Re: [PATCH v4 3/3] x86/ioreq server: Add HVMOP to map guest ram with p2m_ioreq_server to an ioreq server.

From: "Jan Beulich" <JBeulich@suse.com>
To: Yu Zhang <yu.c.zhang@linux.intel.com>
Cc: Kevin Tian <kevin.tian@intel.com>,
	George Dunlap <george.dunlap@eu.citrix.com>,
	Andrew Cooper <andrew.cooper3@citrix.com>,
	Tim Deegan <tim@xen.org>,
	xen-devel@lists.xen.org, Paul Durrant <paul.durrant@citrix.com>,
	zhiyuan.lv@intel.com, Jun Nakajima <jun.nakajima@intel.com>
Subject: Re: [PATCH v4 3/3] x86/ioreq server: Add HVMOP to map guest ram with p2m_ioreq_server to an ioreq server.
Date: Thu, 16 Jun 2016 06:43:02 -0600	[thread overview]
Message-ID: <5762BAF602000078000F5AF8@prv-mh.provo.novell.com> (raw)
In-Reply-To: <57628B0F.8010209@linux.intel.com>

>>> On 16.06.16 at 13:18, <yu.c.zhang@linux.intel.com> wrote:
> On 6/16/2016 6:02 PM, Jan Beulich wrote:
>>>>>>> +struct xen_hvm_map_mem_type_to_ioreq_server {
>>>>>>> +    domid_t domid;      /* IN - domain to be serviced */
>>>>>>> +    ioservid_t id;      /* IN - ioreq server id */
>>>>>>> +    uint16_t type;      /* IN - memory type */
>>>>>>> +    uint16_t pad;
>>>>>> This field does not appear to get checked in the handler.
>>>>> I am now wondering, how about we remove this pad field and define type
>>>>> as uint32_t?
>>>> As above - I think the current layout is fine. But I'm also not heavily
>>>> opposed to using uint32_t here. It's not a stable interface anyway
>>>> (and I already have a series mostly ready to split off all control
>>>> operations from the HVMOP_* ones, into a new HVMCTL_* set,
>>>> which will make all of them interface-versioned).
>>> I'd like to keep this interface. BTW, you mentioned "this field does not
>>> appear to
>>> get checked in the handler", do you mean we need to check the pad in the
>>> handler?
>> Yes.
>>
>>> And why?
>> In order to be able to later assign meaning to it without breaking
>> existing users.
> 
> So the handler need to assure the pad is 0, right?

Correct.

Jan

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