ion: return a fresh sg_table from ion_map_dma_buf

DMA mappers often (always?) modify the scatterlist they are
given (e.g. dma_address and dma_length) when their dma_map_ops.map_sg
operation is called.  Currently Ion always returns the same sg_table
when it's dma_buf_ops.map_dma_buf operation is called.  The result is
that when Ion is used as a DMA buf exporter to multiple clients (a
common scenario during zero-copy buffer-sharing) those clients will be
stomping all over each other since they're both trying to put their
mappings into the same sg_table.

Fix this by always duplicating the buffer's sg_table in ion_map_dma_buf
and returning the duplicate.  Each buffer will still always have a
single "master" sg_table that should never be exported to the DMA buf
framework.

Test case (pseudo-code):

    handle = ion_alloc();
    dbuf = ion_share_dma_buf(handle);
    attach = dma_buf_attach(dbuf);
    table1 = dma_buf_map_attachment(attach);
    table2 = dma_buf_map_attachment(attach);
    dma_map_sg(table1);
    table2 = dma_buf_map_attachment(attach);
    dma_map_sg(table2);
    /* table1 is now hosed */
    check_mappings(table1); /* KABOOM */

Change-Id: Ifefa06ecd464c00819b4ae7ac32ad37f1491373b
Signed-off-by: Mitchel Humpherys <mitchelh@codeaurora.org>

0 files changed, 0 insertions, 0 deletions