Re: [Qemu-devel] [PATCH] kernel vfio: PCI ROM size calculation

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

On Mon, 2012-05-14 at 13:24 +1000, Alexey Kardashevskiy wrote:
> On 14/05/12 12:55, Alex Williamson wrote:
> > On Sat, 2012-05-12 at 16:50 +1000, Alexey Kardashevskiy wrote:
> >> The original code calculated the real size of the ROM and passed it to
> >> QEMU which tried to do pci_register_bar and failed with error message
> >> "ERROR: PCI region size must be pow2".
> >>
> >> The example card is PCIe Intel E1000E with the ROM size 0x9c00.
> >>
> >> pci_resource_len seems to be a proper solution.
> >>
> >> Signed-off-by: Alexey Kardashevskiy <aik@ozlabs.ru>
> >> ---
> >>  drivers/vfio/pci/vfio_pci.c |    9 +++------
> >>  1 files changed, 3 insertions(+), 6 deletions(-)
> >>
> >> diff --git a/drivers/vfio/pci/vfio_pci.c b/drivers/vfio/pci/vfio_pci.c
> >> index b2f1f3a..6d4a783 100644
> >> --- a/drivers/vfio/pci/vfio_pci.c
> >> +++ b/drivers/vfio/pci/vfio_pci.c
> >> @@ -234,12 +234,9 @@ static long vfio_pci_ioctl(void *device_data,
> >>  			 * this gives the user an easy way to determine whether
> >>  			 * there's anything here w/o trying to read it. */
> > 
> > This is actually intentional, but maybe isn't the best way to handle it
> > anymore.  The cut-off comment above reads:
> > 
> >         /* Report the actual ROM size instead of the BAR size,
> >          * this gives the user an easy way to determine whether
> >          * there's anything here w/o trying to read it. */
> > 
> > At the time I added that though, I think we still had a separate ioctl
> > to get the BAR size, so one gave the real size, the other the BAR size.
> > Do we care to expose that ROMs have real size, maybe zero, that doesn't
> > necessarily match pci_resource_len()?  Thanks,
> 
> 
> The guest will still see aligned ROM BAR (not real one) and may try to read behind the real end of
> ROM, and it is allowed while it is still within the BAR, right?

Yes.

> >>  			if (info.index == VFIO_PCI_ROM_REGION_INDEX) {
> >> -				void __iomem *io;
> >> -				size_t size;
> >> -
> >> -				io = pci_map_rom(pdev, &size);
> >> -				info.size = io ? size : 0;
> >> -				pci_unmap_rom(pdev, io);
> >> +				info.size = pci_resource_len(pdev,
> >> +						PCI_ROM_RESOURCE);
> >> +				info.flags |= VFIO_PCI_ROM_REGION_INDEX;
> >>  			} else if (flags & IORESOURCE_MEM) {
> >>  				info.size = pci_resource_len(pdev, info.index);
> >>  				info.flags |= (VFIO_REGION_INFO_FLAG_WRITE |
> >>
> > 
> > 
> > 
> 
>