llvm dev - Jan 2018 - FYI, we've posted a component of Spectre mitigation on llvm-commits

Sending a note here as this seems likely to be of relatively broad interest.

Thread:
http://lists.llvm.org/pipermail/llvm-commits/Week-of-Mon-20180101/513630.html

Review link:
https://reviews.llvm.org/D41723#
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On 4 January 2018 at 10:23, Chandler Carruth via llvm-dev
<llvm-dev at lists.llvm.org> wrote:
> Sending a note here as this seems likely to be of relatively broad
interest.
>
> Thread:
>
http://lists.llvm.org/pipermail/llvm-commits/Week-of-Mon-20180101/513630.html
>
> Review link:
> https://reviews.llvm.org/D41723#
It seems the review link is getting wider coverage (Reddit, HN, ...)
and Phabricator is struggling under the load.

Best,

Alex

The folks working on phab are busily propping it up. It should be
relatively healthy now.

On Thu, Jan 4, 2018 at 9:20 AM Alex Bradbury via llvm-dev <
llvm-dev at lists.llvm.org> wrote:
> On 4 January 2018 at 10:23, Chandler Carruth via llvm-dev
> <llvm-dev at lists.llvm.org> wrote:
> > Sending a note here as this seems likely to be of relatively broad
> interest.
> >
> > Thread:
> >
>
http://lists.llvm.org/pipermail/llvm-commits/Week-of-Mon-20180101/513630.html
> >
> > Review link:
> > https://reviews.llvm.org/D41723#
>
> It seems the review link is getting wider coverage (Reddit, HN, ...)
> and Phabricator is struggling under the load.
>
> Best,
>
> Alex
> _______________________________________________
> LLVM Developers mailing list
> llvm-dev at lists.llvm.org
> http://lists.llvm.org/cgi-bin/mailman/listinfo/llvm-dev
>
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> On Jan 4, 2018, at 04:23, Chandler Carruth via llvm-dev <llvm-dev at
lists.llvm.org> wrote:
> 
> Sending a note here as this seems likely to be of relatively broad
interest.
It looks like this is producing code of the following form.

	call	next
loop:
	pause
	jmp	loop
next:
	mov	[rsp], r11
	ret

As I understand it, the busy loop is to cause the speculative execution to be
trapped in the loop. Was something like ud2 considered? I presume that would
stop the speculative execution without involving any of the execution units the
way the busy loop does.

-- 
Stephen Checkoway

On Thu, Jan 4, 2018 at 12:31 PM Stephen Checkoway via llvm-dev <
llvm-dev at lists.llvm.org> wrote:
>
> > On Jan 4, 2018, at 04:23, Chandler Carruth via llvm-dev <
> llvm-dev at lists.llvm.org> wrote:
> >
> > Sending a note here as this seems likely to be of relatively broad
> interest.
>
> It looks like this is producing code of the following form.
>
>         call    next
> loop:
>         pause
>         jmp     loop
> next:
>         mov     [rsp], r11
>         ret
>
> As I understand it, the busy loop is to cause the speculative execution to
> be trapped in the loop. Was something like ud2 considered? I presume that
> would stop the speculative execution without involving any of the execution
> units the way the busy loop does.
>
The pause instruction will also avoid tying up execution resources in
speculative contexts, so I wouldn't expect it to be significantly different.

>
> --
> Stephen Checkoway
>
>
>
> _______________________________________________
> LLVM Developers mailing list
> llvm-dev at lists.llvm.org
> http://lists.llvm.org/cgi-bin/mailman/listinfo/llvm-dev
>
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Thanks for the notification, Chandler.

I also wanted to note that I’ve just posted another component for Spectre
mitigation (variant 1), see https://reviews.llvm.org/D41760 and
https://reviews.llvm.org/D41761.
I believe this is completely complementary to the retpoline mitigation you
pointed to at https://reviews.llvm.org/D41723#, which is targeted at mitigating
variant 2.

Thanks,

Kristof

On 4 Jan 2018, at 11:23, Chandler Carruth via llvm-dev <llvm-dev at
lists.llvm.org<mailto:llvm-dev at lists.llvm.org>> wrote:

Sending a note here as this seems likely to be of relatively broad interest.

Thread:
http://lists.llvm.org/pipermail/llvm-commits/Week-of-Mon-20180101/513630.html

Review link:
https://reviews.llvm.org/D41723#
_______________________________________________
LLVM Developers mailing list
llvm-dev at lists.llvm.org<mailto:llvm-dev at lists.llvm.org>
http://lists.llvm.org/cgi-bin/mailman/listinfo/llvm-dev

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Awesome, replied.

We've been working on similar things, but didn't have them
ready-to-publish
due to slightly lower urgency (there are reasonable ways to locally mimic
these kinds of things in sensitive areas like the Linux kernel, and even
finding code patterns for variant #1 is substantially harder). We have some
significantly different APIs we'd like to discuss here based on experience
trying to implement these on x86 and deploy them to a reasonably large body
of code. Hopefully more details soon as folks have time.

On Fri, Jan 5, 2018 at 6:15 AM Kristof Beyls <Kristof.Beyls at arm.com>
wrote:
> Thanks for the notification, Chandler.
>
> I also wanted to note that I’ve just posted another component for Spectre
> mitigation (variant 1), see https://reviews.llvm.org/D41760 and
> https://reviews.llvm.org/D41761.
> I believe this is completely complementary to the retpoline mitigation you
> pointed to at https://reviews.llvm.org/D41723#, which is targeted at
> mitigating variant 2.
>
> Thanks,
>
> Kristof
>
> On 4 Jan 2018, at 11:23, Chandler Carruth via llvm-dev <
> llvm-dev at lists.llvm.org> wrote:
>
> Sending a note here as this seems likely to be of relatively broad
> interest.
>
> Thread:
>
>
http://lists.llvm.org/pipermail/llvm-commits/Week-of-Mon-20180101/513630.html
>
> Review link:
> https://reviews.llvm.org/D41723#
>
> _______________________________________________
> LLVM Developers mailing list
> llvm-dev at lists.llvm.org
> http://lists.llvm.org/cgi-bin/mailman/listinfo/llvm-dev
>
>
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