This bug is awaiting verification that the linux-bluefield/6.8.0-1012.16 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-noble-linux-bluefield' to 'verification-done- noble-linux-bluefield'. If the problem still exists, change the tag 'verification-needed-noble-linux-bluefield' to 'verification-failed- noble-linux-bluefield'.
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-noble-linux-bluefield-v2 verification-needed-noble-linux-bluefield -- You received this bug notification because you are a member of Kernel Packages, which is subscribed to linux in Ubuntu. https://bugs.launchpad.net/bugs/2120209 Title: x86 systems with PCIe BAR addresses located outside a certain range see P2PDMA allocation failures and CUDA initialization errors Status in linux package in Ubuntu: Invalid Status in linux source package in Jammy: Won't Fix Status in linux source package in Noble: Fix Committed Status in linux source package in Plucky: Fix Released Bug description: SRU Justification [Impact] On some x86 systems, it is possible for PCIe device BAR addresses to exceed the range reserved by KASLR for direct mappings. This causes attempts to map the impacted BAR region using devm_memremap_pages() to fail. These memmap-backed mappings are required for multiple use-cases, including P2PDMA, and CUDA with Heterogeneous Memory Management (HMM) enabled. [Fix] This is resolved upstream by commit 7ffb791423c7 ("x86/kaslr: Reduce KASLR entropy on most x86 systems"). It changes the behavior of KASLR to not shrink direct mapping space when CONFIG_PCI_P2PDMA is enabled. The consequence of this is that there is less room for KASLR to maneuver, and thus the amount of entropy in the randomized layout is reduced. In discussion on the upstream patch submission [1], it is noted that on the submitter's system this reduces entropy from 16 bits down to 15 bits. Cherry-picking the mentioned commit allows CUDA with HMM enabled and P2PDMA to function on the systems described above, as with it the direct mapping space is not shrunk, so all BAR regions fall within its bounds, and thus the devm_memremap_pages() operation succeeds. Additionally, the commit 7170130e4c72 ("x86/mm/init: Handle the special case of device private pages in add_pages(), to not increase max_pfn and trigger dma_addr essing_limited() bounce buffers") addresses a performance regression revealed by applying commit 7ffb791423c7 ("x86/kaslr: Reduce KASLR entropy on most x86 systems"). Jammy 5.15 has CONFIG_PCI_P2PDMA set to n, so a cherry-pick alone will not resolve the issue. Additionally, Jammy is missing a dependency of 7170130e4c72: e3246d8f5217 ("mm/sparse-vmemmap: add a pgmap argument to section activation"), which has its own set of dependencies. As there does not appear to be significant demand for this in Jammy, and risk of regression is higher, a fix for Jammy is omitted for this submission. Jammy: 7ffb791423c7 already in-tree. Cherry-pick of 7170130e4c72, e3246d8f5217, and CONFIG_PCI_P2PDMA=y needed. Skipped for this submission for regression risk noted above. Noble: Cherry-pick of both commits mentioned above needed. Plucky: Not affected, fix commits already in tree and CONFIG_PCI_P2PDMA=y. Questing: Not affected, fix commits already in tree and config set and CONFIG_PCI_P2PDMA=y. [Test Case] The issue only occurs on systems with PCIe BAR addresses located outside of the current minimum address range of [0, ceil(max_pfn / 1TiB) + CONFIG_RANDOMIZE_MEMORY_PHYSICAL_PADDING (10 TiB)]. With the NVIDIA Container Toolkit installed and enabled for Docker, the following reproduces the issue on affected systems where one or more NVIDIA GPUs have BAR addresses outside of the current minimum range: $ sudo docker run --runtime nvidia --rm -it nvcr.io/nvidia/pytorch:25.03-py3 ERROR: The NVIDIA Driver is present, but CUDA failed to initialize. GPU functionality will not be available. [[ Initialization error (error 3) ]] [Where things could go wrong] This reduces the entropy of the memory layouts KASLR generates on most x86 systems. A bug would likely show up as misbehavior of KASLR. [Other Notes] [1] https://lore.kernel.org/lkml/202502061145.8AFAF053E4@keescook/ [2] https://bugs.launchpad.net/bugs/1987394 v2: drop patches for Jammy due to greater regression risk as noted in Fix section. Balbir Singh (2): x86/kaslr: Reduce KASLR entropy on most x86 systems x86/mm/init: Handle the special case of device private pages in add_pages(), to not increase max_pfn and trigger dma_addressing_limited() bounce buffers arch/x86/mm/init_64.c | 15 ++++++++++++--- arch/x86/mm/kaslr.c | 10 ++++++++-- drivers/pci/Kconfig | 6 ++++++ 3 files changed, 26 insertions(+), 5 deletions(-) -- 2.43.0 To manage notifications about this bug go to: https://bugs.launchpad.net/ubuntu/+source/linux/+bug/2120209/+subscriptions -- Mailing list: https://launchpad.net/~kernel-packages Post to : [email protected] Unsubscribe : https://launchpad.net/~kernel-packages More help : https://help.launchpad.net/ListHelp
