Merge branch 'work.splice_read' of git://git.kernel.org/pub/scm/linux/kernel/git...

[cascardo/linux.git] / arch / Kconfig

diff --git a/arch/Kconfig b/arch/Kconfig
index fd6e971..180ea33 100644 (file)
--- a/arch/Kconfig
+++ b/arch/Kconfig
@@ -696,4 +696,38 @@ config ARCH_NO_COHERENT_DMA_MMAP
 config CPU_NO_EFFICIENT_FFS
        def_bool n
 
+config HAVE_ARCH_VMAP_STACK
+       def_bool n
+       help
+         An arch should select this symbol if it can support kernel stacks
+         in vmalloc space.  This means:
+
+         - vmalloc space must be large enough to hold many kernel stacks.
+           This may rule out many 32-bit architectures.
+
+         - Stacks in vmalloc space need to work reliably.  For example, if
+           vmap page tables are created on demand, either this mechanism
+           needs to work while the stack points to a virtual address with
+           unpopulated page tables or arch code (switch_to() and switch_mm(),
+           most likely) needs to ensure that the stack's page table entries
+           are populated before running on a possibly unpopulated stack.
+
+         - If the stack overflows into a guard page, something reasonable
+           should happen.  The definition of "reasonable" is flexible, but
+           instantly rebooting without logging anything would be unfriendly.
+
+config VMAP_STACK
+       default y
+       bool "Use a virtually-mapped stack"
+       depends on HAVE_ARCH_VMAP_STACK && !KASAN
+       ---help---
+         Enable this if you want the use virtually-mapped kernel stacks
+         with guard pages.  This causes kernel stack overflows to be
+         caught immediately rather than causing difficult-to-diagnose
+         corruption.
+
+         This is presently incompatible with KASAN because KASAN expects
+         the stack to map directly to the KASAN shadow map using a formula
+         that is incorrect if the stack is in vmalloc space.
+
 source "kernel/gcov/Kconfig"