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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: Wed, 05 Dec 2007 17:17:23 +0000
Cc: "xen-devel@xxxxxxxxxxxxxxxxxxx" <xen-devel@xxxxxxxxxxxxxxxxxxx>, Eduardo Habkost <ehabkost@xxxxxxxxxx>, Juan Quintela <quintela@xxxxxxxxxx>, "Stephen C. Tweedie" <sct@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:

Actually I'm not so sure now. Presumably you add VM_PFNMAP to make
vm_normal_page() return NULL? But actually I would expect pte_pfn() to
return max_mapnr because the mapped page is not a local page. And that
should cause vm_normal_page() to return NULL always, regardless of whether
you assert VM_PFNMAP. Is gntdev being used to grant-and-map local pages in
the test that causes the crash?

That's right (gntdev is being used to map (but not grant) a local page). The test case creates a virtual block device in Dom0, and attempts to map its ring buffer in a user-space daemon in Dom0. Therefore pte_pfn succeeds.

Regards,

Derek.

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