[tip:x86/mm] x86/asm: Fix comment in return_from_SYSCALL_64()

[tip-bot for Kirill A. Shutemov]

Commit-ID:  cbe0317bf10acf1f41811108ed0f9a316103c0f3
Gitweb:     http://git.kernel.org/tip/cbe0317bf10acf1f41811108ed0f9a316103c0f3
Author:     Kirill A. Shutemov <kirill.shutemov@xxxxxxxxxxxxxxx>
AuthorDate: Tue, 6 Jun 2017 14:31:21 +0300
Committer:  Ingo Molnar <mingo@xxxxxxxxxx>
CommitDate: Tue, 13 Jun 2017 08:56:51 +0200

x86/asm: Fix comment in return_from_SYSCALL_64()

On x86-64 __VIRTUAL_MASK_SHIFT depends on paging mode now.

Signed-off-by: Kirill A. Shutemov <kirill.shutemov@xxxxxxxxxxxxxxx>
Cc: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>
Cc: Andy Lutomirski <luto@xxxxxxxxxxxxxx>
Cc: Andy Lutomirski <luto@xxxxxxxxxx>
Cc: Borislav Petkov <bp@xxxxxxxxx>
Cc: Brian Gerst <brgerst@xxxxxxxxx>
Cc: Dave Hansen <dave.hansen@xxxxxxxxx>
Cc: Denys Vlasenko <dvlasenk@xxxxxxxxxx>
Cc: H. Peter Anvin <hpa@xxxxxxxxx>
Cc: Josh Poimboeuf <jpoimboe@xxxxxxxxxx>
Cc: Linus Torvalds <torvalds@xxxxxxxxxxxxxxxxxxxx>
Cc: Peter Zijlstra <peterz@xxxxxxxxxxxxx>
Cc: Thomas Gleixner <tglx@xxxxxxxxxxxxx>
Cc: linux-arch@xxxxxxxxxxxxxxx
Cc: linux-mm@xxxxxxxxx
Link: http://lkml.kernel.org/r/20170606113133.22974-3-kirill.shutemov@xxxxxxxxxxxxxxx
Signed-off-by: Ingo Molnar <mingo@xxxxxxxxxx>
---
 arch/x86/entry/entry_64.S | 3 ++-
 1 file changed, 2 insertions(+), 1 deletion(-)

diff --git a/arch/x86/entry/entry_64.S b/arch/x86/entry/entry_64.S
index 4a4c083..a9a8027 100644
--- a/arch/x86/entry/entry_64.S
+++ b/arch/x86/entry/entry_64.S
@@ -265,7 +265,8 @@ return_from_SYSCALL_64:
 	 * If width of "canonical tail" ever becomes variable, this will need
 	 * to be updated to remain correct on both old and new CPUs.
 	 *
-	 * Change top 16 bits to be the sign-extension of 47th bit
+	 * Change top bits to match most significant bit (47th or 56th bit
+	 * depending on paging mode) in the address.
 	 */
 	shl	$(64 - (__VIRTUAL_MASK_SHIFT+1)), %rcx
 	sar	$(64 - (__VIRTUAL_MASK_SHIFT+1)), %rcx