Re: [RFC PATCH v2 05/23] KVM: arm: Add arch vcpu uninit hook

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On Fri, Nov 02, 2018 at 09:05:36AM +0100, Christoffer Dall wrote:
> On Fri, Sep 28, 2018 at 02:39:09PM +0100, Dave Martin wrote:
> > In preparation for adding support for SVE in guests on arm64, a
> > hook is needed for freeing additional per-vcpu memory when a vcpu
> > is freed.
> 
> Can this commit motivate why we can't do the work in kvm_arch_vcpu_free,
> which we use for freeing other data structures?
> 
> (Presumably, uninit is needed when you need to do something at the very
> last step after releasing the struct pid.

It wasn't to do with that.

Rather, the division of responsibility between the vcpu_uninit and
vcpu_free paths is not very clear.

In the earlier version of the series, I think SVE state may have been
allocated rather early and we may have needed to free it in the failure
path of kvm_arch_vcpu_create() (which just calls kvm_vcpu_uninit()).
(Alternatively, I may just have been wrong.)

Now, the vcpu must be fully created before the KVM_ARM_SVE_CONFIG ioctl
on it (which is what allocates sve_state) can succeed anyway.

So the distinction between these two teardown phases is probably no
longer important.

I'll see whether I can get rid of this hook and free the SVE state in
kvm_arch_vcpu_free() instead.

Does that make sense?

Cheers
---Dave
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