On Thu, Sep 10, 2020 at 10:21:07AM +0100, Steven Price wrote:

quoted

We either need a KVM cap or a new CPU feature probing interface to avoid
making userspace try features one at a time. It's too bad that VCPU_INIT
doesn't clear all offending features from the feature set when returning
EINVAL, because then userspace could create a scratch VCPU with everything
it supports in order to see what KVM also supports in one go.

If Peter's TELL_ME_WHAT_YOU_HAVE idea works out then perhaps we don't need
the cap? Or would it still be useful?

We wouldn't need it, but we don't _need_ it now either. It's not very
convenient to probe vcpu features with scratch vcpus, especially if we
must probe one at a time, but it works. The TELL_ME_WHAT_YOU_HAVE idea
will only fix the one at a time issue, but still require a vcpu fd. If
this feature becomes a VM feature then a cap or VM level API would help
reduce the userspace probing work.

Thanks,
drew


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