linux-kernel - Re: [PATCH 15/22] kvm: mmu: Support changed pte notifier in tdp MMU

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Message-ID: <CANgfPd_F_EurkfGquC79cEHa=4A2AMfnCAfMHPpAXa-6w4+bsg@mail.gmail.com>
Date:   Wed, 7 Oct 2020 10:30:10 -0700
From:   Ben Gardon <bgardon@...gle.com>
To:     Paolo Bonzini <pbonzini@...hat.com>
Cc:     LKML <linux-kernel@...r.kernel.org>, kvm <kvm@...r.kernel.org>,
        Cannon Matthews <cannonmatthews@...gle.com>,
        Peter Xu <peterx@...hat.com>,
        Sean Christopherson <sean.j.christopherson@...el.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 15/22] kvm: mmu: Support changed pte notifier in tdp MMU

On Wed, Oct 7, 2020 at 10:18 AM Paolo Bonzini <pbonzini@...hat.com> wrote:
>
> On 07/10/20 18:53, Ben Gardon wrote:
> >> in addition to the previously-mentioned cleanup of always calling
> >> handle_changed_spte instead of special-casing calls to two of the
> >> three functions.  It would be a nice place to add the
> >> trace_kvm_mmu_set_spte tracepoint, too.
> > I'm not sure we can avoid special casing calls to the access tracking
> > and dirty logging handler functions. At least in the past that's
> > created bugs with things being marked dirty or accessed when they
> > shouldn't be. I'll revisit those assumptions. It would certainly be
> > nice to get rid of that complexity.
> >
> > I agree that putting the SPTE assignment and handler functions in a
> > helper function would clean up the code. I'll do that.
>
> Well that's not easy if you have to think of which functions have to be
> called.
>
> I'll take a closer look at the access tracking and dirty logging cases
> to try and understand what those bugs can be.  Apart from that I have my
> suggested changes and I can probably finish testing them and send them
> out tomorrow.

Awesome, thank you. I'll look forward to seeing them. Will you be
applying those changes to the tdp_mmu branch you created as well?

>
> Paolo
>
> > I got some
> > feedback on the RFC I sent last year which led me to open-code a lot
> > more, but I think this is still a good cleanup.
>