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

[Jan Beulich <jbeulich@xxxxxxxx>]

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)?

Jan

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