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SubjectRe: [PATCH] KVM/x86: Do not clear SIPI while in SMM
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On 4/16/24 22:47, Boris Ostrovsky wrote:
> When a processor is running in SMM and receives INIT message the interrupt
> is left pending until SMM is exited. On the other hand, SIPI, which
> typically follows INIT, is discarded. This presents a problem since sender
> has no way of knowing that its SIPI has been dropped, which results in
> processor failing to come up.
>
> Keeping the SIPI pending avoids this scenario.

This is incorrect - it's yet another ugly legacy facet of x86, but we
have to live with it. SIPI is discarded because the code is supposed to
retry it if needed ("INIT-SIPI-SIPI").

The sender should set a flag as early as possible in the SIPI code so
that it's clear that it was not received; and an extra SIPI is not a
problem, it will be ignored anyway and will not cause trouble if there's
a race.

What is the reproducer for this?

Paolo


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