Re: [PATCH v2] KVM: SVM: use vmsave/vmload for saving/restoring additional host state

Michael Roth
2020-12-15T18:58:13Z

Hi Sean,

Sorry to reply out-of-thread, our mail server is having issues with
certain email addresses at the moment so I only see your message via
the archives atm. But regarding:

>>> I think we can defer this until we're actually planning on running
>>> the guest,
>>> i.e. put this in svm_prepare_guest_switch().
>>
>> It looks like the SEV-ES patches might land before this one, and those
>> introduce similar handling of VMSAVE in svm_vcpu_load(), so I think it
>> might also create some churn there if we take this approach and want
>> to keep the SEV-ES and non-SEV-ES handling similar.
>
>Hmm, I'll make sure to pay attention to that when I review the SEV-ES
>patches,
>which I was hoping to get to today, but that's looking unlikely at this
>point.

It looks like SEV-ES patches are queued now. Those patches have
undergone a lot of internal testing so I'm really hesitant to introduce
any significant change to those at this stage as a prereq for my little
patch. So for v3 I'm a little unsure how best to approach this.

The main options are:

a) go ahead and move the vmsave handling for non-sev-es case into
prepare_guest_switch() as you suggested, but leave the sev-es where
they are. then we can refactor those as a follow-up patch that can be
tested/reviewed as a separate series after we've had some time to
re-test, though that would probably just complicate the code in the
meantime...

b) stick with the current approach for now, and consider a follow-up series
to refactor both sev-es and non-sev-es as a whole that we can test
separately.

c) refactor SEV-ES handling as part of this series. it's only a small change
to the SEV-ES code but it re-orders enough things around that I'm
concerned it might invalidate some of the internal testing we've done.
whereas a follow-up refactoring such as the above options can be rolled
into our internal testing so we can let our test teams re-verify

Obviously I prefer b) but I'm biased on the matter and fine with whatever
you and others think is best. I just wanted to point out my concerns with
the various options.

-Mike