Re: [Qemu-devel] [PATCH] pci: Add generic PCI device option to disable 64bit MMIO BARs

[Alex Williamson]

On Thu, 2012-02-02 at 01:14 +0200, Michael S. Tsirkin wrote:
> On Wed, Feb 01, 2012 at 03:57:02PM -0700, Alex Williamson wrote:
> > As we start to enable 64bit I/O devices, there's a good chance
> > we'll find bugs and compatibility issues.  This allows a user
> > to toggle off (default on) 64bit PCI MMIO BARs, downgrading
> > them to 32bit BARs.
> > 
> > Signed-off-by: Alex Williamson <address@hidden>
> > ---
> > 
> > Should this be an "x-mem64" option implying that it's really
> > only for debugging and may go away or could this have some
> > longevity?
> 
> I'd rename it x-force_32bit, for clarify.
> Can this go into assigned devices?
> Then the error handling below won't be a problem.

That was kinda the point of putting it in common code so we don't end up
with pci-assign.mem64 vs ivshmem.dontuse64bitbars vs
virtio-net-pci.heyonlyuse32bitbars.  Do we think there's zero chance
that other drivers will want this?

> >  hw/pci.c |   18 ++++++++++++++++++
> >  hw/pci.h |    4 ++++
> >  2 files changed, 22 insertions(+), 0 deletions(-)
> > 
> > diff --git a/hw/pci.c b/hw/pci.c
> > index 57ec104..9afddb0 100644
> > --- a/hw/pci.c
> > +++ b/hw/pci.c
> > @@ -63,6 +63,8 @@ struct BusInfo pci_bus_info = {
> >                          QEMU_PCI_CAP_MULTIFUNCTION_BITNR, false),
> >          DEFINE_PROP_BIT("command_serr_enable", PCIDevice, cap_present,
> >                          QEMU_PCI_CAP_SERR_BITNR, true),
> > +        DEFINE_PROP_BIT("mem64", PCIDevice, cap_present,
> > +                        QEMU_PCI_CAP_MEM64_BITNR, true),
> >          DEFINE_PROP_END_OF_LIST()
> >      }
> >  };
> > @@ -957,6 +959,22 @@ void pci_register_bar(PCIDevice *pci_dev, int 
> > region_num,
> >          exit(1);
> >      }
> >  
> > +    if (!(type & PCI_BASE_ADDRESS_SPACE_IO)) {
> > +        if (!(pci_dev->cap_present & QEMU_PCI_CAP_MEM64)) {
> > +            type &= ~PCI_BASE_ADDRESS_MEM_TYPE_64;
> > +        }
> > +
> > +        /* 32bit BARs are limited to 2GB */
> > +        if (size >= 0x80000000U && !(type & PCI_BASE_ADDRESS_MEM_TYPE_64)) 
> > {
> > +            fprintf(stderr, "Device %04x:%02x:%02x.%x BAR %d is %ld "
> > +                    "GB, 64bit memory type required\n",
> > +                    pci_find_domain(pci_dev->bus), 
> > pci_bus_num(pci_dev->bus),
> > +                    PCI_SLOT(pci_dev->devfn), PCI_FUNC(pci_dev->devfn),
> > +                    region_num, (long)(size >> 30));
> > +            exit(1);
> 
> That's an unfriendly way to handle errors, especially
> for hotplug.  If you move the option to device itself,
> then it can just fail init.

It's unfriendly that we have so many void functions so we can't return a
proper error.  Hitting this error is so incredibly unlikely that I don't
think it deserves some grand rework...

> errors should also go to the monitor nowdays, so no fprintf.

Ok.

> > +        }
> > +    }
> > +
> >      r = &pci_dev->io_regions[region_num];
> >      r->addr = PCI_BAR_UNMAPPED;
> >      r->size = size;
> > diff --git a/hw/pci.h b/hw/pci.h
> > index 4220151..17fd996 100644
> > --- a/hw/pci.h
> > +++ b/hw/pci.h
> > @@ -126,6 +126,10 @@ enum {
> >      /* command register SERR bit enabled */
> >  #define QEMU_PCI_CAP_SERR_BITNR 4
> >      QEMU_PCI_CAP_SERR = (1 << QEMU_PCI_CAP_SERR_BITNR),
> > +
> > +    /* expose 64bit MMIO BARs when available */
> > +#define QEMU_PCI_CAP_MEM64_BITNR 5
> > +    QEMU_PCI_CAP_MEM64 = (1 << QEMU_PCI_CAP_MEM64_BITNR),
> >  };
> >  
> >  typedef int (*msix_mask_notifier_func)(PCIDevice *, unsigned vector,