From mboxrd@z Thu Jan 1 00:00:00 1970 From: Alok Kataria Subject: Re: swiotlb detection should be memory hotplug aware ? Date: Mon, 15 Mar 2010 10:22:49 -0700 Message-ID: <1268673769.28506.1.camel@ank32> References: <1268446032.13691.69.camel@ank32> <4B9B01F5.3000807@linux.intel.com> Reply-To: akataria@vmware.com Mime-Version: 1.0 Content-Type: text/plain Content-Transfer-Encoding: 7bit Return-path: Received: from smtp-outbound-2.vmware.com ([65.115.85.73]:56659 "EHLO smtp-outbound-2.vmware.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S965538Ab0CORWt (ORCPT ); Mon, 15 Mar 2010 13:22:49 -0400 In-Reply-To: <4B9B01F5.3000807@linux.intel.com> Sender: linux-acpi-owner@vger.kernel.org List-Id: linux-acpi@vger.kernel.org To: Andi Kleen Cc: Len Brown , the arch/x86 maintainers , linux-acpi , LKML , Petr Vandrovec Hi Andi, On Fri, 2010-03-12 at 19:09 -0800, Andi Kleen wrote: > , Alok Kataria wrote: > > Hi Alok, > > > Hi, > > > > Looking at the current code swiotlb is initialized for 64bit kernels > > only when the max_pfn value is greater than 4G (MAX_DMA32_PFN value). > > So in cases when the initial memory is less than 4GB the kernel boots > > without enabling swiotlb, when we hotadd memory to such a kernel and go > > beyond the 4G limit, swiotlb is still disabled. As a result when any > > 32bit devices start using this newly added memory beyond 4G, the kernel > > starts spitting error messages like below or in some cases it causes > > kernel panics. > > Yes seems like a real problem. > > > > > 1. Enable swiotlb for all 64bit kernels which have memory hot-add > > support. > > I don't think that's a good idea. It would enable it everywhere on > distributions which compile with hotadd. Need (2) > > > 2. Instead of checking the max_pfn value in pci_swiotlb_detect, check > > for max_hotpluggable_pfn (or some such) value. Though I don't see such a > > value readily available. I could parse the SRAT and get hotplug memory > > information but that will make swiotlb detection logic a little too > > complex. A quick look around srat_xx.c files and the acpi_memhotplug > > module didn't find any useful API that could be used directly either. > > So was wondering if any of you are aware of an easy way to get such > > information ? > > I have a patchkit to revamp the SRAT parsing to store the hotadd information > more efficiently (the current way is pretty dumb) I need to repost that. Can you please send me any pointers to that patch series. Also am just curious to know about any merge plans for that patchkit. Thanks, Alok > > With that it would be relatively easy to do I think. > > -Andi