[PATCH 3/5] avoid /dev/kmem oopses with DEBUG_VIRTUAL

[Dave Hansen <dave@sr71.net>]

DEBUG_VIRTUAL, ensures that when __pa() is only called on
addresses for which its results are correct.  For everything
else, we BUG_ON().

This changes the /dev/kmem ordering so that we check pfn_valid()
_before_ we call __pa().  This ensures we're not calling __pa()
with gibberish and avoids the BUG_ON() in those cases, instead
returning the error to userspace _before_ the __pa() call.



Signed-off-by: Dave Hansen <dave.hansen@linux.intel.com>
---

 linux.git-davehans/drivers/char/mem.c |    6 +++---
 1 file changed, 3 insertions(+), 3 deletions(-)

diff -puN drivers/char/mem.c~make-devmem-work-on-highmem3a drivers/char/mem.c
--- linux.git/drivers/char/mem.c~make-devmem-work-on-highmem3a	2013-04-10 16:23:45.361087291 -0700
+++ linux.git-davehans/drivers/char/mem.c	2013-04-10 16:23:45.365087295 -0700
@@ -347,9 +347,6 @@ static int mmap_kmem(struct file *file,
 	 */
 	if (kernel_vaddr >= high_memory)
 		return -EIO;
-	/* Turn a kernel-virtual address into a physical page frame */
-	pfn = __pa(kernel_vaddr) >> PAGE_SHIFT;
-
 	/*
 	 * RED-PEN: on some architectures there is more mapped memory than
 	 * available in mem_map which pfn_valid checks for. Perhaps should add a
@@ -360,6 +357,9 @@ static int mmap_kmem(struct file *file,
 	if (!pfn_valid(pfn))
 		return -EIO;
 
+	/* Turn a kernel-virtual address into a physical page frame */
+	pfn = __pa(kernel_vaddr) >> PAGE_SHIFT;
+
 	vma->vm_pgoff = pfn;
 	return mmap_mem(file, vma);
 }
_