Re: ARM Snapshots Not Backwards-Compatible

[Peter Maydell]

On Wed, 3 Feb 2021 at 15:11, Dr. David Alan Gilbert <dgilbert@redhat.com> wrote:
> It's interesting that on x86 we've got a longterm request to *add* cpu
> features to the stream to detect screwups caused by using mismatched
> CPUs; so it's not necessarily a bad idea to include it once you realise
> it's there.

I think we would want to do that by checking the ID registers,
not the legacy ad-hoc feature-flags word. In fact I think for
KVM at least we already perform the check on the ID registers,
in that the kernel will return an error if we pass it a value
for an ID register and it's not the value it should be.
I forget whether we try to check this for TCG (the mechanism
for handling sysreg migration there is different).

As a side note I suspect that the first two issues Aaron ran
into are TCG-only and don't affect KVM.

thanks
-- PMM