[PATCH] x86/asm: Fix comment in return_from_SYSCALL_64

From: Kirill A. Shutemov
Date: Wed Apr 05 2017 - 07:06:15 EST


On x86-64 __VIRTUAL_MASK_SHIFT depends on paging mode now.

Signed-off-by: Kirill A. Shutemov <kirill.shutemov@xxxxxxxxxxxxxxx>
---
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 607d72c4a485..c70e064d9592 100644
--- a/arch/x86/entry/entry_64.S
+++ b/arch/x86/entry/entry_64.S
@@ -266,7 +266,8 @@ 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 valuable bit (47 or 56
+ * depending on paging mode) in the address.
*/
shl $(64 - (__VIRTUAL_MASK_SHIFT+1)), %rcx
sar $(64 - (__VIRTUAL_MASK_SHIFT+1)), %rcx
--
Kirill A. Shutemov