[PATCH v6 17/41] mm: Move VM_UFFD_MINOR_BIT from 37 to 38

[Rick Edgecombe]

From: Yu-cheng Yu <yu-cheng.yu@xxxxxxxxx>

The x86 Control-flow Enforcement Technology (CET) feature includes a new
type of memory called shadow stack. This shadow stack memory has some
unusual properties, which requires some core mm changes to function
properly.

Future patches will introduce a new VM flag VM_SHADOW_STACK that will be
VM_HIGH_ARCH_BIT_5. VM_HIGH_ARCH_BIT_1 through VM_HIGH_ARCH_BIT_4 are
bits 32-36, and bit 37 is the unrelated VM_UFFD_MINOR_BIT. For the sake
of order, make all VM_HIGH_ARCH_BITs stay together by moving
VM_UFFD_MINOR_BIT from 37 to 38. This will allow VM_SHADOW_STACK to be
introduced as 37.

Tested-by: Pengfei Xu <pengfei.xu@xxxxxxxxx>
Tested-by: John Allen <john.allen@xxxxxxx>
Reviewed-by: Kees Cook <keescook@xxxxxxxxxxxx>
Acked-by: Peter Xu <peterx@xxxxxxxxxx>
Signed-off-by: Yu-cheng Yu <yu-cheng.yu@xxxxxxxxx>
Reviewed-by: Axel Rasmussen <axelrasmussen@xxxxxxxxxx>
Signed-off-by: Rick Edgecombe <rick.p.edgecombe@xxxxxxxxx>
Cc: Peter Xu <peterx@xxxxxxxxxx>
Cc: Mike Kravetz <mike.kravetz@xxxxxxxxxx>
---
 include/linux/mm.h | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/include/linux/mm.h b/include/linux/mm.h
index 4650e2580d60..e6f1789c8e69 100644
--- a/include/linux/mm.h
+++ b/include/linux/mm.h
@@ -366,7 +366,7 @@ extern unsigned int kobjsize(const void *objp);
 #endif
 
 #ifdef CONFIG_HAVE_ARCH_USERFAULTFD_MINOR
-# define VM_UFFD_MINOR_BIT	37
+# define VM_UFFD_MINOR_BIT	38
 # define VM_UFFD_MINOR		BIT(VM_UFFD_MINOR_BIT)	/* UFFD minor faults */
 #else /* !CONFIG_HAVE_ARCH_USERFAULTFD_MINOR */
 # define VM_UFFD_MINOR		VM_NONE
-- 
2.17.1