm, current->pid,
>                         cattr_name(flags),
>                         offset, offset + size);
>                 return 0;
>         }
>
>         *vma_prot = __pgprot((pgprot_val(*vma_prot) & ~_PAGE_CACHE_MASK) |
>                              flags);
>         return 1;
> }
>
> <--  snip  -->
>
> If (flags != _PAGE_CACHE_UC_MINUS) we pass garbage from the stack to
> ioremap_change_attr() and/or __pgprot().
>
> Spotted by the Coverity checker.

the fix simplifies the code as we get rid of the 'ret_flags'
complication.
Signed-off-by: Ingo Molnar <mingo@elte.hu>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

arch/x86/mm/pat.c

@@ -510,7 +510,6 @@ int phys_mem_access_prot_allowed(struct file *file, unsigned long pfn,
 {
 	u64 offset = ((u64) pfn) << PAGE_SHIFT;
 	unsigned long flags = _PAGE_CACHE_UC_MINUS;
-	unsigned long ret_flags;
 	int retval;
 
 	if (!range_is_allowed(pfn, size))
@@ -549,14 +548,12 @@ int phys_mem_access_prot_allowed(struct file *file, unsigned long pfn,
 	if (flags != _PAGE_CACHE_UC_MINUS) {
 		retval = reserve_memtype(offset, offset + size, flags, NULL);
 	} else {
-		retval = reserve_memtype(offset, offset + size, -1, &ret_flags);
+		retval = reserve_memtype(offset, offset + size, -1, &flags);
 	}
 
 	if (retval < 0)
 		return 0;
 
-	flags = ret_flags;
-
 	if (pfn <= max_pfn_mapped &&
             ioremap_change_attr((unsigned long)__va(offset), size, flags) < 0) {
 		free_memtype(offset, offset + size);