On Thu, Jul 16, 2015 at 05:15:41PM +0100, Julien Grall wrote: > Hi Stefano, > > On 16/07/2015 16:33, Stefano Stabellini wrote: > >On Fri, 10 Jul 2015, Konrad Rzeszutek Wilk wrote: > >>On Thu, Jul 09, 2015 at 09:42:21PM +0100, Julien Grall wrote: > >>>When Linux is using 64K page granularity, every page will be slipt in > >>>multiple non-contiguous 4K MFN (page granularity of Xen). > >> > >>But you don't care about that on the Linux layer I think? > >> > >>As in, is there an SWIOTLB that does PFN to MFN and vice-versa > >>translation? > >> > >>I thought that ARM guests are not exposed to the MFN<->PFN logic > >>and trying to figure that out to not screw up the DMA engine > >>on a PCIe device slurping up contingous MFNs which don't map > >>to contingous PFNs? > > > >Dom0 is mapped 1:1, so pfn == mfn normally, however grant maps > >unavoidably screw up the 1:1, so the swiotlb jumps in to save the day > >when a foreign granted page is involved in a dma operation. > > > >Regarding xen_biovec_phys_mergeable, we could check that all the pfn == > >mfn and return true in that case. > > I mentioned it in the commit message. Although, we would have to loop on > every pfn which is slow on 64KB (16 times for every page). Given the biovec > is called often, I don't think we can do a such things.
OK - it would be good to have the gist of this email thread in the commit message. Thanks. > > Regards, > > -- > Julien Grall -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majord...@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
