Re: [Qemu-devel] [PATCH 2/2 v2][UPDATED] Direct IDE I/O

[Paul Brook]

On Monday 17 December 2007, Fabrice Bellard wrote:
> Laurent Vivier wrote:
> > This patch enhances the "-drive ,cache=off" mode with IDE drive emulation
> > by removing the buffer used in the IDE emulation.
> > ---
> >  block.c     |   10 +++
> >  block.h     |    2
> >  block_int.h |    1
> >  cpu-all.h   |    1
> >  exec.c      |   19 ++++++
> >  hw/ide.c    |  176
> > +++++++++++++++++++++++++++++++++++++++++++++++++++++++++--- vl.c       
> > |    1
> >  7 files changed, 204 insertions(+), 6 deletions(-)
> > [...]
>
> Unfortunately it is more complicated to write to the CPU memory. In
> particular, specific action should be done when translated code is
> present. A consistent API must include something like cpu_page_lock() /
> unlock(). Look at cpu_physical_memory_rw() to see the various issues
> which must be handled. Moreover, it would be better to add bus specific
> APIs (at least for PCI), but I can accept a CPU memory API for now.

In general it may also be unsafe to do async writes directly to guest memory 
because you break the atomicity of loads/stores.

Paul