On Tue, Nov 05, 2013 at 05:03:58PM +0100, Roger Pau Monné wrote: > On 05/11/13 16:08, Ian Campbell wrote: > > On Tue, 2013-11-05 at 16:01 +0100, Roger Pau Monné wrote: > >> On 05/11/13 15:56, Konrad Rzeszutek Wilk wrote: > >>> On Tue, Nov 05, 2013 at 03:47:08PM +0100, Roger Pau Monné wrote: > >>>> On 05/11/13 13:36, David Vrabel wrote: > >>>>> On 05/11/13 11:24, Roger Pau Monne wrote: > >>>>>> IMHO there's no reason to set a m2p override if the mapping is done in > >>>>>> kernel space, so only set the m2p override when kmap_ops is set. > >>>>> > >>>>> Can you provide a more detailed reasoning about why this is safe? > >>>> > >>>> To tell the truth, I don't understand why we need to use the m2p > >>>> override for kernel space only mappings, my understanding is that this > >>>> m2p override is needed for user space mappings only (where we actually > >>>> end up doing two mappings, one in kernel space and one in user space). > >>>> For kernel space I don't see why we need to do anything else than > >>>> setting the right p2m translation. > >>> > >>> We needed the m2p when doing DMA operations. As the driver would > >>> want the bus address (so p2m) and then when unmapping the DMA we > >>> only get the bus address - so we needed to do a m2p lookup. > >> > >> OK, we need a m2p (that we already have in machine_to_phys_mapping), > >> what I don't understand is why we need the m2p override. > > > > The m2p is a host global table. > > > > For a foreign page grant mapped into the current domain the m2p will > > give you the foreign (owner) domain's p from the m, not the local one. > > Yes, you are completely right, then I have to figure out why blkback > works fine with this patch applied (or at least it seems to work fine).
blkback also works for me when testing a similar patch. I'm still confused. One thing with your proposed patch: I'm not sure that you're putting back the correct mfn. Adding Anthony to the thread. --msw -- 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/
