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

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Date:   Mon, 19 Aug 2019 22:06:41 +0800
From:   Yang Weijiang <weijiang.yang@...el.com>
To:     Vitaly Kuznetsov <vkuznets@...hat.com>
Cc:     Yang Weijiang <weijiang.yang@...el.com>, 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

On Thu, Aug 15, 2019 at 04:03:31PM +0200, Vitaly Kuznetsov wrote:
> 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
OK, I'll follow your suggestion to add the exclusion, thanks!