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Re: [Xen-devel] [PATCH 2/4] x86: relax a few get_gfn() invocations
- To: Jan Beulich <JBeulich@xxxxxxxx>, xen-devel <xen-devel@xxxxxxxxxxxxxxxxxxxx>
- From: George Dunlap <george.dunlap@xxxxxxxxxx>
- Date: Fri, 5 Apr 2019 11:30:05 +0100
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- Cc: George Dunlap <George.Dunlap@xxxxxxxxxxxxx>, Andrew Cooper <andrew.cooper3@xxxxxxxxxx>, Wei Liu <wei.liu2@xxxxxxxxxx>, Roger Pau Monne <roger.pau@xxxxxxxxxx>
- Delivery-date: Fri, 05 Apr 2019 10:30:18 +0000
- List-id: Xen developer discussion <xen-devel.lists.xenproject.org>
- Openpgp: preference=signencrypt
On 3/13/19 12:38 PM, Jan Beulich wrote:
> In a few cases only a query is intended, i.e. without populating a
> possible PoD or paged out entry, when the intention is to replace the
> current entry anyway. Use get_gfn_query() there instead.
>
> Signed-off-by: Jan Beulich <jbeulich@xxxxxxxx>
The first one should be fine, but pretty sure the second two will
mis-fire for PoD: p2m->pod.entry_count won't get updated. As it is,
it's sort-of misfiring already, since the "freed" memory won't be
reclaimed for the PoD cache.
Which probably means it's time for some serious refactoring to prevent
this sort of error from creeping in. p2m->pod.entry_count accounting
should probably be moved into p2m_entry_modify(), and
p2m_pod_decrease_reservation() should probably be moved somewhere else
-- perhaps guest_remove_page() or something? At any rate, a we probably
need to review of the layers and what everyone needs from them, and do
things at the right level.
-George
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