On Thu, Oct 17, 2013 at 06:43:33PM +0100, Stefano Stabellini wrote: > xen_unmap_single calls xen_bus_to_phys, then passes dev_addr to > is_xen_swiotlb_buffer that calls xen_bus_to_phys again.
It does? I see it call mfn_to_local_pfn which calls pfn_to_mfn and get_phys_to_machine (which I presume is going to be a slow operation on ARM). > xen_bus_to_phys is potentially a slow operation that might involve > walking a tree. > We can avoid calling xen_bus_to_phys twice by removing the > is_xen_swiotlb_buffer call and doing the check directly in > xen_unmap_single using the physical address. > > Signed-off-by: Stefano Stabellini <[email protected]> Have you tested this with a PFN that is in a foreign domain? I am bit uncomfortable with this - I recall when developing this that I had hit some odd cases of doing DMA of a page to a guest and it not always working. It was the case of not detecting whether the pfn was foreign or not. Sadly I can't recall the details. I would think that this problem would also be present with ARM? But perhaps all the new changes in the pfn_to_mfn that had lately been done have fixed this? > --- > drivers/xen/swiotlb-xen.c | 4 ++-- > 1 files changed, 2 insertions(+), 2 deletions(-) > > diff --git a/drivers/xen/swiotlb-xen.c b/drivers/xen/swiotlb-xen.c > index 4d50058..6d9ca61 100644 > --- a/drivers/xen/swiotlb-xen.c > +++ b/drivers/xen/swiotlb-xen.c > @@ -426,8 +426,8 @@ static void xen_unmap_single(struct device *hwdev, > dma_addr_t dev_addr, > > xen_dma_unmap_page(hwdev, paddr, size, dir, attrs); > > - /* NOTE: We use dev_addr here, not paddr! */ > - if (is_xen_swiotlb_buffer(dev_addr)) { > + if (paddr >= virt_to_phys(xen_io_tlb_start) && > + paddr < virt_to_phys(xen_io_tlb_end)) { > swiotlb_tbl_unmap_single(hwdev, paddr, size, dir); > return; > } > -- > 1.7.2.5 > -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to [email protected] More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
