From: Tom Lendacky <thomas.lendacky@amd.com>
To: "Van De Ven, Arjan" <arjan.van.de.ven@intel.com>,
"Woodhouse, David" <dwmw@amazon.co.uk>,
"linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>,
"x86@kernel.org" <x86@kernel.org>,
"Mallick, Asit K" <asit.k.mallick@intel.com>
Cc: "tim.c.chen@linux.intel.com" <tim.c.chen@linux.intel.com>,
"peterz@infradead.org" <peterz@infradead.org>,
"torvalds@linux-foundation.org" <torvalds@linux-foundation.org>,
"tglx@linutronix.de" <tglx@linutronix.de>,
"jpoimboe@redhat.com" <jpoimboe@redhat.com>,
"ak@linux.intel.com" <ak@linux.intel.com>,
"Williams, Dan J" <dan.j.williams@intel.com>,
"riel@redhat.com" <riel@redhat.com>,
"keescook@google.com" <keescook@google.com>,
"luto@kernel.org" <luto@kernel.org>,
"pjt@google.com" <pjt@google.com>, "bp@alien8.de" <bp@alien8.de>,
"Hansen, Dave" <dave.hansen@intel.com>,
"jikos@kernel.org" <jikos@kernel.org>,
"gregkh@linux-foundation.org" <gregkh@linux-foundation.org>
Subject: Re: [PATCH v1] x86/retpoline: Use lfence in the retpoline/RSB filling RSB macros
Date: Sat, 13 Jan 2018 15:13:45 -0600 [thread overview]
Message-ID: <ef080a43-5a07-b4d0-c43e-60bf9da71728@amd.com> (raw)
In-Reply-To: <0575AF4FD06DD142AD198903C74E1CC87A5C7FE4@FMSMSX151.amr.corp.intel.com>
On 1/13/2018 8:07 AM, Van De Ven, Arjan wrote:
>>> The RSB filling macro is applicable to AMD, and, if software is unable to
>>> verify that lfence is serializing on AMD (possible when running under a
>>> hypervisor), the generic retpoline support will be used and, so, is also
>>> applicable to AMD. Change the use of pause to lfence.
>>>
>>> Signed-off-by: Tom Lendacky <thomas.lendacky@amd.com>
>>
>> Conditionally-Acked-by: David Woodhouse <dwmw@amazon.co.uk>
>
>
> pause is technically the "save me power" instruction
>
> how about a compromise where we do a double:
>
> pause
> lfence
> jmp <up>
>
> as sequence... that way if the branch recovery is fast, we get the performance of pause, but if it takes a while, on AMD you get the behavior of lfence?
That should work on AMD.
Thanks,
Tom
>
>
next prev parent reply other threads:[~2018-01-13 21:13 UTC|newest]
Thread overview: 8+ messages / expand[flat|nested] mbox.gz Atom feed top
2018-01-13 1:07 Tom Lendacky
2018-01-13 1:53 ` Dan Williams
2018-01-13 2:22 ` Tom Lendacky
2018-01-13 10:33 ` [tip:x86/pti] x86/retpoline: Use LFENCE instead of PAUSE " tip-bot for Tom Lendacky
2018-01-13 10:46 ` [PATCH v1] x86/retpoline: Use lfence " Woodhouse, David
2018-01-13 14:07 ` Van De Ven, Arjan
2018-01-13 21:13 ` Tom Lendacky [this message]
2018-01-13 21:36 ` Thomas Gleixner
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=ef080a43-5a07-b4d0-c43e-60bf9da71728@amd.com \
--to=thomas.lendacky@amd.com \
--cc=ak@linux.intel.com \
--cc=arjan.van.de.ven@intel.com \
--cc=asit.k.mallick@intel.com \
--cc=bp@alien8.de \
--cc=dan.j.williams@intel.com \
--cc=dave.hansen@intel.com \
--cc=dwmw@amazon.co.uk \
--cc=gregkh@linux-foundation.org \
--cc=jikos@kernel.org \
--cc=jpoimboe@redhat.com \
--cc=keescook@google.com \
--cc=linux-kernel@vger.kernel.org \
--cc=luto@kernel.org \
--cc=peterz@infradead.org \
--cc=pjt@google.com \
--cc=riel@redhat.com \
--cc=tglx@linutronix.de \
--cc=tim.c.chen@linux.intel.com \
--cc=torvalds@linux-foundation.org \
--cc=x86@kernel.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
Powered by JetHome