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Feat: IoMmu protocol #1728

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PelleKrab wants to merge 8 commits into rust-osdev:main
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Feat: IoMmu protocol #1728

PelleKrab wants to merge 8 commits into rust-osdev:main from PelleKrab:Iommu

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@PelleKrab PelleKrab commented Jul 21, 2025

This PR adds the IoMmu Protocol to uefi-rs, enabling easy DMA (Direct Memory Access) for devices. This is a draft to get some initial feedback before writing uefi-rs tests. It is already working in my internal project. The main areas I would like feedback on are:

  • Mapping and DMA Buffer Types: Is this too much abstraction? Should we simplify it by requiring the developer to manually call unmap() and free_buffer()?
  • Should free_buffer_raw() and unmap_raw() be made public?
  • Repository Organization: Is the general organization within the repo appropriate?

General Implementation:

// Allocate DMA buffer
let sz = some_buffer.len();
let page_num = bytes_to_pages(sz);
let mut host_buffer = iommu.allocate_buffer(
 MemoryType::BOOT_SERVICES_DATA,
 page_num,
 EdkiiIommuAttribute::MEMORY_CACHED,
)?;
// Map buffer for DMA
let (device_addr, mapping, wrt_size) = iommu.map(
 EdkiiIommuOperation::BUS_MASTER_COMMON_BUFFER,
 &host_buffer,
 size,
)?;
// Give permissions to the specified device 
iommu.set_attribute(some_device_handle, &mapping, EdkiiIommuAccess::READ)?;
// Copy firmware to DMA buffer
let dma_buf = host_buffer.deref_mut();
if sz > wrt_size {
 return Status::BUFFER_TOO_SMALL;
}
dma_buf[..sz].copy_from_slice(&some_buffer[..sz]);
// Notify the Device and pass the `device_addr`

ref:
#1723

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Thanks for working on this :) I haven't had a chance to look at the uefi wrapper in detail yet, but overall it looks reasonable. Could you split the uefi-raw part out to a separate PR? That should be straightforward to review and merge in isolation.
PelleKrab and phip1611 reacted with thumbs up emoji

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Is this ready for review? Currently it's marked as draft still. (No worries if that's intentional, just want to be sure you're not waiting on review.)

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I still need to write some test for it. I have been busy with some other things, so I'll send those over as soon as I can. Feel free to take a look if you want.
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@nicholasbishop I am trying to write some test for this, but I cant seem to get a protocol handle. I went into the uefi shell of the qemu vm, and the IoMmu driver image is present:

dh -p 4e939de9-d948-4b0f-88ed-e6e1ce517c1e -v
Handle dump by protocol '4E939DE9-D948-4B0F-88ED-E6E1CE517C1E'
Shell> dh -p 03c4e603-ac28-11d3-9a2d-0090273fc14d -v
Handle dump by protocol 'PXEBaseCode'
Shell> dh 28 -v
28: 3ECF0C18
ImageDevicePath(3ECF2A98)
 Fv(7CB8BDC9-F8EB-4F34-AAEA-3EE4AF6516A1)/FvFile(8657015B-EA43-440D-949A-AF3BE365C0FC)
LoadedImage(3ECF20C0)
 Name..........: IoMmuDxe

So I am assuming the driver is failing to find hardware. I have tried a few different things, different EDK2 builds and followed the virtio instructions here, but nothing has worked. Ik it worked on hardware, so if you have any ideas on how to get qemu setup for IoMmu please let me know.

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