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

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Message-Id: <613007E2-2A88-4934-9364-A5A66A555305@gmail.com>
Date:	Wed, 15 Jun 2016 13:04:48 -0700
From:	Nadav Amit <nadav.amit@...il.com>
To:	"Anaczkowski, Lukasz" <lukasz.anaczkowski@...el.com>
Cc:	LKML <linux-kernel@...r.kernel.org>,
	"linux-mm@...ck.org" <linux-mm@...ck.org>,
	Thomas Gleixner <tglx@...utronix.de>,
	Ingo Molnar <mingo@...hat.com>,
	Dave Hansen <dave.hansen@...ux.intel.com>,
	"ak@...ux.intel.com" <ak@...ux.intel.com>,
	"kirill.shutemov@...ux.intel.com" <kirill.shutemov@...ux.intel.com>,
	"mhocko@...e.com" <mhocko@...e.com>,
	Andrew Morton <akpm@...ux-foundation.org>,
	"H. Peter Anvin" <hpa@...or.com>,
	"Srinivasappa, Harish" <harish.srinivasappa@...el.com>,
	"Odzioba, Lukasz" <lukasz.odzioba@...el.com>,
	"Andrejczuk, Grzegorz" <grzegorz.andrejczuk@...el.com>,
	"Daniluk, Lukasz" <lukasz.daniluk@...el.com>
Subject: Re: [PATCH v2] Linux VM workaround for Knights Landing A/D leak

Lukasz <lukasz.anaczkowski@...el.com> wrote:

> From: Nadav Amit [mailto:nadav.amit@...il.com] 
> Sent: Tuesday, June 14, 2016 8:38 PM
> 
>>> +	pte_t pte = ptep_get_and_clear(mm, addr, ptep);
>>> +
>>> +	if (boot_cpu_has_bug(X86_BUG_PTE_LEAK))
>>> +		fix_pte_leak(mm, addr, ptep);
>>> +	return pte;
>>> }
>> 
>> I missed it on the previous iteration: ptep_get_and_clear already calls 
>> fix_pte_leak when needed. So do you need to call it again here?
> 
> You're right, Nadav. Not needing this. Will be removed in next version of the patch.

Be careful here. According to the SDM when invalidating a huge-page,
each 4KB page needs to be invalidated separately. In practice, when
Linux invalidates 2MB/1GB pages it performs a full TLB flush. The
full flush may not be required on knights landing, and specifically
for the workaround, but you should check.  

Regards,
Nadav