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

[Yu Zhang <yu.c.zhang@xxxxxxxxxxxxxxx>]

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"?

> > @@ -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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