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

["Yang, Sheng" <sheng.yang@intel.com>]

On Friday 19 June 2009 21:44:40 Alex Williamson wrote:
> 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,

I think it may not necessary to tear them down, for the bar mapping won't 
change IIUR.

And you are accessing the sysfs file, right? In the Linux kernel, IIRC, 
pci_create_sysfs_dev_files() create sysfs file, and hook the read to 
pci_read_rom(), which called pci_map_rom(), which would call pci_enable_rom(), 
and write the enable_rom bit to the rom_base_reg. So that the rom can be read 
regardless of enable_rom bit state - and .

But I also found something interested. The write hook of file, pci_write_rom() 
seems won't cause NMI(and seems you need write a char rather than 0 to enable 
the accessing?). So why NMI happen in host?...

-- 
regards
Yang, Sheng