Re: [PATCH v2 1/9] xen/vpci: introduce basic handlers to trap accesses to the PCI config space

[Paul Durrant <Paul.Durrant@citrix.com>]

> -----Original Message-----
> From: Roger Pau Monne
> Sent: 24 April 2017 10:42
> To: Paul Durrant <Paul.Durrant@citrix.com>
> Cc: xen-devel@lists.xenproject.org; konrad.wilk@oracle.com;
> boris.ostrovsky@oracle.com; Ian Jackson <Ian.Jackson@citrix.com>; Wei Liu
> <wei.liu2@citrix.com>; Jan Beulich <jbeulich@suse.com>; Andrew Cooper
> <Andrew.Cooper3@citrix.com>
> Subject: Re: [PATCH v2 1/9] xen/vpci: introduce basic handlers to trap
> accesses to the PCI config space
> 
> On Fri, Apr 21, 2017 at 05:23:34PM +0100, Paul Durrant wrote:
> > > -----Original Message-----
> > > From: Roger Pau Monne [mailto:roger.pau@citrix.com]
> [...]
> > > +int xen_vpci_read(unsigned int seg, unsigned int bus, unsigned int
> devfn,
> > > +                  unsigned int reg, uint32_t size, uint32_t *data)
> > > +{
> > > +    struct domain *d = current->domain;
> > > +    struct pci_dev *pdev;
> > > +    const struct vpci_register *r;
> > > +    union vpci_val val = { .double_word = 0 };
> > > +    unsigned int data_rshift = 0, data_lshift = 0, data_size;
> > > +    uint32_t tmp_data;
> > > +    int rc;
> > > +
> > > +    ASSERT(vpci_locked(d));
> > > +
> > > +    *data = 0;
> > > +
> > > +    /* Find the PCI dev matching the address. */
> > > +    pdev = pci_get_pdev_by_domain(d, seg, bus, devfn);
> > > +    if ( !pdev )
> > > +        goto passthrough;
> >
> > I hope this can eventually be generalised so I wonder what your intention is
> regarding co-existence between Xen emulated PCI config space, pass-
> through and PCI devices emulated externally. We already have a framework
> for registering PCI devices by SBDF but this code seems to make no use of it,
> which I suspect is likely to cause future conflict.
> 
> Yes, the long term aim is to use this code in order to implement
> PCI-passthrough for PVH and HVM DomUs also.
> 
> TBH, I didn't know we already had such code (I assume you mean the IOREQ
> related PCI code). As it is, I see a couple of issues with that, the first one
> is that this code expects a ioreq client on the other end, and the code I'm
> adding here is all inside of the hypervisor. The second issue is that the IOREQ
> code ATM only allows for local PCI accesses, which means I should extend it
> to
> also deal with ECAM/MMCFG areas.
> 
> I completely agree that at some point this should be made to work together,
> but
> I'm not sure if it would be better to do that once we want to also use vPCI for
> DomUs, so that the Dom0 side is not delayed further.
> 

If the follow up work will definitely be done, then I can live with that. Is there an actual plan to deal with domU pass-through on some backlog somewhere?

  Paul

> Roger.


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