linux-kernel - Re: [PATCH v2 02/10] KVM: x86: extend struct kvm_vcpu_pv_apf

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Date:   Thu, 28 May 2020 12:59:53 +0200
From:   Paolo Bonzini <pbonzini@...hat.com>
To:     Vitaly Kuznetsov <vkuznets@...hat.com>,
        Vivek Goyal <vgoyal@...hat.com>
Cc:     kvm@...r.kernel.org, x86@...nel.org,
        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>,
        Gavin Shan <gshan@...hat.com>,
        Peter Zijlstra <peterz@...radead.org>,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH v2 02/10] KVM: x86: extend struct kvm_vcpu_pv_apf_data
 with token info

On 28/05/20 10:42, Vitaly Kuznetsov wrote:
> How does it work with the patchset: 'page not present' case remains the
> same. 'page ready' case now goes through interrupts so it may not get
> handled immediately. External interrupts will be handled by L0 in host
> mode (when L2 is not running). For the 'page ready' case L1 hypervisor
> doesn't need any special handling, kvm_async_pf_intr() irq handler will
> work correctly.
> 
> I've smoke tested this with VMX and nothing immediately blew up.

Indeed.

It would be an issue in the remote (read: nonexistent) case of a
hypervisor that handles async page faults and does not VMEXIT on
interrupts.  In this case it would not be able to enable page ready as
interrupt, and it would have to get rid of async page fault support.

Paolo