Re: [Xen-devel] [PATCH v6 03/11] x86/mmcfg: add handlers for the PVH Dom0 MMCFG areas

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

On Wed, Oct 04, 2017 at 08:31:18AM +0000, Jan Beulich wrote:
> >>> On 19.09.17 at 17:29, <roger.pau@xxxxxxxxxx> wrote:
> > +static int vpci_mmcfg_read(struct vcpu *v, unsigned long addr,
> > +                           unsigned int len, unsigned long *data)
> > +{
> > +    struct domain *d = v->domain;
> > +    const struct hvm_mmcfg *mmcfg;
> > +    unsigned int reg;
> > +    pci_sbdf_t sbdf;
> > +
> > +    *data = ~0ul;
> > +
> > +    read_lock(&d->arch.hvm_domain.mmcfg_lock);
> > +    mmcfg = vpci_mmcfg_find(d, addr);
> > +    if ( !mmcfg )
> > +    {
> > +        read_unlock(&d->arch.hvm_domain.mmcfg_lock);
> > +        return X86EMUL_OKAY;
> > +    }
> 
> With the lock dropped between accept() and read() (or write() below),
> is it really appropriate to return OKAY here? The access again should
> be forwarded to qemu, I would think.

That's right, the MCFG area could have been removed in the meantime.
I guess it is indeed more appropriate to return X86EMUL_UNHANDLEABLE
or X86EMUL_RETRY.

It would seem like RETRY is better, since a new call to _accept should
return false now.

Roger.

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