ARM64 BBML3 Feature Ready with Linux 7.3, Nvidia Olympus Workarounds

The ARM64 architecture will introduce the BBML3 feature with Linux 7.3, replacing the existing BBML2-noabort code for more efficient page table transitions and improved memory management. The kernel also includes workarounds for broken device memory ordering on NVIDIA's Olympus CPU cores powering Vera, inserting a DMB OSH before each raw MMIO load on affected CPUs. Additionally, in-kernel Branch Target Identification (BTI) is disabled for recent LLVM Clang versions due to livepatching issues, and perf workarounds address hardware issues on AWS Graviton5 and NVIDIA Olympus, with new DDR PMU support for Marvell CN20K SoCs.

ARM64 BBML3 Feature Ready With Linux 7.3, NVIDIA Olympus Workarounds AI/LLM patch craziness hurt ARM64 development https://www.phoronix.com/news/ARM64-Linux-7.2-Changes for the Linux 7.2 cycle that no real features landed for that kernel version on AArch64. Fortunately, the ARM Linux developers are more prepared now and for Linux 7.3 are introducing some new ARM64 features. One of the new features ready to go for ARM64 with Linux 7.3 is the BBML3 feature. Break-Before-Make Level 3 BBML3 is a newer feature of AArch64 for more efficient handling of page table transitions. BBML3 can lead to better optimized memory management and more efficient handling by VM hypervisors. BBML3 is replacing the Linux kernel's existing BBML2-noabort feature code. ARM64 with Linux 7.3 also works around broken device memory ordering with NVIDIA's Olympus CPU cores that power Vera. This bug can leave a peripheral in an incorrect state in breaking program-order guarantees. The workaround is inserting a DMB OSH immediately before each raw MMIO load on affected CPUs. The ARM64 code also ends up disabling in-kernel Branch Target Identification BTI for recent versions of the LLVM Clang compiler due to issues with kernel livepatching that are still being investigated. On the ARM64 perf side there are workarounds for hardware issues on AWS Graviton5 and NVIDIA Olympus. Plus support for the DDR PMU on Marvell CN20K SoCs and other new hardware support. There are also ARM64 bug fixes and other changes as outlined in this pull request https://lore.kernel.org/lkml/aoGIWuq7XL2jnG7s@willie-the-truck/ for the Linux 7.3 merge window.