On Tue, 2010-03-16 at 05:45 -0700, Konrad Rzeszutek Wilk wrote: > 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 > > > Andi...ping any pointers to the patchkit. > > > 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 don't see why we need to do this via late_init, swiotlb detection that happens through pci_swiotlb_detect, is already late enough that SRAT is already parsed. Or am I missing something ? > > > > 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). I am assuming that there were Intel based servers which supported memory hot-add before VT-d too. So, IMO this is not specialized to virtualization, though might be hard to prove if there are actual physical machines out there which have similar constraints (no HWIOMMU + MEMHOT add support) Thanks, Alok -- 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
