Re: [Qemu-devel] [RFC PATCH] QEMU may write to system_memory before guest starts

[Dr. David Alan Gilbert]

* Peter Maydell (address@hidden) wrote:
> On Tue, 19 Mar 2019 at 11:03, Dr. David Alan Gilbert
> <address@hidden> wrote:
> >
> > * Peter Maydell (address@hidden) wrote:
> > > I didn't think migration distinguished between "main memory"
> > > and any other kind of RAMBlock-backed memory ?
> >
> > In Yury's case there's a distinction between RAMBlock's that are mapped
> > with RAM_SHARED (which normally ends up as MAP_SHARED) and all others.
> > You can set that for main memory by using -numa to specify a memdev
> > that's backed by a file and has the share=on property.
> >
> > On x86 the ROMs end up as separate RAMBlock's that aren't affected
> > by that -numa/share=on - so they don't fight Yury's trick.
> 
> You can use the generic loader on x86 to load an ELF file
> into RAM if you want, which would I think also trigger this.

OK, although that doesn't worry me too much  - since in the majority
of cases Yury's trick still works well.

I wonder if there's a way to make Yury's code to detect these cases
and not allow the feature;  the best thing for the moment would seem to
be to skip the aarch test that uses elf loading.

Dave

> thanks
> -- PMM
--
Dr. David Alan Gilbert / address@hidden / Manchester, UK