From 9d99c7123c9af5f47a2037933a3ffaec3e37efad Mon Sep 17 00:00:00 2001 From: Christian Melki Date: Mon, 5 Oct 2015 17:31:33 +0200 Subject: [PATCH] swiotlb: Enable it under x86 PAE Most distributions end up enabling SWIOTLB already with 32-bit kernels due to the combination of CONFIG_HYPERVISOR_GUEST|CONFIG_XEN=y as those end up requiring the SWIOTLB. However for those that are not interested in virtualization and run in 32-bit they will discover that: "32-bit PAE 4.2.0 kernel (no IOMMU code) would hang when writing to my USB disk. The kernel spews million(-ish messages per sec) to syslog, effectively "hanging" userspace with my kernel. Oct 2 14:33:06 voodoochild kernel: [ 223.287447] nommu_map_sg: overflow 25dcac000+1024 of device mask ffffffff Oct 2 14:33:06 voodoochild kernel: [ 223.287448] nommu_map_sg: overflow 25dcac000+1024 of device mask ffffffff Oct 2 14:33:06 voodoochild kernel: [ 223.287449] nommu_map_sg: overflow 25dcac000+1024 of device mask ffffffff ... etc ..." Enabling it makes the problem go away. N.B. With a6dfa128ce5c414ab46b1d690f7a1b8decb8526d "config: Enable NEED_DMA_MAP_STATE by default when SWIOTLB is selected" we also have the important part of the SG macros enabled to make this work properly - in case anybody wants to backport this patch. Reported-and-Tested-by: Christian Melki Signed-off-by: Christian Melki Signed-off-by: Konrad Rzeszutek Wilk --- arch/x86/Kconfig | 1 + 1 file changed, 1 insertion(+) diff --git a/arch/x86/Kconfig b/arch/x86/Kconfig index 328c8352480c..96d058a87100 100644 --- a/arch/x86/Kconfig +++ b/arch/x86/Kconfig @@ -1308,6 +1308,7 @@ config HIGHMEM config X86_PAE bool "PAE (Physical Address Extension) Support" depends on X86_32 && !HIGHMEM4G + select SWIOTLB ---help--- PAE is required for NX support, and furthermore enables larger swapspace support for non-overcommit purposes. It -- GitLab