mm: Move VM_UFFD_MINOR_BIT from 37 to 38

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.

Co-developed-by: Rick Edgecombe <rick.p.edgecombe@intel.com>
Signed-off-by: Yu-cheng Yu <yu-cheng.yu@intel.com>
Signed-off-by: Rick Edgecombe <rick.p.edgecombe@intel.com>
Signed-off-by: Dave Hansen <dave.hansen@linux.intel.com>
Reviewed-by: Borislav Petkov (AMD) <bp@alien8.de>
Reviewed-by: Kees Cook <keescook@chromium.org>
Reviewed-by: Axel Rasmussen <axelrasmussen@google.com>
Acked-by: Mike Rapoport (IBM) <rppt@kernel.org>
Acked-by: Peter Xu <peterx@redhat.com>
Tested-by: Pengfei Xu <pengfei.xu@intel.com>
Tested-by: John Allen <john.allen@amd.com>
Tested-by: Kees Cook <keescook@chromium.org>
Link: https://lore.kernel.org/all/20230613001108.3040476-6-rick.p.edgecombe%40intel.com

diff --git a/include/linux/mm.h b/include/linux/mm.h
index f9a627c492f29f2de4797b9da8d580fe8a4a5c35..82990f3390f6c07768f062ef7bdd5c5394d84b48 100644 (file)
--- a/include/linux/mm.h
+++ b/include/linux/mm.h
@@ -370,7 +370,7 @@ 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