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[Qemu-devel] [PATCH 0/2 version 2] fw_cfg: Implement fast "DMA"-type ope

From: Richard W.M. Jones
Subject: [Qemu-devel] [PATCH 0/2 version 2] fw_cfg: Implement fast "DMA"-type operation for rapidly copying in kernel, initrd [etc] into the guest
Date: Mon, 19 Jul 2010 11:15:04 +0100
User-agent: Mutt/1.5.18 (2008-05-17)

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

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

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 ...


Richard Jones, Virtualization Group, Red Hat http://people.redhat.com/~rjones
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