Re: [Xen-devel] [PATCH] xen/sched: Introduce domain_vcpu() helper

[Wei Liu <wei.liu2@xxxxxxxxxx>]

On Wed, Jan 23, 2019 at 02:59:29PM +0000, Andrew Cooper wrote:
> The progression of multi-vcpu support in Xen (originally a single pointer,
> then an embedded d->vcpu[] array, then a dynamically allocated array) has
> resulted in a large quantity of ad-hoc code for looking a vcpu up by id, and a
> large number of ways that the toolstack can cause Xen to trip over a NULL
> pointer.  Some of this has been addressed in Xen 4.12, and work is ongoing.
> 
> Another property of looking a vcpu up by id is frequently done in unprivileged
> hypercall context, making it an attractive target for speculative sidechannel
> attacks.
> 
> Introduce a helper to do the lookup correctly, and without speculative
> interference.  For performance reasons, it is useful not to have an smp_rmb()
> in this helper on ARM, and luckily this is safe to do, because of the
> serialisation offered by the global domheap lock.

I think you mean domlist lock here?

Wei.

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