From: Thomas Gleixner <tglx@linutronix.de>
To: Tom Lendacky <thomas.lendacky@amd.com>
Cc: "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>,
"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>,
"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 22:36:13 +0100 (CET) [thread overview]
Message-ID: <alpine.DEB.2.20.1801132235390.2371@nanos> (raw)
In-Reply-To: <ef080a43-5a07-b4d0-c43e-60bf9da71728@amd.com>
[-- Attachment #1: Type: text/plain, Size: 967 bytes --]
On Sat, 13 Jan 2018, Tom Lendacky wrote:
> 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.
I zapped the commit from tip for now until this discussion is resolved.
Thanks,
tglx
prev parent reply other threads:[~2018-01-13 21:36 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
2018-01-13 21:13 ` Tom Lendacky
2018-01-13 21:36 ` Thomas Gleixner [this message]
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