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

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Message-ID: <622ffc59-d914-c718-3f2f-952f714ac63c@redhat.com>
Date:   Mon, 28 Sep 2020 17:11:24 +0200
From:   Paolo Bonzini <pbonzini@...hat.com>
To:     Ben Gardon <bgardon@...gle.com>, linux-kernel@...r.kernel.org,
        kvm@...r.kernel.org
Cc:     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 25/09/20 23:22, Ben Gardon wrote:
> +		*iter.sptep = 0;
> +		handle_changed_spte(kvm, as_id, iter.gfn, iter.old_spte,
> +				    new_spte, iter.level);
> +

Can you explain why new_spte is passed here instead of 0?

All calls to handle_changed_spte are preceded by "*something = 
new_spte" except this one, so I'm thinking of having a change_spte 
function like

static void change_spte(struct kvm *kvm, int as_id, gfn_t gfn,
                        u64 *sptep, u64 new_spte, int level)
{
        u64 old_spte = *sptep;
        *sptep = new_spte;

        __handle_changed_spte(kvm, as_id, gfn, old_spte, new_spte, level);
        handle_changed_spte_acc_track(old_spte, new_spte, level);
        handle_changed_spte_dirty_log(kvm, as_id, gfn, old_spte, new_spte, level);
}

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.

Paolo