[PATCH] x86_64: clobber flags in clear_page()

[PATCH] x86_64: clobber flags in clear_page()

[Alexey Dobriyan]

All clear_page() implementations use XOR which resets flags.

Judging by allyesconfig disassembly no code is affected.

Signed-off-by: Alexey Dobriyan <adobriyan@gmail.com>
---

 arch/x86/include/asm/page_64.h |    2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

--- a/arch/x86/include/asm/page_64.h
+++ b/arch/x86/include/asm/page_64.h
@@ -47,7 +47,7 @@ static inline void clear_page(void *page)
 			   clear_page_erms, X86_FEATURE_ERMS,
 			   "=D" (page),
 			   "0" (page)
-			   : "memory", "rax", "rcx");
+			   : "cc", "memory", "rax", "rcx");
 }
 
 void copy_page(void *to, void *from);

Re: [PATCH] x86_64: clobber flags in clear_page()

[Borislav Petkov]

On Sat, Jan 13, 2018 at 09:50:48PM +0300, Alexey Dobriyan wrote:
> All clear_page() implementations use XOR which resets flags.
> 
> Judging by allyesconfig disassembly no code is affected.
> 
> Signed-off-by: Alexey Dobriyan <adobriyan@gmail.com>
> ---
> 
>  arch/x86/include/asm/page_64.h |    2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
> 
> --- a/arch/x86/include/asm/page_64.h
> +++ b/arch/x86/include/asm/page_64.h
> @@ -47,7 +47,7 @@ static inline void clear_page(void *page)
>  			   clear_page_erms, X86_FEATURE_ERMS,
>  			   "=D" (page),
>  			   "0" (page)
> -			   : "memory", "rax", "rcx");
> +			   : "cc", "memory", "rax", "rcx");
>  }
>  
>  void copy_page(void *to, void *from);

Reviewed-by: Borislav Petkov <bp@suse.de>

-- 
Regards/Gruss,
    Boris.

SUSE Linux GmbH, GF: Felix Imendörffer, Jane Smithard, Graham Norton, HRB 21284 (AG Nürnberg)
-- 

[tip:x86/asm] x86/asm: Clobber flags in clear_page()

[tip-bot for Alexey Dobriyan]

Commit-ID:  1acdbf7ea8a80706561013346d281d282a3c00f9
Gitweb:     https://git.kernel.org/tip/1acdbf7ea8a80706561013346d281d282a3c00f9
Author:     Alexey Dobriyan <adobriyan@gmail.com>
AuthorDate: Sat, 13 Jan 2018 21:50:48 +0300
Committer:  Ingo Molnar <mingo@kernel.org>
CommitDate: Tue, 13 Feb 2018 17:36:49 +0100

x86/asm: Clobber flags in clear_page()

All clear_page() implementations use XOR which resets flags.

Judging by allyesconfig disassembly no code is affected.

Signed-off-by: Alexey Dobriyan <adobriyan@gmail.com>
Reviewed-by: Borislav Petkov <bp@suse.de>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Thomas Gleixner <tglx@linutronix.de>
Link: http://lkml.kernel.org/r/20180113185048.GA23111@avx2
Signed-off-by: Ingo Molnar <mingo@kernel.org>
---
 arch/x86/include/asm/page_64.h | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/arch/x86/include/asm/page_64.h b/arch/x86/include/asm/page_64.h
index 4baa6bc..f8a85c6 100644
--- a/arch/x86/include/asm/page_64.h
+++ b/arch/x86/include/asm/page_64.h
@@ -47,7 +47,7 @@ static inline void clear_page(void *page)
 			   clear_page_erms, X86_FEATURE_ERMS,
 			   "=D" (page),
 			   "0" (page)
-			   : "memory", "rax", "rcx");
+			   : "cc", "memory", "rax", "rcx");
 }
 
 void copy_page(void *to, void *from);