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  1. Bug #1745118
  2. Comment #14

Comment 14 for bug 1745118

Revision history for this message
William Grant (wgrant) wrote :

I've only been able to reproduce this on systems with an Intel IOMMU. Disabling the IOMMU in the firmware (usually labelled "VT-d") lets the latest 4.13 i386 kernel boot. It's also reproducible in qemu if you give it an IOMMU, eg. "-machine q35 -device intel-iommu".

The problem is that the IDT page (0xffc00000) overlaps the FIX_BTMAPS range. IOMMU detection tries to read ACPI tables, which eventually calls early_ioremap, which maps an ACPI table over the IDT, and then eventually unmaps it completely. The first kernel interrupt after that (usually in test_wp_bit) triple-faults when it can't find the IDT.

I've built an experimental kernel with the FIX_BTMAPS vs IDT conflict fixed at https://people.canonical.com/~wgrant/linux-image-4.13.0-31-generic_4.13.0-31.34~16.04.1_i386.deb. It works on my affected hardware and qemu, but it would be good to confirm that it's the same issue that others have.