linux-kernel - Re: [RFC PATCH 0/2] Mitigating Excessive Pause-Loop Exiting in VM-Agnostic KVM

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Message-Id: <20210426031858.12003-1-kentaishiguro@sslab.ics.keio.ac.jp>
Date:   Mon, 26 Apr 2021 12:18:58 +0900
From:   Kenta Ishiguro <kentaishiguro@...ab.ics.keio.ac.jp>
To:     kernellwp@...il.com
Cc:     david@...hat.com, jmattson@...gle.com, joro@...tes.org,
        kentaishiguro@...ab.ics.keio.ac.jp, kono@...ab.ics.keio.ac.jp,
        kvm@...r.kernel.org, linux-kernel@...r.kernel.org,
        pbonzini@...hat.com, pl@...ab.ics.keio.ac.jp, seanjc@...gle.com,
        vkuznets@...hat.com, wanpengli@...cent.com
Subject: Re: [RFC PATCH 0/2] Mitigating Excessive Pause-Loop Exiting in VM-Agnostic KVM

Thank you for the reply.

My question is about following scenario:
1. running vCPU receives IPI and the vCPU's ipi_received gets true
2. the vCPU responds to the IPI
3. the vCPU exits
4. the vCPU is preempted by KVM
5. the vCPU is boosted, but it has already responded to the IPI
6. the vCPU enters and the vCPU's ipi_received is cleaned

In this case, I think the check of vcpu->preempted does not limit the candidate vCPUs.