Re: [Xen-devel] [PATCH] xen/x86: vpmu: Unmap per-vCPU PMU page when the domain is destroyed

[Julien Grall <jgrall@xxxxxxxxxx>]

Hi,

On 27/11/2019 09:44, Jan Beulich wrote:
> On 26.11.2019 18:17, Paul Durrant wrote:
> > From: Julien Grall <jgrall@xxxxxxxxxx>
> >
> > A guest will setup a shared page with the hypervisor for each vCPU via
> > XENPMU_init. The page will then get mapped in the hypervisor and only
> > released when XEMPMU_finish is called.
> >
> > This means that if the guest is not shutdown gracefully (such as via xl
> > destroy), the page will stay mapped in the hypervisor.
> Isn't this still too weak a description? It's not the tool stack
> invoking XENPMU_finish, but the guest itself afaics. I.e. a
> misbehaving guest could prevent proper cleanup even with graceful
> shutdown.
>
> > @@ -2224,6 +2221,9 @@ int domain_relinquish_resources(struct domain *d)
> >       if ( is_hvm_domain(d) )
> >           hvm_domain_relinquish_resources(d);
> >   
> > +    for_each_vcpu ( d, v )
> > +        vpmu_destroy(v);
> > +
> >       return 0;
> >   }
> I think simple things which may allow shrinking the page lists
> should be done early in the function. As vpmu_destroy() looks
> to be idempotent, how about leveraging the very first
> for_each_vcpu() loop in the function (there are too many of them
> there anyway, at least for my taste)?
This is not entirely obvious that vpmu_destroy() is idempotent.

For instance, I can't find out who is clearing VCPU_CONTEXT_ALLOCATED. 
so I think vcpu_arch_destroy() would be executed over and over.
I don't know whether this is an issue, but I can't figure out that is it 
not one. Did I miss anything?
Cheers,

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