linux-kernel - Re: [PATCH RESEND v4 5/9] KVM: VMX: Add init/set/get functions for SPP

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Message-ID: <87o90q8r0s.fsf@vitty.brq.redhat.com>
Date:   Thu, 15 Aug 2019 16:03:31 +0200
From:   Vitaly Kuznetsov <vkuznets@...hat.com>
To:     Yang Weijiang <weijiang.yang@...el.com>
Cc:     kvm@...r.kernel.org, linux-kernel@...r.kernel.org, mst@...hat.com,
        rkrcmar@...hat.com, jmattson@...gle.com, yu.c.zhang@...el.com,
        alazar@...defender.com, pbonzini@...hat.com,
        sean.j.christopherson@...el.com
Subject: Re: [PATCH RESEND v4 5/9] KVM: VMX: Add init/set/get functions for SPP

Yang Weijiang <weijiang.yang@...el.com> writes:

> After looked into the issue and others, I feel to make SPP co-existing
> with nested VM is not good, the major reason is, L1 pages protected by
> SPP are transparent to L1 VM, if it launches L2 VM, probably the
> pages would be allocated to L2 VM, and that will bother to L1 and L2.
> Given the feature is new and I don't see nested VM can benefit
> from it right now, I would like to make SPP and nested feature mutually
> exclusive, i.e., detecting if the other part is active before activate one
> feature,what do you think of it? 

I was mostly worried about creating a loophole (if I understand
correctly) for guests to defeat SPP protection: just launching a nested
guest and giving it a protected page. I don't see a problem if we limit
SPP to non-nested guests as step 1: we, however, need to document this
side-effect of the ioctl. Also, if you decide to do this enforecement,
I'd suggest you forbid VMLAUCH/VMRESUME and not VMXON as kvm module
loads in linux guests automatically when the hardware is suitable.

Thanks,

-- 
Vitaly