linux-kernel - Re: [PATCH v3 4/4] KVM: SVM: Support #GP handling for the case of nested on nested

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Message-ID: <f3611af9-dce2-b07f-e5c4-5a47c7e519a6@redhat.com>
Date:   Tue, 26 Jan 2021 12:39:16 +0100
From:   Paolo Bonzini <pbonzini@...hat.com>
To:     Wei Huang <wei.huang2@....com>, kvm@...r.kernel.org
Cc:     linux-kernel@...r.kernel.org, vkuznets@...hat.com,
        mlevitsk@...hat.com, seanjc@...gle.com, joro@...tes.org,
        bp@...en8.de, tglx@...utronix.de, mingo@...hat.com, x86@...nel.org,
        jmattson@...gle.com, wanpengli@...cent.com, bsd@...hat.com,
        dgilbert@...hat.com, luto@...capital.net
Subject: Re: [PATCH v3 4/4] KVM: SVM: Support #GP handling for the case of
 nested on nested

On 26/01/21 09:18, Wei Huang wrote:
> Under the case of nested on nested (L0->L1->L2->L3), #GP triggered by 
> SVM instructions can be hided from L1. Instead the hypervisor can inject 
> the proper #VMEXIT to inform L1 of what is happening. Thus L1 can avoid 
> invoking the #GP workaround. For this reason we turns on guest VM's 
> X86_FEATURE_SVME_ADDR_CHK bit for KVM running inside VM to receive the 
> notification and change behavior.

Slightly reworked commit message:

KVM: SVM: Fix #GP handling for doubly-nested virtualization

Under the case of nested on nested (L0, L1, L2 are all hypervisors),
#GP triggered by SVM instructions can be hidden from L1.  Because
we do not support emulation of the vVMLOAD/VMSAVE feature, the
L0 hypervisor can inject the proper #VMEXIT to inform L1 of what is
happening and L1 can avoid invoking the #GP workaround.

Thanks,

Paolo