Re: [Xen-devel] [PATCH v4 6/6] x86/microcode: Synchronize late microcode loading

["Jan Beulich" <JBeulich@xxxxxxxx>]

>>> On 29.11.18 at 23:43, <boris.ostrovsky@xxxxxxxxxx> wrote:
> One other comment about this patch (which IIRC was raised by Andrew on
> an earlier version) is that it may be worth to stop timer calibration. I
> am pretty sure we've seen deadlocks, which is why we ended up disabling
> it during microcode updates.

I recall the claim, but I don't think I've ever seen proof. My point was
ans still is that if there's a problem with ucode loading using the
stop-machine logic here, then there's a problem with the stop-machine
logic in general, which would make other uses, perhaps most notably
rcu_barrier(), unsafe too. Otoh from your reply it's not clear whether
the observed issue wasn't with our present way of loading ucode,
but then it would put under question the general correctness of
continue_hypercall_on_cpu(), which again we use for more than just
ucode loading.

Jan



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