linux-kernel - Re: [PATCH 03/22] kvm: mmu: Init / Uninit the TDP MMU

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Date:   Wed, 30 Sep 2020 11:42:42 -0700
From:   Ben Gardon <bgardon@...gle.com>
To:     Paolo Bonzini <pbonzini@...hat.com>
Cc:     Sean Christopherson <sean.j.christopherson@...el.com>,
        LKML <linux-kernel@...r.kernel.org>, kvm <kvm@...r.kernel.org>,
        Cannon Matthews <cannonmatthews@...gle.com>,
        Peter Xu <peterx@...hat.com>, Peter Shier <pshier@...gle.com>,
        Peter Feiner <pfeiner@...gle.com>,
        Junaid Shahid <junaids@...gle.com>,
        Jim Mattson <jmattson@...gle.com>,
        Yulei Zhang <yulei.kernel@...il.com>,
        Wanpeng Li <kernellwp@...il.com>,
        Vitaly Kuznetsov <vkuznets@...hat.com>,
        Xiao Guangrong <xiaoguangrong.eric@...il.com>
Subject: Re: [PATCH 03/22] kvm: mmu: Init / Uninit the TDP MMU

On Wed, Sep 30, 2020 at 10:39 AM Paolo Bonzini <pbonzini@...hat.com> wrote:
>
> 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
>
I fully agree, sorry about that. I should have at least defaulted the
module parameter to false before sending the series out. I'll remedy
that in the next patch set. (Unless you beat me to it, Paolo)