Re: [Xen-devel] [PATCH] libxc/restore: Don't duplicate state in process_vcpu_basic()

[Ian Jackson <ian.jackson@xxxxxxxxxx>]

Andrew Cooper writes ("Re: [PATCH] libxc/restore: Don't duplicate state in 
process_vcpu_basic()"):
> On 20/12/2019 18:22, Ian Jackson wrote:
> > It is not obvious to me that nothing uses the modified fields after
> > process_vcpu_basic has edited things.  The ctx of which the vcpu is
> > part is passed to process_vcpu_<various> by update_vcpu_context.
...
> Yes.  It was a consequence of adding Remus support (which happened on
> xen-devel, post actually-getting-migration-v2-working).
> 
> Originally, this was copied out of the incoming xc_sr_record* pointer
> which was const.  Adding Remus support required buffering these records
> on each checkpoint, which is why they are stashed sideways now.
> 
> By the time we get process_vcpu_basic(), we are committed to completing
> state restoration and unpausing the guest.
> 
> In particular, it is not possible to process any further memory pages
> because the hypercall used here changes typerefs on pagetables, which
> makes them immutable from the toolstacks point of view (technically not,
> but we can't map them and memcpy them any more).

Thanks for the explanation.  Can you add that to the commit message
please ?  That way if this turns out to be wrong, or someone wants to
revert it again, we'll have some record of why this was thought to be
OK.

With that done,

Acked-by: Ian Jackson <ian.jackson@xxxxxxxxxxxxx>

Thanks,
Ian.

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