On 29/02/2016 13:56, Christoph Hellwig wrote:

On Mon, Feb 29, 2016 at 01:35:44PM +0200, Sagi Grimberg wrote:

quoted

quoted

But for lager SG entries we need it to calculate the correct
base address.

I'm not sure if this is true either. Can you explain why?

Assume we get a SG entry that is exactly 2 pages (8k) long.  But we
also have an offset of 6k into it, so we need to skip into the
second page to make the following work:

quoted

The Memory region mapping is described by:
1. page vector: [addr0, addr1, addr2,...]
2. iova: the first byte offset
3. length: the total byte count of the mr
4. page_size: size of each page in the page vector

This means that the HCA assumes that each address in
the page vector has the size of page_size, also the region
can start at some offset (iova - addr0), and it has some length.

Exactly.

For the above case we don't need the page at sg_dma_address(), though.
We need the one after it, so we need to make sure the page address
is calculated for the second page in the SG entry.

If we add sg_offset to dma_addr is in my page this means we get the
right page address from this line:

		u64 page_addr = dma_addr & page_mask;

without that's we'd get the address of the first page, which doesn't
actually contain any data we want to map.

Yea, makes sense...

I get it now! Thanks!