From: Denys Vlasenko <dvlasenk@redhat.com>
To: David Laight <David.Laight@ACULAB.COM>,
"hpa@zytor.com" <hpa@zytor.com>,
"torvalds@linux-foundation.org" <torvalds@linux-foundation.org>,
"luto@kernel.org" <luto@kernel.org>,
"mingo@kernel.org" <mingo@kernel.org>,
"bp@alien8.de" <bp@alien8.de>,
"linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>,
"linux@dominikbrodowski.net" <linux@dominikbrodowski.net>,
"brgerst@gmail.com" <brgerst@gmail.com>,
"peterz@infradead.org" <peterz@infradead.org>,
"tglx@linutronix.de" <tglx@linutronix.de>,
"jpoimboe@redhat.com" <jpoimboe@redhat.com>,
"linux-tip-commits@vger.kernel.org"
<linux-tip-commits@vger.kernel.org>
Subject: Re: [tip:x86/pti] x86/entry/64: Introduce the PUSH_AND_CLEAN_REGS macro
Date: Mon, 12 Feb 2018 14:43:50 +0100 [thread overview]
Message-ID: <6217451a-21ea-5fc3-54f7-1e333452dcda@redhat.com> (raw)
In-Reply-To: <1b5552f1231b4c9b867a17d0c5c594bb@AcuMS.aculab.com>
On 02/12/2018 02:36 PM, David Laight wrote:
> From: Denys Vlasenko
>> Sent: 12 February 2018 13:29
> ...
>>>
>>> x86/entry/64: Introduce the PUSH_AND_CLEAN_REGS macro
>>>
>>> Those instances where ALLOC_PT_GPREGS_ON_STACK is called just before
>>> SAVE_AND_CLEAR_REGS can trivially be replaced by PUSH_AND_CLEAN_REGS.
>>> This macro uses PUSH instead of MOV and should therefore be faster, at
>>> least on newer CPUs.
> ...
>>> Link: http://lkml.kernel.org/r/20180211104949.12992-5-linux@dominikbrodowski.net
>>> Signed-off-by: Ingo Molnar <mingo@kernel.org>
>>> ---
>>> arch/x86/entry/calling.h | 36 ++++++++++++++++++++++++++++++++++++
>>> arch/x86/entry/entry_64.S | 6 ++----
>>> 2 files changed, 38 insertions(+), 4 deletions(-)
>>>
>>> diff --git a/arch/x86/entry/calling.h b/arch/x86/entry/calling.h
>>> index a05cbb8..57b1b87 100644
>>> --- a/arch/x86/entry/calling.h
>>> +++ b/arch/x86/entry/calling.h
>>> @@ -137,6 +137,42 @@ For 32-bit we have the following conventions - kernel is built with
>>> UNWIND_HINT_REGS offset=\offset
>>> .endm
>>>
>>> + .macro PUSH_AND_CLEAR_REGS
>>> + /*
>>> + * Push registers and sanitize registers of values that a
>>> + * speculation attack might otherwise want to exploit. The
>>> + * lower registers are likely clobbered well before they
>>> + * could be put to use in a speculative execution gadget.
>>> + * Interleave XOR with PUSH for better uop scheduling:
>>> + */
>>> + pushq %rdi /* pt_regs->di */
>>> + pushq %rsi /* pt_regs->si */
>>> + pushq %rdx /* pt_regs->dx */
>>> + pushq %rcx /* pt_regs->cx */
>>> + pushq %rax /* pt_regs->ax */
>>> + pushq %r8 /* pt_regs->r8 */
>>> + xorq %r8, %r8 /* nospec r8 */
>>
>> xorq's are slower than xorl's on Silvermont/Knights Landing.
>> I propose using xorl instead.
>
> Does using movq to copy the first zero to the other registers make
> the code any faster?
>
> ISTR mov reg-reg is often implemented as a register rename rather than an
> alu operation.
xorl is implemented in register rename as well. Just, for some reason,
xorq did not get the same treatment on those CPUs.
next prev parent reply other threads:[~2018-02-12 13:43 UTC|newest]
Thread overview: 33+ messages / expand[flat|nested] mbox.gz Atom feed top
2018-02-11 10:49 [PATCH v3 0/7] x86/entry: simplify and unify SAVE/POP_REGS Dominik Brodowski
2018-02-11 10:49 ` [PATCH v3 1/7] x86/entry: merge SAVE_C_REGS and SAVE_EXTRA_REGS, remove unused extensions Dominik Brodowski
2018-02-12 10:15 ` [tip:x86/pti] x86/entry/64: Merge " tip-bot for Dominik Brodowski
2018-02-13 9:00 ` tip-bot for Dominik Brodowski
2018-02-11 10:49 ` [PATCH v3 2/7] x86/entry: merge POP_C_REGS and POP_EXTRA_REGS Dominik Brodowski
2018-02-12 10:16 ` [tip:x86/pti] x86/entry/64: Merge the POP_C_REGS and POP_EXTRA_REGS macros into a single POP_REGS macro tip-bot for Dominik Brodowski
2018-02-13 9:01 ` tip-bot for Dominik Brodowski
2018-02-11 10:49 ` [PATCH v3 3/7] x86/entry: interleave XOR register clearing with PUSH instructions Dominik Brodowski
2018-02-12 10:16 ` [tip:x86/pti] x86/entry/64: Interleave " tip-bot for Dominik Brodowski
2018-02-13 9:01 ` tip-bot for Dominik Brodowski
2018-02-11 10:49 ` [PATCH v3 4/7] x86/entry: introduce PUSH_AND_CLEAN_REGS Dominik Brodowski
2018-02-12 10:17 ` [tip:x86/pti] x86/entry/64: Introduce the PUSH_AND_CLEAN_REGS macro tip-bot for Dominik Brodowski
2018-02-12 13:29 ` Denys Vlasenko
2018-02-12 13:36 ` David Laight
2018-02-12 13:43 ` Denys Vlasenko [this message]
2018-02-12 16:51 ` Linus Torvalds
2018-02-13 9:01 ` tip-bot for Dominik Brodowski
2018-02-11 10:49 ` [PATCH v3 5/7] x86/entry: use PUSH_AND_CLEAN_REGS in more cases Dominik Brodowski
2018-02-12 10:17 ` [tip:x86/pti] x86/entry/64: Use " tip-bot for Dominik Brodowski
2018-02-13 9:02 ` tip-bot for Dominik Brodowski
2018-02-11 10:49 ` [PATCH v3 6/7] x86/entry: get rid of ALLOC_PT_GPREGS_ON_STACK and SAVE_AND_CLEAR_REGS Dominik Brodowski
2018-02-12 10:18 ` [tip:x86/pti] x86/entry/64: Get rid of the ALLOC_PT_GPREGS_ON_STACK and SAVE_AND_CLEAR_REGS macros tip-bot for Dominik Brodowski
2018-02-13 9:02 ` tip-bot for Dominik Brodowski
2018-02-11 10:49 ` [PATCH v3 7/7] x86/entry: indent PUSH_AND_CLEAR_REGS and POP_REGS properly Dominik Brodowski
2018-02-12 10:18 ` [tip:x86/pti] x86/entry/64: Indent " tip-bot for Dominik Brodowski
2018-02-12 20:13 ` [PATCH] x86/entry/64: Remove unused icebp macro Borislav Petkov
2018-02-13 7:36 ` Ingo Molnar
2018-02-13 9:04 ` [tip:x86/pti] x86/entry/64: Remove the unused 'icebp' macro tip-bot for Borislav Petkov
2018-02-13 9:03 ` [tip:x86/pti] x86/entry/64: Indent PUSH_AND_CLEAR_REGS and POP_REGS properly tip-bot for Dominik Brodowski
2018-02-11 10:49 ` [PATCH v3 8/7] TESTING_ONLY x86/entry: reduce static footprint of idtentry Dominik Brodowski
2018-02-12 9:37 ` Ingo Molnar
2018-02-12 19:17 ` Linus Torvalds
2018-02-13 12:41 ` Ingo Molnar
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=6217451a-21ea-5fc3-54f7-1e333452dcda@redhat.com \
--to=dvlasenk@redhat.com \
--cc=David.Laight@ACULAB.COM \
--cc=bp@alien8.de \
--cc=brgerst@gmail.com \
--cc=hpa@zytor.com \
--cc=jpoimboe@redhat.com \
--cc=linux-kernel@vger.kernel.org \
--cc=linux-tip-commits@vger.kernel.org \
--cc=linux@dominikbrodowski.net \
--cc=luto@kernel.org \
--cc=mingo@kernel.org \
--cc=peterz@infradead.org \
--cc=tglx@linutronix.de \
--cc=torvalds@linux-foundation.org \
/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).