Messages in this thread | | | Date | Thu, 20 Dec 2012 08:56:17 +0000 | From | "Jan Beulich" <> | Subject | RE: [Xen-devel] [PATCH] xen/swiotlb: Exchange to contiguous memory for map_sg hook |
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>>> On 20.12.12 at 02:23, "Xu, Dongxiao" <dongxiao.xu@intel.com> wrote: > Sorry, maybe I am still not describing this issue clearly.
No, at least I understood you the way you re-describe below.
> Take the libata case as an example, the static DMA buffer locates > (dev->link->ap->sector_buf , here we use Data Structure B in the graph) in > the following structure: > > -------------------------------------Page boundary > <Data Structure A> > <Data Structure B> > -------------------------------------Page boundary > <Data Structure B (cross page)> > <Data Structure C> > -------------------------------------Page boundary > > Where Structure B is our DMA target. > > For Data Structure B, we didn't care about the simultaneous access, either > lock or sync function will take care of it. > What we are not sure is "read/write of A and C from other processor". As we > will have memory copy for the pages, and at the same time, other CPU may > access A/C.
The question is whether what libata does here is valid in the first place - fill an SG list entry with something that crosses a page boundary and is not a compound page.
Jan
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