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

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Date:   Wed, 17 Feb 2021 19:00:52 +0100
From:   Paolo Bonzini <pbonzini@...hat.com>
To:     Sean Christopherson <seanjc@...gle.com>
Cc:     Maxim Levitsky <mlevitsk@...hat.com>, 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 18:57, Sean Christopherson wrote:
>> That said, I'm also rusty on_why_  this code is needed.  Why isn't it enough
>> to inject the exception normally, and let nested_vmx_check_exception decide
>> whether to inject a vmexit to L1 or an exception into L2?
>
> Hmm, I suspect it was required at one point due to deficiencies elsewhere.
> Handling this in the common fault handler logic does seem like the right
> approach.

I think I'm going to merge a variant of patch 5 just to unbreak things. 
But we should get rid of all this because after the exception payload 
changes we shouldn't need it.

Paolo

>> Also, bonus question which should have been in the 5/7 changelog: are there
>> kvm-unit-tests testcases that fail with npt=0, and if not could we write
>> one?  [Answer: the mode_switch testcase fails, but I haven't checked why].