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Re: [Xen-devel] RFC: [0/2] Remove netloop by lazy copying in netback

To: Herbert Xu <herbert@xxxxxxxxxxxxxxxxxxx>
Subject: Re: [Xen-devel] RFC: [0/2] Remove netloop by lazy copying in netback
From: Keir Fraser <Keir.Fraser@xxxxxxxxxxxx>
Date: Tue, 27 Mar 2007 01:33:58 +0100
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On 26/3/07 22:08, "Herbert Xu" <herbert@xxxxxxxxxxxxxxxxxxx> wrote:

>> Can't we wrap the 'swap around' critical section in an irq-safe spinlock?
>> All we'd need to do from the page-fault handler then is a barrier on that
>> spinlock (i.e, wait for it to be released). Netback can simply copy the page
>> to new memory frame, unmap the grant, then relocate the new memory frame's
>> pseudophysical address.
> That works fine for the x86 case.  But when it's auto-translated,
> you won't even get a page fault in the guest because the guest PTE
> is unchanged and completely valid.

How about you invalidate the PTE for the duration of the critical section.
It's a bit skanky, but would work around this issue quite nicely!

 -- Keir

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