Re: [Xen-devel] [PATCH v4 17/17] x86/hvm: track large memory mapped accesses by buffer offset

[Paul Durrant <Paul.Durrant@xxxxxxxxxx>]

> -----Original Message-----
> From: Paul Durrant
> Sent: 25 June 2015 11:52
> To: 'Jan Beulich'
> Cc: Andrew Cooper; xen-devel@xxxxxxxxxxxxxxxxxxxx; Keir (Xen.org)
> Subject: RE: [PATCH v4 17/17] x86/hvm: track large memory mapped
> accesses by buffer offset
> 
> > -----Original Message-----
> > From: Jan Beulich [mailto:JBeulich@xxxxxxxx]
> > Sent: 25 June 2015 11:47
> > To: Paul Durrant
> > Cc: Andrew Cooper; xen-devel@xxxxxxxxxxxxxxxxxxxx; Keir (Xen.org)
> > Subject: Re: [PATCH v4 17/17] x86/hvm: track large memory mapped
> > accesses by buffer offset
> >
> > >>> On 24.06.15 at 13:24, <paul.durrant@xxxxxxxxxx> wrote:
> > > @@ -621,14 +574,41 @@ static int hvmemul_phys_mmio_access(
> > >
> > >      for ( ;; )
> > >      {
> > > -        rc = hvmemul_do_mmio_buffer(gpa, &one_rep, chunk, dir, 0,
> > > -                                    *buffer);
> > > -        if ( rc != X86EMUL_OKAY )
> > > -            break;
> > > +        /* Have we already done this chunk? */
> > > +        if ( (*off + chunk) <= vio->mmio_cache[dir].size )
> >
> > I can see why you would like to get rid of the address check, but
> > I'm afraid you can't: You have to avoid getting mixed up multiple
> > same kind (reads or writes) memory accesses that a single
> > instruction can do. While generally I would assume that
> > secondary accesses (like the I/O bitmap read associated with an
> > OUTS) wouldn't go to MMIO, CMPS with both operands being
> > in MMIO would break even if neither crosses a page boundary
> > (not to think of when the emulator starts supporting the
> > scatter/gather instructions, albeit supporting them will require
> > further changes, or we could choose to do them one element at
> > a time).
> 
> Ok. Can I assume at most two distinct set of addresses for read or write? If 
> so
> then I can just keep two sets of caches in the hvm_io struct.
> 

Oh, I mean linear addresses here BTW.

  Paul

> >
> > > +        {
> > > +            ASSERT(*off + chunk <= vio->mmio_cache[dir].size);
> >
> > I don't see any difference to the if() expression just above.
> >
> 
> That's possible  - this has been through a few re-bases.
> 
> > > +            if ( dir == IOREQ_READ )
> > > +                memcpy(&buffer[*off],
> > > +                       &vio->mmio_cache[IOREQ_READ].buffer[*off],
> > > +                       chunk);
> > > +            else
> > > +            {
> > > +                if ( memcmp(&buffer[*off],
> >
> > "else if" please.
> >
> 
> Ok.
> 
> > > +                            &vio->mmio_cache[IOREQ_WRITE].buffer[*off],
> > > +                            chunk) != 0 )
> > > +                    domain_crash(curr->domain);
> > > +            }
> > > +        }
> > > +        else
> > > +        {
> > > +            ASSERT(*off == vio->mmio_cache[dir].size);
> > > +
> > > +            rc = hvmemul_do_mmio_buffer(gpa, &one_rep, chunk, dir, 0,
> > > +                                        &buffer[*off]);
> > > +            if ( rc != X86EMUL_OKAY )
> > > +                break;
> > > +
> > > +            /* Note that we have now done this chunk */
> >
> > Missing stop.
> >
> 
> Ok.
> 
>   Paul
> 
> > Jan


_______________________________________________
Xen-devel mailing list
Xen-devel@xxxxxxxxxxxxx
http://lists.xen.org/xen-devel