Re: [PATCH v6 1/3] memory: drop guest writes to read-only ram device regions

[Yan Zhao <yan.y.zhao@intel.com>]

On Thu, May 21, 2020 at 04:38:47PM +0200, Paolo Bonzini wrote:
> On 30/04/20 11:40, Peter Maydell wrote:
> >> This does not "drop" a write to a r/o region -- it causes it to generate
> >> whatever the guest architecture's equivalent of a bus error is (eg data
> >> abort on Arm).
> 
> 
> > More generally, this change seems a bit odd: currently we do not
> > check the mr->readonly flag here, but in general guests don't get
> > to write to ROM areas. Where is that check currently done
> 
> Writes to ROM are directed to mr->ops unassigned_mem_ops.  Because _all_
> ram-device reads and writes go through the ops, for ram-device we have
> to stick the check for mr->readonly in the ops.
> 
> On one hand, I was quite surprised to see that unassigned_mem_write does
> not return MEMTX_ERROR now that I looked at it.
> 
> On the other hand, we should use MEMTX_ERROR in patch 2 as well, if we
> decide it's the way to go.
> 
> (Sorry Yan for the late response).
> 
hi Paolo,
thanks for your reply and never mind :)

But there's one thing I just can't figure out the reason and eagerly need
your guide.

why do we have to convert all .write operations to .write_with_attrs and
return MEMTX_ERROR? because of the handling of writes to read-only region?

however, it seems that all regions have to handle this case, so ultimately
we have to convert all .write to .write_with_attrs and there would be no
.write operations any more?

Thanks
Yan