linux-kernel - Re: [PATCH v2] Linux VM workaround for Knights Landing A/D leak

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Message-ID: <B9213B85-0761-42BB-B546-60E92ABAC13A@zytor.com>
Date:	Tue, 14 Jun 2016 14:13:48 -0700
From:	"H. Peter Anvin" <hpa@...or.com>
To:	Borislav Petkov <bp@...en8.de>
CC:	Dave Hansen <dave.hansen@...ux.intel.com>,
	One Thousand Gnomes <gnomes@...rguk.ukuu.org.uk>,
	Lukasz Anaczkowski <lukasz.anaczkowski@...el.com>,
	linux-kernel@...r.kernel.org, linux-mm@...ck.org,
	tglx@...utronix.de, mingo@...hat.com, ak@...ux.intel.com,
	kirill.shutemov@...ux.intel.com, mhocko@...e.com,
	akpm@...ux-foundation.org, harish.srinivasappa@...el.com,
	lukasz.odzioba@...el.com, grzegorz.andrejczuk@...el.com,
	lukasz.daniluk@...el.com
Subject: Re: [PATCH v2] Linux VM workaround for Knights Landing A/D leak

On June 14, 2016 2:02:55 PM PDT, Borislav Petkov <bp@...en8.de> wrote:
>On Tue, Jun 14, 2016 at 01:54:25PM -0700, H. Peter Anvin wrote:
>> There was that.  It is still possible that we end up with NOP a JMP
>> right before another JMP; we could perhaps make the patching code
>> smarter and see if we have a JMP immediately after.
>
>Yeah, I still can't get reproduce that reliably - I remember seeing it
>at some point but then dismissing it for another, higher-prio thing.
>And
>now the whole memory is hazy at best.
>
>But, you're giving me a great idea right now - I have this kernel
>disassembler tool which dumps alternative sections already and I could
>teach it to look for pathological cases around the patching sites and
>scream.
>
>Something for my TODO list when I get a quiet moment.
>
>Thanks!

We talked with the GCC people about always bias asm goto toward the first label even if followed by __builtin_unreachable().  I don't know if that happened; if so we should probably insert the unreachable for those versions of gcc only.
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