On 04/04/2017 10:29 AM, tip-bot for Kirill A. Shutemov wrote:
Commit-ID: 361b4b58ec4cf123e12a773909c6454dbd5e6dbc
Gitweb: http://git.kernel.org/tip/361b4b58ec4cf123e12a773909c6454dbd5e6dbc
Author: Kirill A. Shutemov <[email protected]>
AuthorDate: Thu, 30 Mar 2017 11:07:26 +0300
Committer: Ingo Molnar <[email protected]>
CommitDate: Tue, 4 Apr 2017 08:22:33 +0200
x86/asm: Remove __VIRTUAL_MASK_SHIFT==47 assert
We don't need the assert anymore, as:
17be0aec74fb ("x86/asm/entry/64: Implement better check for canonical
addresses")
made canonical address checks generic wrt. address width.
Signed-off-by: Kirill A. Shutemov <[email protected]>
Cc: Andrew Morton <[email protected]>
Cc: Andy Lutomirski <[email protected]>
Cc: Andy Lutomirski <[email protected]>
Cc: Borislav Petkov <[email protected]>
Cc: Brian Gerst <[email protected]>
Cc: Dave Hansen <[email protected]>
Cc: Denys Vlasenko <[email protected]>
Cc: H. Peter Anvin <[email protected]>
Cc: Josh Poimboeuf <[email protected]>
Cc: Linus Torvalds <[email protected]>
Cc: Peter Zijlstra <[email protected]>
Cc: Thomas Gleixner <[email protected]>
Cc: [email protected]
Cc: [email protected]
Link:
http://lkml.kernel.org/r/[email protected]
Signed-off-by: Ingo Molnar <[email protected]>
---
arch/x86/entry/entry_64.S | 7 ++-----
1 file changed, 2 insertions(+), 5 deletions(-)
diff --git a/arch/x86/entry/entry_64.S b/arch/x86/entry/entry_64.S
index 044d18e..f07b4ef 100644
--- a/arch/x86/entry/entry_64.S
+++ b/arch/x86/entry/entry_64.S
@@ -265,12 +265,9 @@ 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
The comment above stops being correct: it's not necessary 16 top bits
we sign-extend now. With larger __VIRTUAL_MASK_SHIFT for 5-level translation,
it will become 7 bits (if I do the math right).
*/
- .ifne __VIRTUAL_MASK_SHIFT - 47
- .error "virtual address width changed -- SYSRET checks need update"
- .endif
-
- /* Change top 16 bits to be the sign-extension of 47th bit */
shl $(64 - (__VIRTUAL_MASK_SHIFT+1)), %rcx
sar $(64 - (__VIRTUAL_MASK_SHIFT+1)), %rcx
The bigger problem here would be the future boot-time choice of 4/5-level
page tables: __VIRTUAL_MASK_SHIFT will need to depend on that choice,
but in this location it is preferable to not use any variables
(memory references).
--
vda
