On Mon, Jan 12, 2015 at 03:06:20PM +0800, Li, Zhen-Hua wrote: > + > +#ifdef CONFIG_CRASH_DUMP > + > +/* > + * Fix Crashdump failure caused by leftover DMA through a hardware IOMMU > + * > + * Fixes the crashdump kernel to deal with an active iommu and legacy > + * DMA from the (old) panicked kernel in a manner similar to how legacy > + * DMA is handled when no hardware iommu was in use by the old kernel -- > + * allow the legacy DMA to continue into its current buffers. > + * > + * In the crashdump kernel, this code: > + * 1. skips disabling the IOMMU's translating of IO Virtual Addresses (IOVA). > + * 2. Do not re-enable IOMMU's translating. > + * 3. In kdump kernel, use the old root entry table. > + * 4. Leaves the current translations in-place so that legacy DMA will > + * continue to use its current buffers. > + * 5. Allocates to the device drivers in the crashdump kernel > + * portions of the iova address ranges that are different > + * from the iova address ranges that were being used by the old kernel > + * at the time of the panic. > + * > + */ It looks like you are still copying the io-page-tables from the old kernel into the kdump kernel, is that right? With the approach that was proposed you only need to copy over the context entries 1-1. They are still pointing to the page-tables in the old kernels memory (which is just fine). The root-entry of the old kernel is also re-used, and when the kdump kernel starts to use a device, its context entry is updated to point to a newly allocated page-table. Joerg
