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Subject: Re: [PATCH 03/22] kvm: mmu: Init / Uninit the TDP MMU
To:     Sean Christopherson <sean.j.christopherson@intel.com>,
        Ben Gardon <bgardon@google.com>
Cc:     linux-kernel@vger.kernel.org, kvm@vger.kernel.org,
        Cannon Matthews <cannonmatthews@google.com>,
        Peter Xu <peterx@redhat.com>, Peter Shier <pshier@google.com>,
        Peter Feiner <pfeiner@google.com>,
        Junaid Shahid <junaids@google.com>,
        Jim Mattson <jmattson@google.com>,
        Yulei Zhang <yulei.kernel@gmail.com>,
        Wanpeng Li <kernellwp@gmail.com>,
        Vitaly Kuznetsov <vkuznets@redhat.com>,
        Xiao Guangrong <xiaoguangrong.eric@gmail.com>
References: <20200925212302.3979661-1-bgardon@google.com>
 <20200925212302.3979661-4-bgardon@google.com>
 <20200930165734.GE32672@linux.intel.com>
From:   Paolo Bonzini <pbonzini@redhat.com>
Message-ID: <2633cc07-f106-25ba-0ab9-d4a422aca171@redhat.com>
Date:   Wed, 30 Sep 2020 19:39:38 +0200
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On 30/09/20 18:57, Sean Christopherson wrote:
>> +
>> +static bool __read_mostly tdp_mmu_enabled = true;
>> +module_param_named(tdp_mmu, tdp_mmu_enabled, bool, 0644);
> This param should not exist until the TDP MMU is fully functional, e.g. running
> KVM against "kvm: mmu: Support zapping SPTEs in the TDP MMU" immediately hits a
> BUG() in the rmap code.  I haven't wrapped my head around the entire series to
> grok whether it make sense to incrementally enable the TDP MMU, but my gut says
> that's probably non-sensical.

No, it doesn't.  Whether to add the module parameter is kind of
secondary, but I agree it shouldn't be true---not even at the end of
this series, since fast page fault for example is not implemented yet.

Paolo