On 29/02/2016 13:56, Christoph Hellwig wrote:
On Mon, Feb 29, 2016 at 01:35:44PM +0200, Sagi Grimberg wrote:
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:
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!
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