On 04/03/2013 02:09:45 PM, Stuart Yoder wrote:
> Would is be possible for userspace to simply leave room for MSI bank
> mapping (how much room could be determined by something like
> VFIO_IOMMU_GET_MSI_BANK_COUNT) then document the API that userspace
can
> DMA_MAP starting at the 0x0 address of the aperture, growing up, and
> VFIO will map banks on demand at the top of the aperture, growing
down?
> Wouldn't that avoid a lot of issues with userspace needing to know
> anything about MSI banks (other than count) and coordinating irq
numbers
> and enabling handlers?
This is basically option #A in the original proposals sent. I like
this approach, in that it
is simpler and keeps user space mostly out of this...which is
consistent with how things are done
on x86. User space just needs to know how many windows to leave at
the top of the aperture.
The kernel then has the flexibility to use those windows how it wants.
But one question, is when should the kernel actually map (and unmap)
the MSI banks.
I think userspace should explicitly request it. Userspace still
wouldn't need to know anything but the count:
count = VFIO_IOMMU_GET_MSI_BANK_COUNT
VFIO_IOMMU_SET_ATTR(ATTR_GEOMETRY)
VFIO_IOMMU_SET_ATTR(ATTR_WINDOWS)
// do other DMA maps now, or later, or not at all, doesn't matter
for (i = 0; i < count; i++)
VFIO_IOMMU_MAP_MSI_BANK(iova, i);
// The kernel now knows where each bank has been mapped, and can update
PCI config space appropriately.
One thing we need to do is enable the aperture...and current
thinking is that is done on the first DMA_MAP.
What if there are no other mappings required?
-Scott
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