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Re: [Xen-devel] [PATCH v2] xen: prevent PVH Dom0 from having pages with more than one ref

On 13/06/14 13:48, Andrew Cooper wrote:
> On 13/06/14 12:43, Roger Pau Monne wrote:
>> With the current implementation of the Dom0 domain builder a PVH Dom0
>> ends up with pages that have 2 references, which means they are not
>> freed when Dom0 balloons memory down. This leads to those pages
>> not being freed in guest_remove_page, so they are leaked and the
>> memory accounting between Xen and Dom0 differs, because Dom0 OS
>> actually thinks they are freed, but d->tot_pages is not decreased.
> Please can you explain the cause of the problem, and state that it is a
> difference between PV and HVM memory management.

What about the following commit message:

xen: prevent PVH Dom0 from having pages with more than one ref

On PV guests a reference is taken when a page gets added to the page
tables, which makes pages added to the page tables have two references,
but this is not suitable for PVH that doesn't use the PVMMU. In the PVH
case only one reference has to be taken or else the page would not be
freed when the memory of the domain is decreased.


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