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

[Yu Zhang <yu.c.zhang@linux.intel.com>]

On 3/10/2017 11:33 PM, Jan Beulich wrote:
>>>> On 08.03.17 at 16:33, <yu.c.zhang@linux.intel.com> 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"?

>> @@ -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.

Thanks
Yu
> Jan
>
>
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