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From: Andi Kleen <ak@linux.intel.com>
To: speck@linutronix.de
Subject: [MODERATED] Re: [PATCH 2/4] RFC-MDSv1 0
Date: Mon, 12 Nov 2018 17:35:45 -0800	[thread overview]
Message-ID: <20181113013545.GI6218@tassilo.jf.intel.com> (raw)
In-Reply-To: <f6952dce-192e-e7ba-0f41-0df1b55f8ef7@citrix.com>

On Tue, Nov 13, 2018 at 12:07:47AM +0000, speck for Andrew Cooper wrote:
> On 12/11/2018 03:41, speck for Andi Kleen wrote:
> > @@ -329,6 +331,12 @@ For 32-bit we have the following conventions - kernel is built with
> >  
> >  #endif
> >  
> > +.macro EXIT_MDS
> > +	/* Clear CPU buffers that could leak. Instruction must be in memory form. */
> > +	ALTERNATIVE "", __stringify(pushq $__USER_DS ; verw (%rsp) ; addq $8, %rsp),\
> > +		 X86_FEATURE_MB_CLEAR
> 
> The code sample from the slides is push $0.  Here, you are forcing an
> implicit access into the GDT by using a non-NUL selector, which is a
> compound performance hit.

Actually it should be the same as 0. I think the slides just use $0 because
they don't know which OS the sequence would be used on.

-Andi

  reply	other threads:[~2018-11-13  1:35 UTC|newest]

Thread overview: 15+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2018-11-12  3:41 [MODERATED] [PATCH 0/4] RFC-MDSv1 1 Andi Kleen
2018-11-12  3:41 ` [MODERATED] [PATCH 1/4] RFC-MDSv1 4 Andi Kleen
2018-11-12  3:41 ` [MODERATED] [PATCH 2/4] RFC-MDSv1 0 Andi Kleen
2018-11-13  0:07   ` [MODERATED] " Andrew Cooper
2018-11-13  1:35     ` Andi Kleen [this message]
2018-11-13 21:59       ` Andrew Cooper
2018-11-14  4:04         ` Andi Kleen
2018-12-09 18:12           ` Andrew Cooper
2018-11-13 20:47   ` Jiri Kosina
2018-11-13 21:04     ` Luck, Tony
2018-11-14  2:32     ` Andi Kleen
2018-11-12  3:41 ` [MODERATED] [PATCH 3/4] RFC-MDSv1 3 Andi Kleen
2018-11-12  3:41 ` [MODERATED] [PATCH 4/4] RFC-MDSv1 2 Andi Kleen
2018-11-12 22:36   ` [MODERATED] " Greg KH
2018-11-13  1:37     ` Andi Kleen

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