Re: [Xen-devel] [PATCH v6 02/11] vpci: introduce basic handlers to trap accesses to the PCI config space

[Roger Pau Monné <roger.pau@xxxxxxxxxx>]

On Wed, Oct 04, 2017 at 09:54:18AM +0000, Jan Beulich wrote:
> >>> On 04.10.17 at 11:24, <roger.pau@xxxxxxxxxx> wrote:
> > On Wed, Oct 04, 2017 at 08:30:38AM +0000, Jan Beulich wrote:
> >> >>> On 19.09.17 at 17:29, <roger.pau@xxxxxxxxxx> wrote:
> >> > +static int vpci_portio_read(const struct hvm_io_handler *handler,
> >> > +                            uint64_t addr, uint32_t size, uint64_t 
> >> > *data)
> >> > +{
> >> > +    struct domain *d = current->domain;
> >> > +    unsigned int reg;
> >> > +    pci_sbdf_t sbdf;
> >> > +    uint32_t cf8;
> >> > +
> >> > +    *data = ~(uint64_t)0;
> >> > +
> >> > +    if ( addr == 0xcf8 )
> >> > +    {
> >> > +        ASSERT(size == 4);
> >> > +        *data = d->arch.hvm_domain.pci_cf8;
> >> > +        return X86EMUL_OKAY;
> >> > +    }
> >> > +
> >> > +    cf8 = ACCESS_ONCE(d->arch.hvm_domain.pci_cf8);
> >> > +    if ( !CF8_ENABLED(cf8) )
> >> > +        return X86EMUL_OKAY;
> >> 
> >> Why is this OKAY instead of UNHANDLEABLE? The access is supposed to be
> >> forwarded to qemu if it's not a config space one. Same in the write path
> >> then.
> > 
> > No, I don't think this should be forwarded to QEMU. It is a config
> > space access (because vpci_portio_accept returned true). But the value
> > in CF8 doesn't have the enabled bit set, hence the access is
> > discarded.
> 
> With the enable bit clear it is my understanding that this is then
> _not_ a config space access. vpci_portio_accept() simply doesn't
> have enough information to tell.

OK, it was my understanding that accesses to cf8/cfc where only used
by the PCI config space.

Roger.

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