On Mon, Jan 07, 2013 at 07:17:33AM +0000, Xu, Dongxiao wrote: > > -----Original Message----- > > From: Jan Beulich [mailto:[email protected]] > > Sent: Thursday, December 20, 2012 4:56 PM > > To: Xu, Dongxiao > > Cc: [email protected]; Konrad Rzeszutek Wilk; > > [email protected] > > Subject: RE: [Xen-devel] [PATCH] xen/swiotlb: Exchange to contiguous memory > > for map_sg hook > > > > >>> On 20.12.12 at 02:23, "Xu, Dongxiao" <[email protected]> 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. > > Sorry for the late response about this thread. > > To make sure I understand you correctly, so do you mean the correct fix > should be applied to libata driver, and make sure it DMA from/to correct > place (for example, some memory allocated by DMA API), but not such certain > field in a static structure?
Or with baremetal swiotlb if the user booted with 'swiotlb=force'. > > If we fix it in device driver side, then we may not need to modify the > xen-swiotlb part. > Correct. This is a bug in the device driver where it checks the contents of its buffer _before_ doing an DMA unmap or DMA sync. -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to [email protected] More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
