On Wed, Nov 04, 2020 at 09:42:41AM -0400, Jason Gunthorpe wrote:
> On Wed, Nov 04, 2020 at 10:50:49AM +0100, Christoph Hellwig wrote:
>
> > +int ib_dma_virt_map_sg(struct ib_device *dev, struct scatterlist *sg, int
> > nents)
> > +{
> > + struct scatterlist *s;
> > + int i;
> > +
> > + for_each_sg(sg, s, nents, i) {
> > + sg_dma_address(s) = (uintptr_t)sg_virt(s);
> > + sg_dma_len(s) = s->length;
>
> Hmm.. There is nothing ensuring the page is mapped here for this
> sg_virt(). Before maybe some of the kconfig stuff prevented highmem
> systems indirectly, I wonder if we should add something more direct to
> exclude highmem for these drivers?
I had actually noticed this earlier as well and then completely forgot
about it..
rdmavt depends on X86_64, so it can't be used with highmem, but for
rxe and siw there weren't any such dependencies so I think we were just
lucky. Let me send a fix to add explicit depencies and then respin this
series on top of that..
> Sigh. I think the proper fix is to replace addr/length with a
> scatterlist pointer in the struct ib_sge, then have SW drivers
> directly use the page pointer properly.
The proper fix is to move the DMA mapping into the RDMA core, yes.
And as you said it will be hard. But I don't think scatterlists
are the right interface. IMHO we can keep re-use the existing
struct ib_sge:
struct ib_ge {
u64 addr;
u32 length;
u32 lkey;
};
with the difference that if lkey is not a MR, addr is the physical
address of the memory, not a dma_addr_t or virtual address.
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