[Qemu-devel] Re: [PATCH 4/5] Make MMIO address page aligned in guest.

[Gleb Natapov]

On Sun, Oct 11, 2009 at 11:48:20PM +0200, Michael S. Tsirkin wrote:
> On Sun, Oct 11, 2009 at 08:59:06PM +0200, Gleb Natapov wrote:
> > MMIO of some devices are not page aligned, such as some EHCI
> > controllers and virtual Realtek NIC in guest. Current guest
> > bios doesn't guarantee the start address of MMIO page aligned.
> > This may result in failure of device assignment, because KVM
> > only allow to register page aligned memory slots. For example,
> > it fails to assign EHCI controller (its MMIO size is 1KB) with
> > virtual Realtek NIC (its MMIO size is 256Bytes), because MMIO
> > of virtual Realtek NIC in guest starts from 0xf2001000, MMIO of
> > the EHCI controller will starts from 0xf2001400.
> > 
> > MMIO addresses in guest are allocated in guest bios. This patch
> > makes MMIO address page aligned in bios, then fixes the issue.
> > 
> > qemu-kvm commit ccc9b91a1fdfac4161461a519e10a233f5066d2f
> > 
> > Signed-off-by: Gleb Natapov <address@hidden>
> 
> This wastes memory for non-assigned devices.  I think it's better, and
> cleaner, to make qemu increase the BAR size up to 4K for assigned
> devices if it wants page size alignment.
> 
We have three and a half devices in QEUM so I don't think memory is a
big concern. Regardless, if you think that fiddle with assigned devices
responses is better idea go ahead and send patches. As it stands this
patch is in kvm's bios and is required for assigned devices to work
for some devices, so moving to seabios without this patch will introduce
a regression.

> 
> > ---
> >  src/pciinit.c |    7 +++++++
> >  1 files changed, 7 insertions(+), 0 deletions(-)
> > 
> > diff --git a/src/pciinit.c b/src/pciinit.c
> > index 29b3901..53fbfcf 100644
> > --- a/src/pciinit.c
> > +++ b/src/pciinit.c
> > @@ -10,6 +10,7 @@
> >  #include "biosvar.h" // GET_EBDA
> >  #include "pci_ids.h" // PCI_VENDOR_ID_INTEL
> >  #include "pci_regs.h" // PCI_COMMAND
> > +#include "paravirt.h"
> >  
> >  #define PCI_ROM_SLOT 6
> >  #define PCI_NUM_REGIONS 7
> > @@ -158,6 +159,12 @@ static void pci_bios_init_device(u16 bdf)
> >                  *paddr = ALIGN(*paddr, size);
> >                  pci_set_io_region_addr(bdf, i, *paddr);
> >                  *paddr += size;
> > +                if (kvm_para_available()) {
> > +                    /* make memory address page aligned */
> > +                    /* needed for device assignment on kvm */
> > +                    if (!(val & PCI_BASE_ADDRESS_SPACE_IO))
> > +                        *paddr = (*paddr + 0xfff) & 0xfffff000;
> > +               }
> >              }
> >          }
> >          break;
> > -- 
> > 1.6.3.3
> > 
> > 

--
                        Gleb.