On Fri, 7 Nov 2014, Stefano Stabellini wrote: > On Fri, 7 Nov 2014, Catalin Marinas wrote: > > What I would like to see is xen_dma_map_page() also using hyp calls for > > cache maintenance when !pfn_valid(), for symmetry with unmap. You would > > need another argument to xen_dma_map_page() though to pass the real > > device address or mfn (and on the map side you could simply check for > > page_to_pfn(page) != mfn). For such cases, Xen swiotlb already handles > > bouncing so you don't need dom0 swiotlb involved as well. > > I can see that it would be nice to have map_page and unmap_page be > symmetrical. However actually doing the map_page flush with an hypercall > would slow things down. Hypercalls are slower than function calls. It is > faster to do the cache flushing in dom0 if possible. In the map_page > case we have the struct page so we can easily do it by calling the > native dma_ops function. > > Maybe I could just add a comment to explain the reason for the asymmetry?
Ah, but the problem is that map_page could allocate a swiotlb buffer (actually it does on arm64) that without a corresponding unmap_page call, would end up being leaked, right? Oh well.. two hypercalls it is then :-/ -- 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/
