linux-kernel - Re: [PATCH] x86, hugetlb: add missing TLB page invalidation for hugetlb

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Date:	Sat, 17 May 2014 11:24:14 +0200
From:	Anthony Iliopoulos <anthony.iliopoulos@...wei.com>
To:	Oren Twaig <oren@...lemp.com>
CC:	Dave Hansen <dave@...1.net>, Thomas Gleixner <tglx@...utronix.de>,
	"Ingo Molnar" <mingo@...hat.com>, "H. Peter Anvin" <hpa@...or.com>,
	<x86@...nel.org>, <linux-kernel@...r.kernel.org>,
	"Kirill A. Shutemov" <kirill.shutemov@...ux.intel.com>,
	Shay Goikhman <shay.goikhman@...wei.com>,
	Paul Mundt <paul.mundt@...wei.com>,
	Carlos Villavieja <villavieja@....utexas.edu>,
	Nacho Navarro <nacho.navarro@....es>,
	"Avi Mendelson" <avi.mendelson@....technion.ac.il>,
	Yoav Etsion <yetsion@....technion.ac.il>,
	Gerald Schaefer <gerald.schaefer@...ibm.com>,
	David Gibson <david@...son.dropbear.id.au>,
	linux-arch <linux-arch@...r.kernel.org>
Subject: Re: [PATCH] x86, hugetlb: add missing TLB page invalidation for
 hugetlb_cow()

Hi Oren,

On Thu, May 15, 2014 at 10:05:05AM +0300, Oren Twaig wrote:
> 
> On 05/15/2014 08:00 PM, Anthony Iliopoulos wrote:
> > I have dismissed this case, since I assume that there are many more
> > cycles spent in servicing the TLB invalidation IPI, walking the pgtable
> > plus other related overhead (e.g. sched) than in updating the pte/pmd
> > so I am not sure how possible it would be to hit this condition.
> 
> Hi Anthony,
> 
> I have a question about the above statement. What will happen with multi
> cpu VMs ? won't the race described above can happen ? I.e one virtual CPU
> can will visit the host and the other will continue to encounter your race ?

I don't think there will be any race for the vcpu cases, since the sptes
will be cleared via the mmu_notifier, so this should take care of it
in the same manner as ptep_get_and_clear() does, as described by Dave
earlier in this thread.

Regards,
Anthony
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