From 825c43f50e3aa811a291ffcb40e02fbf6d91ba86 Mon Sep 17 00:00:00 2001 From: Ard Biesheuvel Date: Fri, 19 Nov 2021 16:43:55 -0800 Subject: kmap_local: don't assume kmap PTEs are linear arrays in memory The kmap_local conversion broke the ARM architecture, because the new code assumes that all PTEs used for creating kmaps form a linear array in memory, and uses array indexing to look up the kmap PTE belonging to a certain kmap index. On ARM, this cannot work, not only because the PTE pages may be non-adjacent in memory, but also because ARM/!LPAE interleaves hardware entries and extended entries (carrying software-only bits) in a way that is not compatible with array indexing. Fortunately, this only seems to affect configurations with more than 8 CPUs, due to the way the per-CPU kmap slots are organized in memory. Work around this by permitting an architecture to set a Kconfig symbol that signifies that the kmap PTEs do not form a lineary array in memory, and so the only way to locate the appropriate one is to walk the page tables. Link: https://lore.kernel.org/linux-arm-kernel/20211026131249.3731275-1-ardb@kernel.org/ Link: https://lkml.kernel.org/r/20211116094737.7391-1-ardb@kernel.org Fixes: 2a15ba82fa6c ("ARM: highmem: Switch to generic kmap atomic") Signed-off-by: Ard Biesheuvel Reported-by: Quanyang Wang Reviewed-by: Linus Walleij Acked-by: Russell King (Oracle) Cc: Thomas Gleixner Cc: Signed-off-by: Andrew Morton Signed-off-by: Linus Torvalds --- arch/arm/Kconfig | 1 + 1 file changed, 1 insertion(+) (limited to 'arch/arm') diff --git a/arch/arm/Kconfig b/arch/arm/Kconfig index f0f9e8bec83a..c2724d986fa0 100644 --- a/arch/arm/Kconfig +++ b/arch/arm/Kconfig @@ -1463,6 +1463,7 @@ config HIGHMEM bool "High Memory Support" depends on MMU select KMAP_LOCAL + select KMAP_LOCAL_NON_LINEAR_PTE_ARRAY help The address space of ARM processors is only 4 Gigabytes large and it has to accommodate user address space, kernel address -- cgit v1.2.3