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Re: [Xen-devel] Vanilla Linux and has_foreign_mapping

To: Michael Abd-El-Malek <mabdelmalek@xxxxxxx>
Subject: Re: [Xen-devel] Vanilla Linux and has_foreign_mapping
From: Jeremy Fitzhardinge <jeremy@xxxxxxxx>
Date: Tue, 29 Apr 2008 10:32:22 -0700
Cc: Mark McLoughlin <markmc@xxxxxxxxxx>, xen-devel <xen-devel@xxxxxxxxxxxxxxxxxxx>, Andrea Arcangeli <andrea@xxxxxxxxxxxx>, Eduardo Habkost <ehabkost@xxxxxxxxxx>, Keir Fraser <keir.fraser@xxxxxxxxxxxxx>, Christoph Lameter <clameter@xxxxxxx>
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Michael Abd-El-Malek wrote:
Some drivers may need to do additional tasks besides just clearing the PTE. For example, when unzapping my kernel PTE, I need to restore the physical mapping of the page. (On the initial set_pte (which I've overridden), I removed the physical backing of the page.)

If we really want to avoid a zap_pte hook, I suppose we can add flags to the page/PTE that indicate things like "this page needs to have its physical backing restored".

Is that something that needs to happen synchronously with the unmap, or could the driver do it in its vma callback? What do you mean by remove/restoring the physical backing? Do any of the in-tree drivers do this?

In the PAE case, which I think we can regard as usual these days, we have 64-bits to store per-mapping info, so stashing a callback or callback index seems pretty straightforward if we need full generality.


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