From mboxrd@z Thu Jan 1 00:00:00 1970 From: Andi Kleen Subject: Re: swiotlb detection should be memory hotplug aware ? Date: Fri, 12 Mar 2010 19:09:41 -0800 Message-ID: <4B9B01F5.3000807@linux.intel.com> References: <1268446032.13691.69.camel@ank32> Mime-Version: 1.0 Content-Type: text/plain; charset=ISO-8859-15; format=flowed Content-Transfer-Encoding: 7bit Return-path: Received: from mga07.intel.com ([143.182.124.22]:21365 "EHLO azsmga101.ch.intel.com" rhost-flags-OK-OK-OK-FAIL) by vger.kernel.org with ESMTP id S1757945Ab0CMDJn (ORCPT ); Fri, 12 Mar 2010 22:09:43 -0500 In-Reply-To: <1268446032.13691.69.camel@ank32> Sender: linux-acpi-owner@vger.kernel.org List-Id: linux-acpi@vger.kernel.org To: akataria@vmware.com Cc: Len Brown , the arch/x86 maintainers , linux-acpi , LKML , Petr Vandrovec , 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. With that it would be relatively easy to do I think. -Andi