[PATCH v8 18/19] swiotlb-xen: no need to do execute two bus_to_phys translations in a row
From: Konrad Rzeszutek Wilk <hidden>
Date: 2013-10-23 14:03:25
Also in:
lkml, xen-devel
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 <redacted>
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?
quoted hunk ↗ jump to hunk
--- 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