Re: [PATCH for-next v2 06/18] RDMA/rxe: Add rxe_add_frag() to rxe_mr.c

Jason Gunthorpe
2022-12-01T12:51:30Z

On Wed, Nov 30, 2022 at 11:05:04PM -0600, Bob Pearson wrote:
> On 11/30/22 18:41, Jason Gunthorpe wrote:
> > On Wed, Nov 30, 2022 at 06:36:56PM -0600, Bob Pearson wrote:
> >> I'm not looking at my patch you responded to but the one you posted to replace maps
> >> by xarrays.
> >
> > I see, I botched that part
> >
> >> The existing rxe driver assumes that if ibmr->type == IB_MR_TYPE_DMA
> >> that the iova is just a kernel (virtual) address that is already
> >> mapped.
> >
> > No, it is not correct
> >
> >> Maybe this is not correct but it has always worked this way. These
> >> are heavily used by storage stacks (e.g. Lustre) which always use
> >> DMA mr's. Since we don't actually do any DMAs we don't need to setup
> >> the iommu for these and just do memcpy's without dealing with pages.
> >
> > You still should be doing the kmap
> >
> > Jason
>
> Does this have to do with 32 bit machines? I have always tested on 64 bit machines and
> dma mr's are always already mapped.

Originally, but people are making 64 bit machines require kmap for
security purposes

Jason