Messages in this thread | | | Date | Wed, 14 Aug 2013 14:01:33 +0100 | From | Stefano Stabellini <> | Subject | Re: [PATCH v3 09/10] swiotlb-xen: support autotranslate guests |
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On Fri, 9 Aug 2013, Konrad Rzeszutek Wilk wrote: > > @@ -193,9 +315,10 @@ retry: > > /* > > * Get IO TLB memory from any location. > > */ > > - if (early) > > + if (early) { > > xen_io_tlb_start = alloc_bootmem_pages(PAGE_ALIGN(bytes)); > > - else { > > + xen_dma_seg = alloc_bootmem(sizeof(struct xen_dma_info) * NR_DMA_SEGS); > > So what if the user over-wrote the size of the SWITOLB? Meaning the nslabs is different? > Won't that blow up in xen_swiotlb_fixup if we try to dereference past the array?
The definition of NR_DMA_SEGS is:
#define NR_DMA_SEGS ((xen_io_tlb_nslabs + IO_TLB_SEGSIZE - 1) / IO_TLB_SEGSIZE)
xen_io_tlb_nslabs is calculated from io_tlb_nslabs.
If the user increases io_tlb_nslabs, then xen_io_tlb_nslabs and NR_DMA_SEGS are also going to be bigger.
> > @@ -351,14 +477,15 @@ dma_addr_t xen_swiotlb_map_page(struct device *dev, struct page *page, > > * we can safely return the device addr and not worry about bounce > > * buffering it. > > */ > > - if (dma_capable(dev, dev_addr, size) && > > + if (!xen_feature(XENFEAT_auto_translated_physmap) && > > + dma_capable(dev, dev_addr, size) && > > !range_straddles_page_boundary(phys, size) && !swiotlb_force) > > return dev_addr; > > > > /* > > * Oh well, have to allocate and map a bounce buffer. > > */ > > - map = swiotlb_tbl_map_single(dev, start_dma_addr, phys, size, dir); > > + map = swiotlb_tbl_map_single(dev, xen_dma_seg[0].dma_addr, phys, size, dir); > > That [0] really deserves a comment.
xen_dma_seg[0].dma_addr corresponds exactly to start_dma_addr, the first machine address of the swiotlb buffer. I think that reason why we pass the dma address of the first slab is that we want to allocate the bounce buffer from any of the slabs in io_tlb_start-io_tlb_end.
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