linux-kernel - Re: [PATCH v2 06/10] KVM: x86: acknowledgment mechanism for async pf page ready notifications

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Date:   Thu, 28 May 2020 13:44:12 +0200
From:   Paolo Bonzini <pbonzini@...hat.com>
To:     Vitaly Kuznetsov <vkuznets@...hat.com>, kvm@...r.kernel.org,
        x86@...nel.org
Cc:     Andy Lutomirski <luto@...nel.org>,
        Thomas Gleixner <tglx@...utronix.de>,
        Borislav Petkov <bp@...en8.de>,
        "H. Peter Anvin" <hpa@...or.com>,
        Wanpeng Li <wanpengli@...cent.com>,
        Sean Christopherson <sean.j.christopherson@...el.com>,
        Jim Mattson <jmattson@...gle.com>,
        Vivek Goyal <vgoyal@...hat.com>, Gavin Shan <gshan@...hat.com>,
        Peter Zijlstra <peterz@...radead.org>,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH v2 06/10] KVM: x86: acknowledgment mechanism for async pf
 page ready notifications

On 28/05/20 13:39, Vitaly Kuznetsov wrote:
>> How is the pageready_pending flag migrated?  Should we revert the
>> direction of the MSR (i.e. read the flag, and write 0 to clear it)?
> The flag is not migrated so it will be 'false'. This can just cause an
> extra kick in kvm_arch_async_page_present_queued() but this shouldn't be
> a big deal. Also, after migration we will just send 'wakeup all' event,
> async pf queue will be empty.

Ah, that's kvm_pv_enable_async_pf, where the destination writes to
MSR_KVM_ASYNC_PF.  Cool.

> MSR_KVM_ASYNC_PF_ACK by itself is not
> migrated, we don't even store it, not sure how invering it would change
> things.

Yes, it would only be useful to invert it if it needs to be stored and
migrated.

Thanks,

Paolo