[lkml]   [2013]   [Nov]   [5]   [last100]   RSS Feed
Views: [wrap][no wrap]   [headers]  [forward] 
Messages in this thread
SubjectRe: [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
To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to
More majordomo info at
Please read the FAQ at

 \ /
  Last update: 2013-11-05 16:21    [W:0.083 / U:4.732 seconds]
©2003-2020 Jasper Spaans|hosted at Digital Ocean and TransIP|Read the blog|Advertise on this site