Re: [Qemu-devel] [PATCH] pci: Error on PCI capability collisions

["Michael S. Tsirkin" <mst@redhat.com>]

On Tue, Aug 23, 2011 at 12:21:47PM -0600, Alex Williamson wrote:
> On Tue, 2011-08-23 at 21:17 +0300, Michael S. Tsirkin wrote:
> > On Tue, Aug 23, 2011 at 07:28:08PM +0200, Jan Kiszka wrote:
> > > From: Alex Williamson <alex.williamson@redhat.com>
> > > 
> > > Nothing good can happen when we overlap capabilities
> > > 
> > > [ Jan: rebased over qemu, minor formatting ]
> > > 
> > > Signed-off-by: Jan Kiszka <jan.kiszka@siemens.com>
> > 
> > I'll stick an assert there instead. Normal devices
> > don't generate overlapping caps unless there's a bug,
> > and device assignment should do it's own checks.
> > 
> > I really have a mind to rip out the used array too.
> 
> So you'd rather kill qemu rather than have a reasonable error return
> path... great :(
> 
> Alex

Well that will make it possible to make pci_add_capability return void,
less work for callers :) Dev assignment is really the only place where
capability offsets need to be verified.

> > > ---
> > >  hw/pci.c |   14 ++++++++++++++
> > >  1 files changed, 14 insertions(+), 0 deletions(-)
> > > 
> > > diff --git a/hw/pci.c b/hw/pci.c
> > > index 6124790..ff20631 100644
> > > --- a/hw/pci.c
> > > +++ b/hw/pci.c
> > > @@ -1952,11 +1952,25 @@ int pci_add_capability(PCIDevice *pdev, uint8_t cap_id,
> > >                         uint8_t offset, uint8_t size)
> > >  {
> > >      uint8_t *config;
> > > +    int i;
> > > +
> > >      if (!offset) {
> > >          offset = pci_find_space(pdev, size);
> > >          if (!offset) {
> > >              return -ENOSPC;
> > >          }
> > > +    } else {
> > > +        for (i = offset; i < offset + size; i++) {
> > > +            if (pdev->used[i]) {
> > > +                fprintf(stderr, "ERROR: %04x:%02x:%02x.%x "
> > > +                        "Attempt to add PCI capability %x at offset "
> > > +                        "%x overlaps existing capability %x at offset %x\n",
> > > +                        pci_find_domain(pdev->bus), pci_bus_num(pdev->bus),
> > > +                        PCI_SLOT(pdev->devfn), PCI_FUNC(pdev->devfn),
> > > +                        cap_id, offset, pdev->config_map[i], i);
> > > +                return -EFAULT;
> > > +            }
> > > +        }
> > >      }
> > >  
> > >      config = pdev->config + offset;
> > > -- 
> > > 1.7.3.4
> 
>