On Tue, Mar 16, 2010 at 10:33:20AM +0900, FUJITA Tomonori wrote: > On Mon, 15 Mar 2010 20:51:40 -0400 > Konrad Rzeszutek Wilk <konrad.wilk@xxxxxxxxxx> wrote: > > > On Fri, Mar 12, 2010 at 07:09:41PM -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 > > > > There is a late mechanism to do kickoff the SWIOTLB. Perhaps the hot-add > > could use swiotlb_init_late and start up the SWIOTLB? > > I guess that you are talking about > swiotlb_late_init_with_default_size(), which IA64 uses. However, you > can use swiotlb_late_init_with_default_size() only before we > initialize devices. Making it work after initializing devices is not > so easy, I think (that is, we need to change dma_ops). That is a good point. Especially if we have some outstanding DMA pages allocated via dma_alloc_coherent. I thought that the machines that have hot-add memory they have their own fancy IOMMU. For example the IBM x3955 (and its family) utilize the Calgary IOMMU. The HP boxes utilize the Intel VT-D (or the AMD equivalant). So is this mostly specialized in the areas of virtualized guests? (Xen PV guests with PCI passthrough suffer the same problem, btw). -- To unsubscribe from this list: send the line "unsubscribe linux-acpi" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
