linux-kernel - Re: [PATCH] fix pgd

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Message-ID: <20110222134956.GU13092@random.random>
Date:	Tue, 22 Feb 2011 14:49:56 +0100
From:	Andrea Arcangeli <aarcange@...hat.com>
To:	Jan Beulich <JBeulich@...ell.com>
Cc:	Johannes Weiner <jweiner@...hat.com>,
	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>,
	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 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?
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