linux-kernel - Re: [PATCH 4/7] KVM: nVMX: move inject_page_fault tweak to .complete_mmu

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Message-ID: <eaa92c4a-79c1-8a12-9742-1c9007b63e23@redhat.com>
Date:   Thu, 18 Feb 2021 10:45:44 +0100
From:   Paolo Bonzini <pbonzini@...hat.com>
To:     Maxim Levitsky <mlevitsk@...hat.com>,
        Sean Christopherson <seanjc@...gle.com>
Cc:     kvm@...r.kernel.org, linux-kernel@...r.kernel.org,
        Wanpeng Li <wanpengli@...cent.com>,
        Borislav Petkov <bp@...en8.de>, Joerg Roedel <joro@...tes.org>,
        Jim Mattson <jmattson@...gle.com>,
        "H. Peter Anvin" <hpa@...or.com>,
        "maintainer:X86 ARCHITECTURE (32-BIT AND 64-BIT)" <x86@...nel.org>,
        Thomas Gleixner <tglx@...utronix.de>,
        Vitaly Kuznetsov <vkuznets@...hat.com>,
        Ingo Molnar <mingo@...hat.com>
Subject: Re: [PATCH 4/7] KVM: nVMX: move inject_page_fault tweak to
 .complete_mmu_init

On 17/02/21 19:43, Maxim Levitsky wrote:
> 1. npt/ept disabled in the host. In this case we have a single shadowing
> and a nested hypervisor has to do its own shadowing on top of it.
> In this case the MMU itself has to generate page faults (they are a result
> of hardware page faults, but are completely different), and in case
> of nesting these page faults have to be sometimes injected as VM exits.
> 
> [...] Also if the emulator injects the page fault, then indeed I think the
> bug will happen.

But in both cases you (ought to) get an injected exception which then 
becomes a page fault vmexit at next check_nested_events.  That's the 
part that we are all collectively missing.

Paolo