Re: [Xen-devel] [PATCH v5 4/4] x86/smp: do not use scratch_cpumask when in interrupt or exception context

[Jan Beulich <jbeulich@xxxxxxxx>]

On 26.02.2020 13:38, Roger Pau Monne wrote:
> Using scratch_cpumask in send_IPI_mask is not safe in IRQ or exception
> context because it can nest, and hence send_IPI_mask could be
> overwriting another user scratch cpumask data when used in such
> contexts.
> 
> Instead introduce a new cpumask to be used by send_IPI_mask, and
> disable interrupts while using it.

With this now apparently stale sentence dropped (easily done
while committing)

> Fallback to not using the scratch cpumask (and hence not attemping to
> optimize IPI sending by using a shorthand) when in IRQ or exception
> context. Note that the scratch cpumask cannot be used when
> non-maskable interrupts are being serviced (NMI or #MC) and hence
> fallback to not using the shorthand in that case, like it was done
> previously.
> 
> Fixes: 5500d265a2a8 ('x86/smp: use APIC ALLBUT destination shorthand when 
> possible')
> Reported-by: Sander Eikelenboom <linux@xxxxxxxxxxxxxx>
> Signed-off-by: Roger Pau Monné <roger.pau@xxxxxxxxxx>

Reviewed-by: Jan Beulich <jbeulich@xxxxxxxx>

Jan

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