Re: [PATCH v2 0/2] IOMMU Performance Optimization support

[Boqun Feng <boqun@kernel.org>]

On Mon, Sep 07, 2026 at 11:12:05PM -0500, Mario Limonciello wrote:
> Add support for the AMD IOMMU Performance Optimization (PerfOpt)
> feature as defined in the AMD I/O Virtualization Technology (IOMMU)
> Specification, Section 3.4.9 (MMIO Offset 016Ch).
> 
> This feature allows privileged integrated I/O devices (GPUs) to bypass
> the IOMMU when directly accessing system memory.  The IOMMU only
> enforces the IR/IW permission bits without GPA->SPA translations.
> 
> Drivers will opt into this behavior, and enable amdgpu to turn this
> feature on when an integrated GPU is already in identity mode.
> If a user prefers to keep it always off (even with identity mode)
> there is also a module parameter to force it off.
> 

Our GPU memory accessing benchmark confirms the improvement: without the
patchset, GTT is 2x - 3x slower than VRAM, after this, the latency gap
is almost gone (within 10%). Nice work!

Tested-by: Boqun Feng (Netflix) <boqun@kernel.org>

Regards,
Boqun

> v2:
>  * Rebase on 7.3-rc2
>  * Adjust amdgpu parameter behavior
> 
> Mario Limonciello (2):
>   iommu/amd: Add PerfOpt IOMMU performance optimization support
>   drm/amdgpu: Enable PerfOpt IOMMU perf optimization when GPU in
>     identity domain
> 
>  drivers/gpu/drm/amd/amdgpu/amdgpu.h        |   1 +
>  drivers/gpu/drm/amd/amdgpu/amdgpu_device.c |  50 +++++
>  drivers/gpu/drm/amd/amdgpu/amdgpu_drv.c    |  12 ++
>  drivers/iommu/amd/amd_iommu.h              |   3 +
>  drivers/iommu/amd/amd_iommu_types.h        |   7 +
>  drivers/iommu/amd/init.c                   |  43 +++++
>  drivers/iommu/amd/iommu.c                  | 214 +++++++++++++++++++++
>  include/linux/amd-iommu.h                  |  11 ++
>  8 files changed, 341 insertions(+)
> 
> -- 
> 2.43.0
>