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Re: [Xen-devel] Re: Next steps with pv_ops for Xen

To: Keir Fraser <Keir.Fraser@xxxxxxxxxxxx>
Subject: Re: [Xen-devel] Re: Next steps with pv_ops for Xen
From: Derek Murray <Derek.Murray@xxxxxxxxxxxx>
Date: Thu, 06 Dec 2007 10:00:06 +0000
Cc: Jeremy Fitzhardinge <jeremy@xxxxxxxx>, "xen-devel@xxxxxxxxxxxxxxxxxxx" <xen-devel@xxxxxxxxxxxxxxxxxxx>, Eduardo Habkost <ehabkost@xxxxxxxxxx>, Juan Quintela <quintela@xxxxxxxxxx>, Jan Beulich <jbeulich@xxxxxxxxxx>, Glauber de Oliveira Costa <gcosta@xxxxxxxxxx>, Chris Wright <chrisw@xxxxxxxxxxxx>, "virtualization@xxxxxxxxxxxxxx" <virtualization@xxxxxxxxxxxxxx>, Gerd Hoffmann <kraxel@xxxxxxxxxx>
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Keir Fraser wrote:
You'd need to track pte->grant_handle mappings somewhere, but it could
certainly be done this way, yes.

At the moment, blktap and gntdev provide struct pages to get_user_pages by smuggling them in the vm_private_data field of the relevant vm_area_struct. Could we use this field to get the handles to ptep_get_and_clear_full as well?

Only downside that I can see is that we would need to find the vma for each PTE that needs to be cleared this way (since we don't get this passed to ptep_get_and_clear_full), but this is mitigated by (i) it only happening in the erroneous, unclean-shutdown case, and (ii) getting a hit in the mm->mmap_cache for consecutive runs of mapped grants.

Regards,

Derek.

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