Re: [PATCH 05/15] xen: p2m: new 'p2m_epc' type for EPC mapping

["Huang, Kai" <kai.huang@linux.intel.com>]

On 7/13/2017 12:21 AM, George Dunlap wrote:
> 
>> On Jul 12, 2017, at 1:01 PM, Andrew Cooper <andrew.cooper3@citrix.com> wrote:
>>
>> On 09/07/17 10:12, Kai Huang wrote:
>>> A new 'p2m_epc' type is added for EPC mapping type. Two wrapper functions
>>> set_epc_p2m_entry and clear_epc_p2m_entry are also added for further use.
>>
>> Other groups in Intel have been looking to reduce the number of p2m types we have, so we can use more hardware defined bits in the EPT pagetable entries.
>>
>> If we need a new type then we will certainly add one, but it is not clear why this type is needed.
> 
> Does the hypervisor need to know which pages of a domain’s p2m 1) have valid config set up, but 2) aren’t accessible to itself or any other domain?

Hi Andrew, George,

Actually I haven't thought this thoroughly, but my first glance is 
there's no existing p2m_type that can be reasonably used for EPC. 
Probably p2m_ram_rw or p2m_mmio_direct are two potential candidates. For 
EPC, for *static partitioning* Xen hypervisor just needs to setup 
mappings and then leave it until guest is destroyed. But for p2m_ram_rw 
and p2m_mmio_direct there are additional logic when Xen learns about the 
two types. To me adding 'p2m_epc' is more straightforward and safe. 
Maybe we can change to a more generic name such as 'p2m_ram_encrypted'? 
But again I am not sure other encryption technology can also be applied 
to EPC.

> 
>   -George
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