Re: ARM Snapshots Not Backwards-Compatible

[Aaron Lindsay]

On Feb 03 15:26, Peter Maydell wrote:
> 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).

Ah, I sent my reply where I mentioned attempting to find a way to
selectively check env.features before I saw this. I'll just send the
patch for `VMSTATE_UNUSED(sizeof(uint64_t))`.

-Aaron