Re: [PATCH v6 1/4] memory: prevent dma-reentracy issues

[Alexander Bulekov]

On 230310 1245, Peter Maydell wrote:
> On Fri, 10 Mar 2023 at 12:32, Alexander Bulekov <alxndr@bu.edu> wrote:
> > This MR seems to be "lsi-ram".
> >
> > From hw/scsi/lsi53c895a.c:
> >
> > memory_region_init_io(&s->ram_io, OBJECT(s), &lsi_ram_ops, s,
> >         "lsi-ram", 0x2000);
> >
> > So the LSI device is reading an LSI "Script" from its own IO region.. In
> > this particular case, I think there was no reason to use
> > memory_region_init_io rather than memory_region_init_ram, but this makes
> > me worried that there are other devices that use something like this.
> 
> This particular device predates the entire MemoryRegion set of
> abstractions, so it might have seemed easier at the time.
> The endianness handling of the current code is also a bit
> confusing and might make it tricky to convert to a RAM MR.

With my trivial mr_io - > mr_ram conversion, I no longer hit the
re-entrancy tracepoint, and my livecd boots, but it's probably not
exhaustively using the script functionality.. 

Does the endianness actually cause a problem? As long as all accesses
(CPU -> LSI_RAM and LSI -> LSI_RAM) occur through the address_space API,
are we safe?
-Alex