linux-kernel - Re: [PATCH v3 8/8] KVM: x86: avoid loading PDPTRs after migration when possible

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Message-ID: <289ac328-703f-6eb0-292e-99b1eda08784@redhat.com>
Date:   Sat, 19 Jun 2021 09:03:11 +0200
From:   Paolo Bonzini <pbonzini@...hat.com>
To:     Sean Christopherson <seanjc@...gle.com>,
        Maxim Levitsky <mlevitsk@...hat.com>
Cc:     kvm@...r.kernel.org, open list <linux-kernel@...r.kernel.org>,
        "open list:DOCUMENTATION" <linux-doc@...r.kernel.org>,
        Wanpeng Li <wanpengli@...cent.com>,
        Ingo Molnar <mingo@...hat.com>,
        Vitaly Kuznetsov <vkuznets@...hat.com>,
        Thomas Gleixner <tglx@...utronix.de>,
        Borislav Petkov <bp@...en8.de>, Joerg Roedel <joro@...tes.org>,
        "maintainer:X86 ARCHITECTURE (32-BIT AND 64-BIT)" <x86@...nel.org>,
        Jim Mattson <jmattson@...gle.com>,
        Jonathan Corbet <corbet@....net>,
        "H. Peter Anvin" <hpa@...or.com>
Subject: Re: [PATCH v3 8/8] KVM: x86: avoid loading PDPTRs after migration
 when possible

On 18/06/21 22:53, Sean Christopherson wrote:
> The bool is essentially an extension of
> KVM_REQ_GET_NESTED_STATE_PAGES, I think it makes sense to clear the flag whenever
> KVM_REQ_GET_NESTED_STATE_PAGES is cleared.

So in vcpu_enter_guest?

> Another thing that's not obvious is the required ordering between KVM_SET_SREGS2
> and KVM_SET_NESTED_STATE.  AFAICT it's not documented, but that may be PEBKAC on
> my end.  E.g. what happens if walk_mmu == &root_mmu (L1 active in targte KVM)
> when SET_SREGS2 is called, and_then_  KVM_SET_NESTED_STATE is called?

Either ordering should work.

Paolo