On Wed, 2013-04-03 at 16:11 +0900, Takao Indoh wrote: > (2013/04/02 23:05), Joerg Roedel wrote: > > On Mon, Apr 01, 2013 at 02:45:18PM +0900, Takao Indoh wrote: > >> <Current flow on kdump boot> > >> enable_IR > >> intel_enable_irq_remapping > >> iommu_disable_irq_remapping <== IRES/QIES/TES disabled here > >> dmar_disable_qi <== do nothing > >> dmar_enable_qi <== QIES enabled > >> intel_setup_irq_remapping <== IRES enabled > > > > But what we want to do here in the kdumo case is to disable translation > > too, right? Because the former kernel might have translation and > > irq-remapping enabled and the kdump kernel might be compiled without > > support for dma-remapping. So if we don't disable translation here too > > the kdump kernel is unable to do DMA. > > Yeah, you are right. I forgot such a case. If you disable translation and there's some device still doing DMA, it's going to scribble over random areas of memory. You really want to have translation enabled and all the page tables *cleared*, during kexec. I think it's fair to insist that the secondary kernel should use the IOMMU if the first one did. > To be honest, I also expected the side effect of this patch. As I wrote > in the previous mail, I'm working on kdump problem with iommu, that is, > ongoing DMA causes DMAR fault in 2nd kernel and sometimes kdump fails > due to this fault. Here you've lost me. The DMAR fault is caught and reported, and how does this lead to a kdump failure? Are you using dodgy hardware that just keeps *trying* after an abort, and floods the system with a storm of DMAR faults? We've occasionally spoken about working around such a problem by setting a bit to make subsequent faults *silent*. Would that work? > What we have to do is stopping DMA transaction > before DMA-remapping is disabled in 2nd kernel. The IOMMU is there to stop DMA transactions. That is its *job*. :) -- David Woodhouse Open Source Technology Centre David.Woodhouse at intel.com Intel Corporation -------------- next part -------------- A non-text attachment was scrubbed... Name: smime.p7s Type: application/x-pkcs7-signature Size: 6171 bytes Desc: not available URL: <http://lists.infradead.org/pipermail/kexec/attachments/20130403/a3d5416c/attachment.bin>
