Re: [Xen-devel] [PATCH v7 11/12] x86/hvm/ioreq: defer mapping gfns until they are actually requsted

[Paul Durrant <Paul.Durrant@xxxxxxxxxx>]

> -----Original Message-----
> From: Jan Beulich [mailto:JBeulich@xxxxxxxx]
> Sent: 25 September 2017 17:00
> To: Paul Durrant <Paul.Durrant@xxxxxxxxxx>
> Cc: Andrew Cooper <Andrew.Cooper3@xxxxxxxxxx>; George Dunlap
> <George.Dunlap@xxxxxxxxxx>; Ian Jackson <Ian.Jackson@xxxxxxxxxx>;
> Stefano Stabellini <sstabellini@xxxxxxxxxx>; xen-devel@xxxxxxxxxxxxxxxxxxxx;
> Konrad Rzeszutek Wilk <konrad.wilk@xxxxxxxxxx>; Tim (Xen.org)
> <tim@xxxxxxx>
> Subject: Re: [PATCH v7 11/12] x86/hvm/ioreq: defer mapping gfns until they
> are actually requsted
> 
> >>> On 18.09.17 at 17:31, <paul.durrant@xxxxxxxxxx> wrote:
> > --- a/xen/arch/x86/hvm/ioreq.c
> > +++ b/xen/arch/x86/hvm/ioreq.c
> > @@ -354,6 +354,9 @@ static void hvm_update_ioreq_evtchn(struct
> hvm_ioreq_server *s,
> >      }
> >  }
> >
> > +#define HANDLE_BUFIOREQ(s) \
> > +    (s->bufioreq_handling != HVM_IOREQSRV_BUFIOREQ_OFF)
> 
> (s)
> 
> > @@ -762,11 +755,20 @@ int hvm_get_ioreq_server_info(struct domain
> *d, ioservid_t id,
> >      if ( IS_DEFAULT(s) )
> >          goto out;
> >
> > +    if ( ioreq_gfn || bufioreq_gfn )
> 
> This conditional together with ...
> 
> > +    {
> > +        rc = hvm_ioreq_server_map_pages(s);
> > +        if ( rc )
> > +            goto out;
> > +    }
> > +
> >      *ioreq_gfn = gfn_x(s->ioreq.gfn);
> 
> ... this unconditional dereference is suspicious.

True, it should be protected.

> 
> > --- a/xen/include/asm-x86/hvm/domain.h
> > +++ b/xen/include/asm-x86/hvm/domain.h
> > @@ -68,8 +68,8 @@ struct hvm_ioreq_server {
> >      spinlock_t             bufioreq_lock;
> >      evtchn_port_t          bufioreq_evtchn;
> >      struct rangeset        *range[NR_IO_RANGE_TYPES];
> > +    int                    bufioreq_handling;
> 
> Does this need to be plain int (i.e. signed and 32 bits wide)?

No, I can shrink it.

  Paul

> 
> Jan


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