linux-kernel - Re: [PATCH 2/2] KVM: VMX: Add knob to allow rejecting kvm

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Date:   Wed, 25 May 2022 14:17:12 -0700
From:   Jim Mattson <jmattson@...gle.com>
To:     Sean Christopherson <seanjc@...gle.com>
Cc:     Paolo Bonzini <pbonzini@...hat.com>,
        Vitaly Kuznetsov <vkuznets@...hat.com>,
        Wanpeng Li <wanpengli@...cent.com>,
        Joerg Roedel <joro@...tes.org>, kvm@...r.kernel.org,
        linux-kernel@...r.kernel.org,
        Chenyi Qiang <chenyi.qiang@...el.com>,
        Lei Wang <lei4.wang@...el.com>
Subject: Re: [PATCH 2/2] KVM: VMX: Add knob to allow rejecting kvm_intel on
 inconsistent VMCS config

On Wed, May 25, 2022 at 2:04 PM Sean Christopherson <seanjc@...gle.com> wrote:
>
> Add an off-by-default module param, reject_inconsistent_vmcs_config, to
> allow rejecting the load of kvm_intel if an inconsistent VMCS config is
> detected.  Continuing on with an inconsistent, degraded config is
> undesirable when the CPU is expected to support a given set of features,
> e.g. can result in a misconfigured VM if userspace doesn't cross-check
> KVM_GET_SUPPORTED_CPUID, and/or can result in poor performance due to
> lack of fast MSR switching.
>
> Signed-off-by: Sean Christopherson <seanjc@...gle.com>
> ---
There are several inconsistent VMCS configs that are not rejected here
(e.g. "enable XSAVES/XRSTORS" on a CPU that doesn't support XSAVES).
Do you plan to include more checks in the future, or should this be,
"reject_some_inconsistent_vmcs_configs"? :-)