Re: [Xen-devel] [PATCH v3] x86/AMD: Add support for AMD's OSVW feature in guests

["Jan Beulich" <JBeulich@xxxxxxxx>]

>>> On 31.01.12 at 20:16, Boris Ostrovsky <boris.ostrovsky@xxxxxxx> wrote:
> @@ -502,6 +503,20 @@ long do_domctl(XEN_GUEST_HANDLE(xen_domc
>          /* Needed, for example, to ensure writable p.t. state is synced. */
>          domain_pause(d);
>  
> +        /* 
> +         * Certain operations (e.g. CPU microcode updates) modify data which 
> is
> +         * used during VCPU allocation/initialization
> +         */
> +        while ( !spin_trylock(&vcpu_alloc_lock) )
> +            if ( hypercall_preempt_check() )
> +            {
> +                ret =  hypercall_create_continuation(
> +                    __HYPERVISOR_domctl, "h", u_domctl);
> +                domain_unpause(d);
> +                rcu_unlock_domain(d);
> +                break;

This "break" will only get you out of the while() loop, falling through
into the immediately following code (without holding the lock), which
is not what you want afaict.

Jan

> +            }
> +
>          /* We cannot reduce maximum VCPUs. */
>          ret = -EINVAL;
>          if ( (max < d->max_vcpus) && (d->vcpu[max] != NULL) )



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