Re: [Qemu-devel] [PATCH] vfio/pci: Hide SR-IOV capability

[Alex Williamson <alex.williamson@redhat.com>]

On Mon, 20 Jun 2016 16:23:07 -0600
Eric Blake <eblake@redhat.com> wrote:

> On 06/20/2016 04:04 PM, Alex Williamson wrote:
> > The kernel currently exposes the SR-IOV capability as read-only
> > through vfio-pci.  This is sufficient to protect the host kernel, but
> > has the potential to confuse guests without further virtualization.
> > In particular, OVMF tries to size the VF BARs and comes up with absurd
> > results, ending with an assert.  There's not much point in adding
> > virtualization to a read-only capability, so we simply hide it for
> > now.  If the kernel ever enables SR-IOV virtualization, we should
> > easily be able to test it through VF BAR sizing or explicit flags.
> > 
> > Testing whether we should parse extended capabilities is also pulled
> > into the function to keep these assumptions in one place.
> > 
> > Signed-off-by: Alex Williamson <alex.williamson@redhat.com>
> > ---  
> 
> > +     * Extended capabilities are chained with each pointing to the next, so we
> > +     * can drop anything other than the head of the chain simply by modifying
> > +     * the previous next pointer.  For the head of the chain, we can modify the
> > +     * capability ID to something that cannot match a valid capability.  ID
> > +     * 0 is reserved for this since absence of capabilities is indicated by
> > +     * 0 for the ID, version, AND next pointer.  However, pcie_add_capability()
> > +     * uses ID 0 as reserved for list management and will incorrectly match and
> > +     * assert if we attempt to pre-load the head of the chain with with this
> > +     * ID.  Use ID 0xFFFF temporarily since it is also seems to be reserved in
> > +     * part for identifying abscense of capabilities in a root complex register  
> 
> s/abscense/absence/
> 

Thanks, updated:

diff --git a/hw/vfio/pci.c b/hw/vfio/pci.c
index 36d5e00..2418b93 100644
--- a/hw/vfio/pci.c
+++ b/hw/vfio/pci.c
@@ -1796,7 +1796,7 @@ static int vfio_add_ext_cap(VFIOPCIDevice *vdev)
      * uses ID 0 as reserved for list management and will incorrectly match and
      * assert if we attempt to pre-load the head of the chain with with this
      * ID.  Use ID 0xFFFF temporarily since it is also seems to be reserved in
-     * part for identifying abscense of capabilities in a root complex register
+     * part for identifying absence of capabilities in a root complex register
      * block.  If the ID still exists after adding capabilities, switch back to
      * zero.  We'll mark this entire first dword as emulated for this purpose.
      */