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

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Date:	Tue, 14 Jun 2016 21:19:16 +0200
From:	Borislav Petkov <bp@...en8.de>
To:	Dave Hansen <dave.hansen@...ux.intel.com>
Cc:	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, hpa@...or.com,
	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 Tue, Jun 14, 2016 at 11:54:24AM -0700, Dave Hansen wrote:
> Lukasz, Borislav suggested using static_cpu_has_bug(), which will do the
> alternatives patching.  It's definitely the right thing to use here.

Yeah, either that or do an

alternative_call(null_func, fix_pte_peak, X86_BUG_PTE_LEAK, ...)

or so and you'll need a dummy function to call on !X86_BUG_PTE_LEAK
CPUs.

The static_cpu_has_bug() thing should be most likely a penalty
of a single JMP (I have to look at the asm) but then since the
callers are inlined, you'll have to patch all those places where
*ptep_get_and_clear() get inlined.

Shouldn't be a big deal still but...

"debug-alternative" and a kvm guest should help you there to get a quick
idea.

HTH.

-- 
Regards/Gruss,
    Boris.

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