From: tip-bot for Andi Kleen <tipbot@zytor.com>
To: linux-tip-commits@vger.kernel.org
Cc: hpa@zytor.com, mingo@kernel.org, ak@linux.intel.com,
tglx@linutronix.de, dwmw@amazon.co.uk,
linux-kernel@vger.kernel.org
Subject: [tip:x86/pti] x86/retpoline: Optimize inline assembler for vmexit_fill_RSB
Date: Fri, 19 Jan 2018 07:49:06 -0800 [thread overview]
Message-ID: <tip-3f7d875566d8e79c5e0b2c9a413e91b2c29e0854@git.kernel.org> (raw)
In-Reply-To: <20180117225328.15414-1-andi@firstfloor.org>
Commit-ID: 3f7d875566d8e79c5e0b2c9a413e91b2c29e0854
Gitweb: https://git.kernel.org/tip/3f7d875566d8e79c5e0b2c9a413e91b2c29e0854
Author: Andi Kleen <ak@linux.intel.com>
AuthorDate: Wed, 17 Jan 2018 14:53:28 -0800
Committer: Thomas Gleixner <tglx@linutronix.de>
CommitDate: Fri, 19 Jan 2018 16:31:30 +0100
x86/retpoline: Optimize inline assembler for vmexit_fill_RSB
The generated assembler for the C fill RSB inline asm operations has
several issues:
- The C code sets up the loop register, which is then immediately
overwritten in __FILL_RETURN_BUFFER with the same value again.
- The C code also passes in the iteration count in another register, which
is not used at all.
Remove these two unnecessary operations. Just rely on the single constant
passed to the macro for the iterations.
Signed-off-by: Andi Kleen <ak@linux.intel.com>
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Acked-by: David Woodhouse <dwmw@amazon.co.uk>
Cc: dave.hansen@intel.com
Cc: gregkh@linuxfoundation.org
Cc: torvalds@linux-foundation.org
Cc: arjan@linux.intel.com
Link: https://lkml.kernel.org/r/20180117225328.15414-1-andi@firstfloor.org
---
arch/x86/include/asm/nospec-branch.h | 7 ++++---
1 file changed, 4 insertions(+), 3 deletions(-)
diff --git a/arch/x86/include/asm/nospec-branch.h b/arch/x86/include/asm/nospec-branch.h
index 19ba5ad..4ad4108 100644
--- a/arch/x86/include/asm/nospec-branch.h
+++ b/arch/x86/include/asm/nospec-branch.h
@@ -206,16 +206,17 @@ extern char __indirect_thunk_end[];
static inline void vmexit_fill_RSB(void)
{
#ifdef CONFIG_RETPOLINE
- unsigned long loops = RSB_CLEAR_LOOPS / 2;
+ unsigned long loops;
asm volatile (ANNOTATE_NOSPEC_ALTERNATIVE
ALTERNATIVE("jmp 910f",
__stringify(__FILL_RETURN_BUFFER(%0, RSB_CLEAR_LOOPS, %1)),
X86_FEATURE_RETPOLINE)
"910:"
- : "=&r" (loops), ASM_CALL_CONSTRAINT
- : "r" (loops) : "memory" );
+ : "=r" (loops), ASM_CALL_CONSTRAINT
+ : : "memory" );
#endif
}
+
#endif /* __ASSEMBLY__ */
#endif /* __NOSPEC_BRANCH_H__ */
prev parent reply other threads:[~2018-01-19 15:51 UTC|newest]
Thread overview: 3+ messages / expand[flat|nested] mbox.gz Atom feed top
2018-01-17 22:53 [PATCH] x86/retpoline: Optimize inline assembler for vmexit_fill_RSB Andi Kleen
2018-01-18 12:41 ` David Woodhouse
2018-01-19 15:49 ` tip-bot for Andi Kleen [this message]
Reply instructions:
You may reply publicly to this message via plain-text email
using any one of the following methods:
* Save the following mbox file, import it into your mail client,
and reply-to-all from there: mbox
Avoid top-posting and favor interleaved quoting:
https://en.wikipedia.org/wiki/Posting_style#Interleaved_style
* Reply using the --to, --cc, and --in-reply-to
switches of git-send-email(1):
git send-email \
--in-reply-to=tip-3f7d875566d8e79c5e0b2c9a413e91b2c29e0854@git.kernel.org \
--to=tipbot@zytor.com \
--cc=ak@linux.intel.com \
--cc=dwmw@amazon.co.uk \
--cc=hpa@zytor.com \
--cc=linux-kernel@vger.kernel.org \
--cc=linux-tip-commits@vger.kernel.org \
--cc=mingo@kernel.org \
--cc=tglx@linutronix.de \
/path/to/YOUR_REPLY
https://kernel.org/pub/software/scm/git/docs/git-send-email.html
* If your mail client supports setting the In-Reply-To header
via mailto: links, try the mailto: link
Be sure your reply has a Subject: header at the top and a blank line
before the message body.
This is a public inbox, see mirroring instructions
for how to clone and mirror all data and code used for this inbox;
as well as URLs for NNTP newsgroup(s).