(2013/09/09 18:07), David Woodhouse wrote: > On Wed, 2013-08-21 at 16:15 +0900, Takao Indoh wrote: >> >> This causes problem on kdump. Devices are working in first kernel, and >> after switching to second kernel and initializing IOMMU, many DMAR faults >> occur and it causes problems like driver error or PCI SERR, at last >> kdump fails. This patch fixes this problem. > > I'm not sure I'd call this a fix. > > If the driver is so broken that it cannot get the device working again > after a fault, surely the driver needs to be fixed? Yes,this problem may be solved by fixing driver. Actually megaraid sas driver is recently fixed for this problem. (See commit 6431f5d7) But I think root cause of this problem is initializing IOMMU while DMA is still working, and I want to solve the root cause rather than handling it in each driver, otherwise we have to fix driver each time we find this kind of problem. > > If the system is suffering an IRQ storm because device doesn't give up > after the first few faults, then we should switch off the fault > *reporting* for that device so that its faults get ignored (until it > next actually sets up a DMA mapping, or something). In such a case, yeah limiting messages is enough. > > For the IOMMU code to reset individual devices, just because they still > have an active DMA mapping even if they're not *doing* DMA, seems wrong. > You'll even end up resetting devices just because they have an RMRR, > won't you? (Although I wouldn't lose any sleep over that, I suppose. In > fact it might be a *feature*... :) Right, current code is resetting devices which *may* be doing DMA. The ideal way is finding devices which are actually doing DMA and reset only them but I don't know how we can do this, though I think current code is sufficient. Thanks, Takao Indoh
