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Igor Druzhinin
12c36f577d
It's unsafe to disable IOMMU on a live system which is the case if we're crashing since remapping hardware doesn't usually know what to do with ongoing bus transactions and frequently raises NMI/MCE/SMI, etc. (depends on the firmware configuration) to signal these abnormalities. This, in turn, doesn't play well with kexec transition process as there is no handling available at the moment for this kind of events resulting in failures to enter the kernel. Modern Linux kernels taught to copy all the necessary DMAR/IR tables following kexec from the previous kernel (Xen in our case) - so it's currently normal to keep IOMMU enabled. It might require minor changes to kdump command line that enables IOMMU drivers (e.g. intel_iommu=on / intremap=on) but recent kernels don't require any additional changes for the transition to be transparent. A fallback option is still left for compatibility with ancient crash kernels which didn't like to have IOMMU active under their feet on boot. Signed-off-by: Igor Druzhinin <igor.druzhinin@citrix.com> Acked-by: Jan Beulich <jbeulich@suse.com>