After ChkTag [1] announcement, it's worth preparing a stable x86 linear address masking (lam) user interface. One important aspect of lam is the tag width, and aligning it with other industry solutions can provide a more popular, generalized interface that other technologies could utilize.
ChkTag will use 4-bit tags and since that's the direction other memory tagging implementations seem to be taking too (for example Arm's MTE) it's reasonable to converge lam in linux to the same specification. Even though x86's LAM supports 6-bit tags it is beneficial to default lam to 4 bits as ChkTag will likely be the main user of the interface and such connection should simplify things in the future. 6-bit tags should still be available as a debug feature and possible to enable through debugfs. Tag width can be system wide whether it's the default 4 bits or debug 6 bits and when a process requests a specific tag width it should get the max amount enabled globally. Series also cleans up some comments referencing LAM_U48 which was not implemented in the kernel and the comments shouldn't imply it can be enabled. Patches are based on v6.19. [1] https://community.intel.com/t5/Blogs/Tech-Innovation/open-intel/ChkTag-x86-Memory-Safety/post/1721490 Maciej Wieczor-Retman (4): x86/process: Shorten the default LAM tag width x86/process: Add a debug interface to change LAM tag width x86/mm: Cleanup comments where LAM_U48 is mentioned selftests/lam: Add test cases for different LAM tag widths arch/x86/include/asm/mmu.h | 2 +- arch/x86/include/asm/mmu_context.h | 3 ++ arch/x86/include/asm/tlbflush.h | 2 +- arch/x86/kernel/process_64.c | 71 +++++++++++++++++++++--- tools/testing/selftests/x86/lam.c | 87 +++++++++++++++++++++++++----- 5 files changed, 144 insertions(+), 21 deletions(-) -- 2.53.0
