Re: [Qemu-devel] QEMU commit 04bf2526ce breaks use of xen-mapcache

[Stefano Stabellini]

On Tue, 25 Jul 2017, Paolo Bonzini wrote:
> > Hi,
> > 
> > Commits 04bf2526ce (exec: use qemu_ram_ptr_length to access guest ram)
> > start using qemu_ram_ptr_length() instead of qemu_map_ram_ptr().
> > That result in calling xen_map_cache() with lock=true, but this mapping
> > is never invalidated.
> > So QEMU use more and more RAM until it stop working for a reason or an
> > other. (crash if host have little RAM or stop emulating but no crash)
> > 
> > I don't know if calling xen_invalidate_map_cache_entry() in
> > address_space_read_continue() and address_space_write_continue() is the
> > right answer.  Is there something better to do ?
> 
> I think it's correct for dma to be true... maybe add a lock argument to
> qemu_ram_ptr_length, so that make address_space_{read,write}_continue can
> pass 0 and everyone else passes 1?

I think that is a great suggestion. That way, the difference between
locked mappings and unlocked mappings would be explicit, rather than
relying on callers to use qemu_map_ram_ptr for unlocked mappings and
qemu_ram_ptr_length for locked mappings. And there aren't that many
callers of qemu_ram_ptr_length, so adding a parameter wouldn't be an
issue.