Re: [PATCH RFC] xen: prevent PVH Dom0 from having pages with more than one ref

[Andrew Cooper <andrew.cooper3@citrix.com>]

On 13/06/14 12:05, Jan Beulich wrote:
>>>> Roger Pau Monné<roger.pau@citrix.com> 06/13/14 12:17 PM >>>
>> AFAICT (given my little knowledge about the domain builder), those pages
>> have been allocated by alloc_domheap_pages earlier in the code, which
>> makes them already have 1 ref, and then this loop adds another ref to
>> them, which makes no sense to me.
> alloc_domheap_pages() (or really assign_pages()) takes one reference for
> setting PGC_allocated. This is the reference that gets dropped when freeing
> the page. The code you modify takes a second reference for the usage type
> of the page becoming writable, which is a result of it getting a writable page
> table entry made for it. That reference gets dropped when the respective
> page table entry gets cleared.

Ah, so it is a genuine difference between PV and HVM memory management.

Perhaps the conditional should be based on paging_mode_translate() ?

~Andrew

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