linux-kernel - Re: [PATCH] fix pgd

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Message-Id: <4D63D4CD020000780003320A@vpn.id2.novell.com>
Date:	Tue, 22 Feb 2011 14:22:53 +0000
From:	"Jan Beulich" <JBeulich@...ell.com>
To:	"Andrea Arcangeli" <aarcange@...hat.com>
Cc:	"Ian Campbell" <Ian.Campbell@...rix.com>,
	"Andi Kleen" <andi@...stfloor.org>,
	"Hugh Dickins" <hughd@...gle.com>,
	"Jeremy Fitzhardinge" <jeremy@...p.org>,
	"the arch/x86 maintainers" <x86@...nel.org>,
	"Thomas Gleixner" <tglx@...utronix.de>,
	"Andrew Morton" <akpm@...ux-foundation.org>,
	"Xen-devel@...ts.xensource.com" <Xen-devel@...ts.xensource.com>,
	"Konrad Rzeszutek Wilk" <konrad.wilk@...cle.com>,
	"Johannes Weiner" <jweiner@...hat.com>,
	"Larry Woodman" <lwoodman@...hat.com>,
	"Rik van Riel" <riel@...hat.com>,
	"Linux Kernel Mailing List" <linux-kernel@...r.kernel.org>,
	"H. Peter Anvin" <hpa@...or.com>
Subject: Re: [PATCH] fix pgd_lock deadlock

>>> On 22.02.11 at 14:49, Andrea Arcangeli <aarcange@...hat.com> wrote:
> On Tue, Feb 22, 2011 at 07:48:54AM +0000, Jan Beulich wrote:
>> A possible alternative would be to acquire the page table lock
>> in vmalloc_sync_all() only in the Xen case (perhaps by storing
>> NULL into page->index in pgd_set_mm() when not running on
>> Xen). This is utilizing the fact that there aren't (supposed to
>> be - for non-pvops this is definitely the case) any TLB flush IPIs
>> under Xen, and hence the race you're trying to fix doesn't
>> exist there (while non-Xen doesn't need the extra locking).
> 
> That's sure ok with me. Can we use a global runtime to check if the
> guest is running under Xen paravirt, instead of passing that info
> through page->something?

If everyone's okay with putting a couple of "if (xen_pv_domain())"
into mm/fault.c - sure. I would have thought that this wouldn't be
liked, hence the suggestion to make this depend on seeing the
backlink be non-NULL.

Jan

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