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

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Message-ID: <7636707a-b622-90a3-e641-18662938f6dd@redhat.com>
Date:   Wed, 7 Oct 2020 19:18:16 +0200
From:   Paolo Bonzini <pbonzini@...hat.com>
To:     Ben Gardon <bgardon@...gle.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 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.

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.