Re: [PATCH] KVM/x86: Do not clear SIPI while in SMM

[Paolo Bonzini <pbonzini@redhat.com>]

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