Re: [Xen-devel] [PATCH v7 3/5] x86/ioreq server: Handle read-modify-write cases for p2m_ioreq_server pages.

["Jan Beulich" <JBeulich@xxxxxxxx>]

>>> On 11.03.17 at 09:42, <yu.c.zhang@xxxxxxxxxxxxxxx> wrote:
> On 3/10/2017 11:33 PM, Jan Beulich wrote:
>>>>> On 08.03.17 at 16:33, <yu.c.zhang@xxxxxxxxxxxxxxx> wrote:
>>> @@ -197,6 +217,10 @@ static int hvmemul_do_io(
>>>            *   - If the IOREQ_MEM_ACCESS_WRITE flag is not set, treat it
>>>            *   like a normal PIO or MMIO that doesn't have an ioreq
>>>            *   server (i.e., by ignoring it).
>>> +         *
>>> +         *   - If the accesss is a read, this could be part of a
>>> +         *   read-modify-write instruction, emulate the read so that we
>>> +         *   have it.
>> "it" being what here? Grammatically the insn, but we don't care
>> about "having" the insn.
> 
> Here "have it" means " to have the value on this address copied in".
> Sorry for the inaccurate comment. How about just "emulate the read first"?

Sounds okay.

>>> @@ -226,6 +250,17 @@ static int hvmemul_do_io(
>>>                   }
>>>   
>>>                   /*
>>> +                 * This is part of a read-modify-write instruction.
>> "is" or "may be"?
> 
> I believe should be "is".
> It's the only scenario I can imagine when an read operation(only when 
> this operation is
> also a write one) traps. Otherwise there shall be no VM exit.

Even with a racing update to the type?

Jan


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