From: "Van De Ven, Arjan" <arjan.van.de.ven@intel.com>
To: "Woodhouse, David" <dwmw@amazon.co.uk>,
"thomas.lendacky@amd.com" <thomas.lendacky@amd.com>,
"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 14:07:35 +0000 [thread overview]
Message-ID: <0575AF4FD06DD142AD198903C74E1CC87A5C7FE4@FMSMSX151.amr.corp.intel.com> (raw)
In-Reply-To: <1515840369.22302.523.camel@amazon.co.uk>
> > 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?
next prev parent reply other threads:[~2018-01-13 14:07 UTC|newest]
Thread overview: 8+ messages / expand[flat|nested] mbox.gz Atom feed top
2018-01-13 1:07 [PATCH v1] x86/retpoline: Use lfence in the retpoline/RSB filling RSB macros 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 [this message]
2018-01-13 21:13 ` Tom Lendacky
2018-01-13 21:36 ` Thomas Gleixner
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