Re: [Qemu-devel] [PATCH v2] vfio: Filter out bogus mappings

[Michael S. Tsirkin]

On Wed, Jan 15, 2014 at 09:44:14PM -0700, Alex Williamson wrote:
> Since 57271d63 we now see spurious mappings with the upper bits set
> if 64bit PCI BARs are sized while enabled.  The guest writes a mask
> of 0xffffffff to the lower BAR to size it, then restores it, then
> writes the same mask to the upper BAR resulting in a spurious BAR
> mapping into the last 4G of the 64bit address space.  Most
> architectures do not support or make use of the full 64bits address
> space for PCI BARs, so we filter out mappings with the high bit set.
> Long term, we probably need to think about vfio telling us the
> address width limitations of the IOMMU.
> 
> Signed-off-by: Alex Williamson <address@hidden>

Reviewed-by: Michael S. Tsirkin <address@hidden>

Did you say something similar is needed for legacy
assigned devices as well?

> ---
>  hw/misc/vfio.c |    9 ++++++++-
>  1 file changed, 8 insertions(+), 1 deletion(-)
> 
> diff --git a/hw/misc/vfio.c b/hw/misc/vfio.c
> index 30b1a78..d304213 100644
> --- a/hw/misc/vfio.c
> +++ b/hw/misc/vfio.c
> @@ -2156,7 +2156,14 @@ static int vfio_dma_map(VFIOContainer *container, 
> hwaddr iova,
>  
>  static bool vfio_listener_skipped_section(MemoryRegionSection *section)
>  {
> -    return !memory_region_is_ram(section->mr);
> +    return !memory_region_is_ram(section->mr) ||
> +           /*
> +            * Sizing an enabled 64-bit BAR can cause spurious mappings to
> +            * addresses in the upper part of the 64-bit address space.  These
> +            * are never accessed by the CPU and beyond the address width of
> +            * some IOMMU hardware.  TODO: VFIO should tell us the IOMMU 
> width.
> +            */
> +           section->offset_within_address_space & (1ULL << 63);
>  }
>  
>  static void vfio_listener_region_add(MemoryListener *listener,