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Date: Tue, 5 Nov 2013 16:01:50 +0100 From: Roger Pau Monné <roger.pau@...rix.com> To: Konrad Rzeszutek Wilk <konrad.wilk@...cle.com> CC: David Vrabel <david.vrabel@...rix.com>, <xen-devel@...ts.xen.org>, <linux-kernel@...r.kernel.org>, Matt Wilson <msw@...zon.com> Subject: Re: [PATCH] grant-table: don't set m2p override if kmap_ops is not set 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. With this patch the m2p is correctly provided by mfn_to_pfn_no_overrides just by using the machine_to_phys_mapping array, why we need to add an override? -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@...r.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
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