Re: [Qemu-devel] [PATCH] migration: avoid copying ignore-shared ramblock when in incoming migration

[Peter Maydell]

On Fri, 22 Mar 2019 at 10:12, Dr. David Alan Gilbert
<address@hidden> wrote:
> Right, so in Catherine's patch there's a simple in_incoming_migration
> and checking ramblock_is_ignored

Mmm, but I think it is in the wrong place. It is being checked
in address_space_write_rom_internal(). Either we want to
suppress any and all writes to these RAM blocks, in which
case I don't think that function covers all the ways that
code can get hold of a RAM block and write to it; or we are
confident that only the ROM blobs are an issue, in which
case it is too low in the call stack and we should do the
check in rom_reset().

Are there any other cases where we might write to RAM
during reset/migration ? I thought of "user write via
the debug stub or monitor", but perhaps those either
can't happen or we define them as user error. But I
there might be some other obscure cases, which perhaps
argues for doing this at the lowest level possible.

thanks
-- PMM