From mboxrd@z Thu Jan  1 00:00:00 1970
From: "H. Peter Anvin" <hpa@zytor.com>
Subject: Re: [PATCH v2] Linux VM workaround for Knights Landing A/D leak
Date: Tue, 14 Jun 2016 13:54:25 -0700
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To: Borislav Petkov <bp@alien8.de>
Cc: Dave Hansen <dave.hansen@linux.intel.com>, One Thousand Gnomes <gnomes@lxorguk.ukuu.org.uk>, Lukasz Anaczkowski <lukasz.anaczkowski@intel.com>, linux-kernel@vger.kernel.org, linux-mm@kvack.org, tglx@linutronix.de, mingo@redhat.com, ak@linux.intel.com, kirill.shutemov@linux.intel.com, mhocko@suse.com, akpm@linux-foundation.org, harish.srinivasappa@intel.com, lukasz.odzioba@intel.com, grzegorz.andrejczuk@intel.com, lukasz.daniluk@intel.com
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On 06/14/16 13:47, Borislav Petkov wrote:
> On Tue, Jun 14, 2016 at 01:20:06PM -0700, H. Peter Anvin wrote:
>> static_cpu_has_bug() should turn into 5-byte NOP in the common (bugless)
>> case.
> 
> Yeah, it does. I looked at the asm.
> 
> I wasn't 100% sure because I vaguely remember gcc reordering things in
> some pathological case but I'm most likely remembering wrong because if
> it were doing that, then the whole nopping out won't work. F'get about
> it. :)
> 

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.

	-hpa