Re: [Xen-devel] [PATCH 3/3] Add HVMOP to map guest ram with p2m_ioreq_server to an ioreq server

["Jan Beulich" <JBeulich@xxxxxxxx>]

>>> On 22.03.16 at 18:51, <Paul.Durrant@xxxxxxxxxx> wrote:
>> From: George Dunlap [mailto:george.dunlap@xxxxxxxxxx]
>> Sent: 22 March 2016 17:27
>> There's not much documentation in the code about how this is expected to
>> be used.
>> 
>> For instance, having separate flags seems to imply that you can
>> independently select either read intercept, write intercept, or both;
>> but [ept_]p2m_type_to_flags() seems to assume that READ_ACCESS implies
>> WRITE_ACCESS.  Do you plan to implement them separately in the future?
>> If not, would it be better to make the interface an enum instead?
>> 
>> At very least it should be documented that READ_ACCESS implies
>> WRITE_ACCESS.
> 
> That's not true. If WRITE_ACCESS has not been requested then writes are 
> handled directly in Xen rather than being forwarded to the ioreq server. If 
> h/w were to allow pages to be marked write-only then we wouldn't need to do 
> that.

At least on EPT iirc you can have write-only pages, due to there
being both an R and a W bit.

>> > +    p2m_memory_type_changed(d);
>> > +
>> > +    rc = 0;
>> > +
>> > +out:

Btw: label placement.

Jan


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