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

["Michael S. Tsirkin" <mst@redhat.com>]

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 <gleb@redhat.com>

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.


> ---
>  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
> 
>