linux-kernel - Re: [RFC PATCH] KVM: race-free exit from KVM

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Message-ID: <8da58a9f-5de6-d2af-559d-4b04201f0d87@redhat.com>
Date:   Wed, 8 Feb 2017 15:10:24 +0100
From:   Paolo Bonzini <pbonzini@...hat.com>
To:     Christian Borntraeger <borntraeger@...ibm.com>,
        linux-kernel@...r.kernel.org, kvm@...r.kernel.org
Subject: Re: [RFC PATCH] KVM: race-free exit from KVM_RUN without POSIX
 signals



On 08/02/2017 14:18, Christian Borntraeger wrote:
>>           VCPU thread                     service thread
>>    --------------------------------------------------------------
>>                                           raise signal
>>         signal handler
>>           set run->immediate_exit
>>         KVM_RUN
>>           check run->immediate_exit
> So the idea is to have both, a signal and this flag and you want userspace
> to set this flag in its signal handler?

Yes.  This flag can also replace qemu_cpu_kick_self.

> So we no longer block this signal
> in QEMU then. Makes sense.
> Do you have the QEMU patch ready, to do a better review of the whole idea?

I have something that seems to work, but I've not stressed it at all and
it depends on a few cleanups to the SIGBUS handling code (which is
currently x86-specific).

Paolo