From: Borislav Petkov <bp@alien8.de>
To: Quentin Casasnovas <quentin.casasnovas@oracle.com>
Cc: X86 ML <x86@kernel.org>, LKML <linux-kernel@vger.kernel.org>,
"H. Peter Anvin" <hpa@zytor.com>, Ingo Molnar <mingo@kernel.org>,
Thomas Gleixner <tglx@linutronix.de>,
Oleg Nesterov <oleg@redhat.com>,
Andy Lutomirski <luto@amacapital.net>
Subject: Re: [PATCH] x86/xsave: Robustify and merge macros
Date: Sat, 4 Apr 2015 11:25:36 +0200 [thread overview]
Message-ID: <20150404092536.GB21152@pd.tnic> (raw)
In-Reply-To: <20150404083611.GA5922@chrystal.uk.oracle.com>
On Sat, Apr 04, 2015 at 10:36:11AM +0200, Quentin Casasnovas wrote:
> Since all of these are compile time constants, could we not use the safe
> variant on that same page? Not that I'm too worried about the signed right
> shift but heh that would be portable and should not impact performance
> anyway, so no added value in using the optimized version is there?
Seems to work with the experimental diff below. I need to do
-(-(x < y))
with the last term though as we're working with s32s.
---
diff --git a/arch/x86/include/asm/alternative-asm.h b/arch/x86/include/asm/alternative-asm.h
index 44a1fc5439d3..2cb6da2716bf 100644
--- a/arch/x86/include/asm/alternative-asm.h
+++ b/arch/x86/include/asm/alternative-asm.h
@@ -53,14 +53,14 @@
* Shamelessly stolen and adapted from:
* http://graphics.stanford.edu/~seander/bithacks.html#IntegerMinOrMax
*/
-#define alt_max_short(a,b) (((a) - (((a) - (b)) & (((a) - (b)) >> 15))) & 0xffff)
+#define alt_max_short(a, b) ((a) ^ (((a) ^ (b)) & -(-((a) < (b)))))
.macro ALTERNATIVE_2 oldinstr, newinstr1, feature1, newinstr2, feature2
140:
\oldinstr
141:
- .skip -((alt_max_short(new_len1, new_len2) - old_len) > 0) * \
- (alt_max_short(new_len1, new_len2) - old_len),0x90
+ .skip -((alt_max_short(new_len1, new_len2) - (old_len)) > 0) * \
+ (alt_max_short(new_len1, new_len2) - (old_len)),0x90
142:
.pushsection .altinstructions,"a"
diff --git a/arch/x86/lib/memset_64.S b/arch/x86/lib/memset_64.S
index 93118fb23976..453b6a05a07e 100644
--- a/arch/x86/lib/memset_64.S
+++ b/arch/x86/lib/memset_64.S
@@ -29,6 +29,14 @@ ENTRY(__memset)
ALTERNATIVE_2 "jmp memset_orig", "", X86_FEATURE_REP_GOOD, \
"jmp memset_erms", X86_FEATURE_ERMS
+ ALTERNATIVE_2 \
+ ".byte 0xc3, 0xc3, 0xc3", \
+ ".byte 0x66, 0x66, 0x66, 0x90", \
+ X86_FEATURE_ALWAYS, \
+ ".byte 0x66, 0x66, 0x66, 0x66, 0xcc", \
+ X86_FEATURE_ALWAYS
+
+
movq %rdi,%r9
movq %rdx,%rcx
andl $7,%edx
> On the bonus side, you're getting rid of the double 'alt_end_marker' label
> in case of an alternative_2()!
>
> Looks good to me and I find it much easier to understand here :)
Cool. Please give it more critical staring as we're under time pressure
here.
Thanks!
--
Regards/Gruss,
Boris.
ECO tip #101: Trim your mails when you reply.
--
next prev parent reply other threads:[~2015-04-04 9:27 UTC|newest]
Thread overview: 22+ messages / expand[flat|nested] mbox.gz Atom feed top
2015-04-02 13:11 [PATCH] x86/xsave: Robustify and merge macros Borislav Petkov
2015-04-02 15:52 ` Quentin Casasnovas
2015-04-02 16:12 ` Borislav Petkov
2015-04-02 16:33 ` Quentin Casasnovas
2015-04-02 16:45 ` Borislav Petkov
2015-04-03 14:06 ` Quentin Casasnovas
2015-04-03 14:14 ` Quentin Casasnovas
2015-04-03 15:23 ` Borislav Petkov
2015-04-03 15:40 ` Quentin Casasnovas
2015-04-03 17:06 ` Borislav Petkov
2015-04-03 17:33 ` Quentin Casasnovas
2015-04-03 17:48 ` Borislav Petkov
2015-04-03 20:42 ` Quentin Casasnovas
2015-04-04 7:34 ` Borislav Petkov
2015-04-04 8:36 ` Quentin Casasnovas
2015-04-04 9:25 ` Borislav Petkov [this message]
2015-04-04 10:11 ` Quentin Casasnovas
2015-04-04 10:29 ` Borislav Petkov
2015-04-04 13:32 ` Borislav Petkov
2015-04-04 13:34 ` [PATCH] x86/alternatives: Fix ALTERNATIVE_2 padding generation properly Borislav Petkov
2015-04-07 9:27 ` Quentin Casasnovas
2015-04-07 9:40 ` [tip:x86/asm] " tip-bot for Borislav Petkov
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