On a Xen PV guest the DMA addresses and physical addresses are not 1:1 (such as Xen PV guests) and the generic dma_get_required_mask() does not return the correct mask (since it uses max_pfn).
Some device drivers (such as mptsas, mpt2sas) use dma_get_required_mask() to set the device's DMA mask to allow them to use only 32-bit DMA addresses in hardware structures. This results in unnecessary use of the SWIOTLB if DMA addresses are more than 32-bits, impacting performance significantly. We could base the DMA mask on the maximum MFN but: a) The hypercall op to get the maximum MFN (XENMEM_maximum_ram_page) will truncate the result to an int in 32-bit guests. b) Future uses of the IOMMU in Xen may map frames at bus addresses above the end of RAM. So, just assume a 64-bit DMA mask is always required. Signed-off-by: David Vrabel <[email protected]> --- arch/x86/xen/pci-swiotlb-xen.c | 6 ++++++ 1 file changed, 6 insertions(+) diff --git a/arch/x86/xen/pci-swiotlb-xen.c b/arch/x86/xen/pci-swiotlb-xen.c index 0e98e5d..35774f8 100644 --- a/arch/x86/xen/pci-swiotlb-xen.c +++ b/arch/x86/xen/pci-swiotlb-xen.c @@ -18,6 +18,11 @@ int xen_swiotlb __read_mostly; +static u64 xen_swiotlb_get_required_mask(struct device *dev) +{ + return DMA_BIT_MASK(64); +} + static struct dma_map_ops xen_swiotlb_dma_ops = { .mapping_error = xen_swiotlb_dma_mapping_error, .alloc = xen_swiotlb_alloc_coherent, @@ -31,6 +36,7 @@ static struct dma_map_ops xen_swiotlb_dma_ops = { .map_page = xen_swiotlb_map_page, .unmap_page = xen_swiotlb_unmap_page, .dma_supported = xen_swiotlb_dma_supported, + .get_required_mask = xen_swiotlb_get_required_mask, }; /* -- 1.7.10.4 -- 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/
