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

["Jan Beulich" <JBeulich@xxxxxxxxxx>]

>>> 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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