From b6ccb9803e90c16b212cf4ed62913a7591e79a39 Mon Sep 17 00:00:00 2001 From: Will Deacon Date: Fri, 7 Feb 2014 19:12:27 +0100 Subject: ARM: 7954/1: mm: remove remaining domain support from ARMv6 CPU_32v6 currently selects CPU_USE_DOMAINS if CPU_V6 and MMU. This is because ARM 1136 r0pX CPUs lack the v6k extensions, and therefore do not have hardware thread registers. The lack of these registers requires the kernel to update the vectors page at each context switch in order to write a new TLS pointer. This write must be done via the userspace mapping, since aliasing caches can lead to expensive flushing when using kmap. Finally, this requires the vectors page to be mapped r/w for kernel and r/o for user, which has implications for things like put_user which must trigger CoW appropriately when targetting user pages. The upshot of all this is that a v6/v7 kernel makes use of domains to segregate kernel and user memory accesses. This has the nasty side-effect of making device mappings executable, which has been observed to cause subtle bugs on recent cores (e.g. Cortex-A15 performing a speculative instruction fetch from the GIC and acking an interrupt in the process). This patch solves this problem by removing the remaining domain support from ARMv6. A new memory type is added specifically for the vectors page which allows that page (and only that page) to be mapped as user r/o, kernel r/w. All other user r/o pages are mapped also as kernel r/o. Patch co-developed with Russell King. Cc: Signed-off-by: Will Deacon Signed-off-by: Russell King --- arch/arm/mm/Kconfig | 3 +-- 1 file changed, 1 insertion(+), 2 deletions(-) (limited to 'arch/arm/mm/Kconfig') diff --git a/arch/arm/mm/Kconfig b/arch/arm/mm/Kconfig index 1f8fed94c2a4..ca8ecdee47d8 100644 --- a/arch/arm/mm/Kconfig +++ b/arch/arm/mm/Kconfig @@ -446,7 +446,6 @@ config CPU_32v5 config CPU_32v6 bool - select CPU_USE_DOMAINS if CPU_V6 && MMU select TLS_REG_EMUL if !CPU_32v6K && !MMU config CPU_32v6K @@ -671,7 +670,7 @@ config ARM_VIRT_EXT config SWP_EMULATE bool "Emulate SWP/SWPB instructions" - depends on !CPU_USE_DOMAINS && CPU_V7 + depends on CPU_V7 default y if SMP select HAVE_PROC_CPU if PROC_FS help -- cgit