Messages in this thread |  | | Date | Tue, 5 Nov 2013 17:03:58 +0100 | From | Roger Pau Monné <> | Subject | Re: [Xen-devel] [PATCH] grant-table: don't set m2p override if kmap_ops is not set |
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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).
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