Messages in this thread Patch in this message | | | From | Christian Melki <> | Subject | SWIOTLB on 32-bit PAE | Date | Mon, 5 Oct 2015 10:31:39 +0200 |
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Hi,
I discovered that my 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 ...
In my kernel config I noticed that SWIOTLB was not on. It seems SWIOTLB is provided for 64-bit and 32-bit with IOMMU/AGPGART code. But if I compiled the kernel with PAE and no IOMMU and no other GART code, I would not get SWIOTLB. I'd like to think that SWIOTLB should be selected for 32-bit PAE as default.
I have attached a oneliner patch which does that. The patch works for me. The issue where the kernel more or less runs endless bashing of (nommu_?)map_sg when failing is another problem I guess. I expected the kernel/drivers to have some more graceful handling, but I know to little about this area to have a proper opinion.
Regards, Christian diff -urN linux-4.2.orig/arch/x86/Kconfig linux-4.2/arch/x86/Kconfig --- linux-4.2.orig/arch/x86/Kconfig 2015-10-05 08:56:58.933313678 +0200 +++ linux-4.2/arch/x86/Kconfig 2015-10-05 09:00:00.916306025 +0200 @@ -1282,6 +1282,7 @@ 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 | |