Re: [Xen-devel] [PATCH 2/3] x86/smp: use a dedicated scratch cpumask in send_IPI_mask

[Jan Beulich <jbeulich@xxxxxxxx>]

On 12.02.2020 17:49, Roger Pau Monne wrote:
> Using scratch_cpumask in send_IPI_mak is not safe because it can be
> called from interrupt context, and hence Xen would have to make sure
> all the users of the scratch cpumask disable interrupts while using
> it.
> 
> Instead introduce a new cpumask to be used by send_IPI_mask, and
> disable interrupts while using.

My first thought here was: What about NMI or #MC context? Even if
not using the function today (which I didn't check), there shouldn't
be a latent issue introduced here preventing them from doing so in
the future. Instead I think you want to allocate the scratch mask
dynamically (at least if caller context doesn't allow use of the
generic one), and simply refrain from coalescing IPIs if this
allocations fails.

Jan

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