[Bug 2162038] Re: [SRU] Fix incorrect GTT calculation on the APU systems

This bug is awaiting verification that the linux-oem-7.0/7.0.0-1014.14 kernel in -proposed solves the problem. Please test the kernel and update this bug with the results. If the problem is solved, change the tag 'verification-needed-resolute-linux-oem-7.0' to 'verification-done- resolute-linux-oem-7.0'. If the problem still exists, change the tag 'verification-needed-resolute-linux-oem-7.0' to 'verification-failed- resolute-linux-oem-7.0'. If verification is not done by 5 working days from today, this fix will be dropped from the source code, and this bug will be closed. See https://wiki.ubuntu.com/Testing/EnableProposed for documentation how to enable and use -proposed. Thank you! ** Tags added: kernel-spammed-resolute-linux-oem-7.0-v2 verification-needed-resolute-linux-oem-7.0 -- You received this bug notification because you are subscribed to linux in Ubuntu. Matching subscriptions: Bgg, Bmail, Nb https://bugs.launchpad.net/bugs/2162038 Title: [SRU] Fix incorrect GTT calculation on the APU systems Status in linux package in Ubuntu: New Status in linux-oem-7.0 package in Ubuntu: New Status in linux source package in Resolute: New Status in linux-oem-7.0 source package in Resolute: Fix Committed Bug description: 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/ To manage notifications about this bug go to: https://bugs.launchpad.net/ubuntu/+source/linux/+bug/2162038/+subscriptions