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[Xen-devel] Re: [PATCH] fix pgd_lock deadlock

To: "Andrea Arcangeli" <aarcange@xxxxxxxxxx>
Subject: [Xen-devel] Re: [PATCH] fix pgd_lock deadlock
From: "Jan Beulich" <JBeulich@xxxxxxxxxx>
Date: Tue, 22 Feb 2011 14:22:53 +0000
Cc: Jeremy Fitzhardinge <jeremy@xxxxxxxx>, "Xen-devel@xxxxxxxxxxxxxxxxxxx" <Xen-devel@xxxxxxxxxxxxxxxxxxx>, Ian Campbell <Ian.Campbell@xxxxxxxxxx>, Konrad Rzeszutek Wilk <konrad.wilk@xxxxxxxxxx>, Larry Woodman <lwoodman@xxxxxxxxxx>, Linux Kernel Mailing List <linux-kernel@xxxxxxxxxxxxxxx>, the arch/x86 maintainers <x86@xxxxxxxxxx>, Hugh Dickins <hughd@xxxxxxxxxx>, Johannes Weiner <jweiner@xxxxxxxxxx>, Andi Kleen <andi@xxxxxxxxxxxxxx>, "H. Peter Anvin" <hpa@xxxxxxxxx>, Thomas Gleixner <tglx@xxxxxxxxxxxxx>, Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>
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>>> On 22.02.11 at 14:49, Andrea Arcangeli <aarcange@xxxxxxxxxx> 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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