Re: [Qemu-devel] [PATCH 1/1] xen-hvm.c: Add support for Xen access to vmport

[Don Slutz]

On 09/29/14 06:25, Stefano Stabellini wrote:
> On Mon, 29 Sep 2014, Stefano Stabellini wrote:
> > On Fri, 26 Sep 2014, Don Slutz wrote:
> > > This adds synchronisation of the vcpu registers
> > > between Xen and QEMU.
> > >
> > > Signed-off-by: Don Slutz <address@hidden>
> > [...]
> >
> > > diff --git a/xen-hvm.c b/xen-hvm.c
> > > index 05e522c..e1274bb 100644
> > > --- a/xen-hvm.c
> > > +++ b/xen-hvm.c
> > > @@ -857,14 +857,48 @@ static void cpu_handle_ioreq(void *opaque)
> > >   
> > >       handle_buffered_iopage(state);
> > >       if (req) {
> > > +#ifdef IOREQ_TYPE_VMWARE_PORT
> > Is there any reason to #ifdef this code?
> > Couldn't we just always build it in QEMU?

This allows QEMU 2.2 (or later) to build on a system that has Xen 4.5
or earlier installed; and work.

> > > +        if (req->type == IOREQ_TYPE_VMWARE_PORT) {
> > I think it would make more sense to check for IOREQ_TYPE_VMWARE_PORT
> > from within handle_ioreq.

Ok, I can move it.


> > > +            CPUX86State *env;
> > > +            ioreq_t fake_req = {
> > > +                .type = IOREQ_TYPE_PIO,
> > > +                .addr = (uint16_t)req->size,
> > > +                .size = 4,
> > > +                .dir = IOREQ_READ,
> > > +                .df = 0,
> > > +                .data_is_ptr = 0,
> > > +            };
> Why do you need a fake req?

To transport the 6 VCPU registers (only 32bits of them) that vmport.c
needs to do it's work.

> Couldn't Xen send the real req instead?

Yes, but then a 2nd exchange between QEMU and Xen would be needed
to fetch the 6 VCPU registers.  The ways I know of to fetch the VCPU 
registers from Xen, all need many cycles to do their work and return
a lot of data that is not needed.

The other option that I have considered was to extend the ioreq_t type
to have room for these registers, but that reduces by almost half the
maximum number of VCPUs that are supported (They all live on 1 page).

>   If any case you should spend a
> few more words on why you are doing this.

Sure.  Will add some form of the above as part of the commit message.

> > > +            if (!xen_opaque_env) {
> > > +                xen_opaque_env = g_malloc(sizeof(CPUX86State));
> > > +            }
> > > +            env = xen_opaque_env;
> > > +            env->regs[R_EAX] = (uint32_t)(req->addr >> 32);
> > > +            env->regs[R_EBX] = (uint32_t)(req->addr);
> > > +            env->regs[R_ECX] = req->count;
> > > +            env->regs[R_EDX] = req->size;
> > > +            env->regs[R_ESI] = (uint32_t)(req->data >> 32);
> > > +            env->regs[R_EDI] = (uint32_t)(req->data);
> > > +            handle_ioreq(&fake_req);
> > > +            req->addr = ((uint64_t)fake_req.data << 32) |
> > > +                (uint32_t)env->regs[R_EBX];
> > > +            req->count = env->regs[R_ECX];
> > > +            req->size = env->regs[R_EDX];
> > > +            req->data = ((uint64_t)env->regs[R_ESI] << 32) |
> > > +                (uint32_t)env->regs[R_EDI];
> > This code could be moved to a separate helper function called by
> > handle_ioreq.

Ok.

   -Don Slutz

> > > +        } else {
> > > +            handle_ioreq(req);
> > > +        }
> > > +#else
> > >           handle_ioreq(req);
> > > +#endif