[Qemu-devel] [PATCH 0/2 version 2] fw_cfg: Implement fast "DMA"-type operation for rapidly copying in kernel, initrd [etc] into the guest

[Richard W.M. Jones]

This is the second version of the patch.

We don't use the word "blit" any more, instead this is replaced with
"DMA", even though it's not quite like a DMA operation on physical
hardware.

The guest writes the physical address and size to two 32 bit fw_cfg
variables.  Then when the guest issues an ordinary read operation with
the extra FW_CFG_DMA flag set, instead of returning a single byte,
qemu "DMA"s the requested data into the guest memory.

The guest shouldn't be able to request a dma_size larger than the
amount of data in the entry.  The patch checks this and adjusts
dma_size.

The guest might select a dma_addr which does not correspond to
physical memory (or dma_addr + dma_size).  Reading the code it seems
to be that cpu_physical_memory_write catches this case and will
abort() (so the guest is only harming itself).  However I'd quite like
an expert opinion on this ...

Rich.

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