Re: [PATCH] kvm: device-assignment: Add PCI option ROM support

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

On Fri, 2009-06-19 at 15:27 +0800, Yang, Sheng wrote:
> On Friday 19 June 2009 00:28:41 Alex Williamson wrote:
> > The one oddity I noticed is that even when the enable bit is clear, the
> > guest can read the ROM.  I don't know that this is actually illegal, vs
> > returning zeros or ones though.  It seems like maybe the generic PCI
> > code isn't tracking the enable bit.  I think that's an independent
> > problem from this patch though.  Thanks,
> 
> That should be fine. I've taken a look at code, seems Linux kernel set 
> enable_bit when someone begin to read rom, and copy rom to buffer, then unmap 
> the rom. So the rom can be read when enable bit clear.

For this testing, I used an mmap of the ROM address though, so the
kernel caching shouldn't have been involved.  It looks to me like the
problem is that the map function provided via pci_register_io_region()
only knows how to create mappings, not tear them down.  I think maybe
pci_update_mappings() should still call the map_func when new_addr is -1
to let the io space drive shutdown the mapping.  As it is, once we setup
the mapping, it lives until something else happens to overlap it,
regardless of the state of the PCI BAR.  Thanks,

Alex