First of all, sorry for the horribly big Cc list! Following up to the discussion in: https://lore.kernel.org/r/20200914204209.256266093@xxxxxxxxxxxxx this provides a preemptible variant of kmap_atomic & related interfaces. This is achieved by: - Consolidating all kmap atomic implementations in generic code - Switching from per CPU storage of the kmap index to a per task storage - Adding a pteval array to the per task storage which contains the ptevals of the currently active temporary kmaps - Adding context switch code which checks whether the outgoing or the incoming task has active temporary kmaps. If so, the outgoing task's kmaps are removed and the incoming task's kmaps are restored. - Adding new interfaces k[un]map_temporary*() which are not disabling preemption and can be called from any context (except NMI). Contrary to kmap() which provides preemptible and "persistant" mappings, these interfaces are meant to replace the temporary mappings provided by kmap_atomic*() today. This allows to get rid of conditional mapping choices and allows to have preemptible short term mappings on 64bit which are today enforced to be non-preemptible due to the highmem constraints. It clearly puts overhead on the highmem users, but highmem is slow anyway. This is not a wholesale conversion which makes kmap_atomic magically preemptible because there might be usage sites which rely on the implicit preempt disable. So this needs to be done on a case by case basis and the call sites converted to kmap_temporary. Note, that this is only lightly tested on X86 and completely untested on all other architectures. The lot is also available from git://git.kernel.org/pub/scm/linux/kernel/git/tglx/devel.git highmem Thanks, tglx --- a/arch/arm/mm/highmem.c | 121 --------------------- a/arch/microblaze/mm/highmem.c | 78 ------------- a/arch/nds32/mm/highmem.c | 48 -------- a/arch/powerpc/mm/highmem.c | 67 ----------- a/arch/sparc/mm/highmem.c | 115 -------------------- arch/arc/Kconfig | 1 arch/arc/include/asm/highmem.h | 8 + arch/arc/mm/highmem.c | 44 ------- arch/arm/Kconfig | 1 arch/arm/include/asm/highmem.h | 30 +++-- arch/arm/mm/Makefile | 1 arch/csky/Kconfig | 1 arch/csky/include/asm/highmem.h | 4 arch/csky/mm/highmem.c | 75 ------------- arch/microblaze/Kconfig | 1 arch/microblaze/include/asm/highmem.h | 6 - arch/microblaze/mm/Makefile | 1 arch/microblaze/mm/init.c | 6 - arch/mips/Kconfig | 1 arch/mips/include/asm/highmem.h | 4 arch/mips/mm/highmem.c | 77 ------------- arch/mips/mm/init.c | 3 arch/nds32/Kconfig.cpu | 1 arch/nds32/include/asm/highmem.h | 21 ++- arch/nds32/mm/Makefile | 1 arch/powerpc/Kconfig | 1 arch/powerpc/include/asm/highmem.h | 6 - arch/powerpc/mm/Makefile | 1 arch/powerpc/mm/mem.c | 7 - arch/sparc/Kconfig | 1 arch/sparc/include/asm/highmem.h | 7 - arch/sparc/mm/Makefile | 3 arch/sparc/mm/srmmu.c | 2 arch/x86/include/asm/fixmap.h | 1 arch/x86/include/asm/highmem.h | 12 +- arch/x86/include/asm/iomap.h | 29 +++-- arch/x86/mm/highmem_32.c | 59 ---------- arch/x86/mm/init_32.c | 15 -- arch/x86/mm/iomap_32.c | 57 ---------- arch/xtensa/Kconfig | 1 arch/xtensa/include/asm/highmem.h | 9 + arch/xtensa/mm/highmem.c | 44 ------- b/arch/x86/Kconfig | 3 include/linux/highmem.h | 141 +++++++++++++++--------- include/linux/io-mapping.h | 2 include/linux/sched.h | 9 + kernel/sched/core.c | 10 + mm/Kconfig | 3 mm/highmem.c | 192 ++++++++++++++++++++++++++++++++-- 49 files changed, 422 insertions(+), 909 deletions(-)
