Re: [SeaBIOS] varlow/extrastack vs code

[Paolo Bonzini]

On 14/02/2017 22:50, Gerd Hoffmann wrote:
> Hi,
> > Just for historical perspective - the reason I think qemu didn't
> > implement the pam "read from rom and write to memory" mode is that I
> > don't think there's a good way to emulate that with page tables (and
> > the range needs to be executable so just making it all device memory
> > isn't practical).
>
> A while back kvm got support for memory slots which allow read access
> and vmexit on write access.  Flash emulation needs this, and I think it
> is possible to also implement the "read from rom and write to memory"
> mode using that.

It would be very slow of course, but if the only writes are to
TimerLast, perhaps that would work?

Paolo