ACK: [SRU][R][PATCH v2 0/1] [SRU][R][PATCH v2 0/1] drm/amdgpu: cap GTT size to physical RAM on APUs

[Edoardo Canepa]

Acked-by: Edoardo Canepa <edoardo.canepa at canonical.com>

On 8/28/26 11:06, Yo-Jung Leo Lin (AMD) via kernel-team wrote:
> BugLink: https://bugs.launchpad.net/bugs/2162038
>
> [ Impact ]
>
> On AMD APU systems, there are few ways to tweak memory being used by the amdgpu driver. Notably:
>
> - VRAM size can be tweaked by: UMA carveout by the BIOS/sysfs interfaces.
> - GTT size can be tweaked by module parameters in the TTM module.
>
> Currently, the mechanisms above works independently. However, on APU systems, because total physical memory is shared among the above and is partitioned into them, the calculation needs to take the total physical memory into account. Otherwise the driver would be double-booking physical memory, leading to issues like [1].
>
> [ Fix ]
>
> Cherry-pick the following commit:
>
> - drm/amdgpu: cap GTT size to physical RAM on APUs[2]
>
> [ Test Plan ]
>
> - Boot into the kernel with a large non-carveout memory space (~512MB out of 64G total memory) and accordingly set a large GTT (~48GB) via the ttm module parameter (ttm.pages_limit=12582912).
> - Lower the non-carveout memory space in BIOS/sysfs by increasing the UMA Frame Buffer Size (VRAM) to 48GB and reboot.
> - The previously set GTT value (~48GB) should be capped to the non-carveout space, showing the following message:
>
>      [    5.096745] amdgpu 0000:c3:00.0:  49152M of VRAM memory ready
>      [    5.096753] amdgpu 0000:c3:00.0: Capping GTT to 14654M to not exceed available system memory
>
> For reference, previously it shows:
>
>      [    4.980841] amdgpu 0000:c3:00.0:  49152M of VRAM memory ready
>      [    4.980843] amdgpu 0000:c3:00.0:  49152M of GTT memory ready.
>
> [ Where the problems could occur ]
>
> Because the old driver is double-counting memory sizes, a user with this update may feel that memory become less, when in fact that memory is double-counted and never exists.
>
> This impacts memory calculation on GTT for APU systems.
>
> [ Additional Information ]
>
> [1] https://github.com/ROCm/ROCm/issues/6004
> [2] https://lore.kernel.org/amd-gfx/20260727194207.176803-1-harkirat.gill@amd.com/
>
> ---
> Alessio Faina raised an issue in the original patch[1] where Christian König NACKed this patch upstream. After talking to our internal people the decision seems to be ignoring that NACK[2] and let the patch in. It's now part of v7.2 kernel[3]. Update the patch provenance and send it again.
>
> [1] https://lists.ubuntu.com/archives/kernel-team/2026-August/171160.html
> [2] https://bugs.launchpad.net/amd/+bug/2161999/comments/5
> [3] https://github.com/torvalds/linux/commit/5e70f6804b4d6256058c360b10e044ee04ea4a4e
> ---
>
> Harkirat Gill (1):
>    drm/amdgpu: cap GTT size to physical RAM on APUs
>
>   drivers/gpu/drm/amd/amdgpu/amdgpu_ttm.c | 12 ++++++++++++
>   1 file changed, 12 insertions(+)
>
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