Re: [Xen-devel] [PATCH v1 0/2] Extend ioreq-server to support page write protection

["Jan Beulich" <JBeulich@xxxxxxxx>]

>>> On 05.08.14 at 08:46, <wei.ye@xxxxxxxxx> wrote:
>>  -----Original Message-----
>> From: Jan Beulich [mailto:JBeulich@xxxxxxxx]
>> Sent: Tuesday, August 5, 2014 2:35 PM
>> To: Tian, Kevin
>> Cc: ian.campbell@xxxxxxxxxx; Paul.Durrant@xxxxxxxxxx;
>> ian.jackson@xxxxxxxxxxxxx; stefano.stabellini@xxxxxxxxxxxxx; Ye, Wei; Lv,
>> Zhiyuan; xen-devel@xxxxxxxxxxxxx; keir@xxxxxxx; tim@xxxxxxx 
>> Subject: RE: [PATCH v1 0/2] Extend ioreq-server to support page write
>> protection
>> 
>> >>> On 04.08.14 at 23:34, <kevin.tian@xxxxxxxxx> wrote:
>> > 2nd option, like Wei mentioned in another mail, is to treat such write
>> > protected PPGTT page tables as MMIO. new hypercall is required to
>> > change the p2m type between p2m_io and p2m_ram, based on
>> > allocation/free of guest page table. This way may impact performance
>> > on read though.
>> 
>> Depends on whether you mean mmio_dm or mmio_direct here.
> 
> It's p2m_mmio_dm.

In which case - how would this help? You'd still not be able to deal
with device side accesses. (And as a side note - a hypercall to
convert between p2m_ram_rw and p2m_mmio_dm already exists:
HVMOP_set_mem_type.)

Jan


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