linux-kernel - Re: [PATCH v3 1/6] KVM: x86/mmu: Set lpage_disallowed in TDP MMU before setting SPTE

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Date:   Mon, 4 Apr 2022 11:54:23 -0700
From:   Ben Gardon <bgardon@...gle.com>
To:     Sean Christopherson <seanjc@...gle.com>
Cc:     Mingwei Zhang <mizhang@...gle.com>,
        Paolo Bonzini <pbonzini@...hat.com>,
        Vitaly Kuznetsov <vkuznets@...hat.com>,
        Wanpeng Li <wanpengli@...cent.com>,
        Jim Mattson <jmattson@...gle.com>,
        Joerg Roedel <joro@...tes.org>, kvm <kvm@...r.kernel.org>,
        LKML <linux-kernel@...r.kernel.org>,
        Yosry Ahmed <yosryahmed@...gle.com>,
        David Matlack <dmatlack@...gle.com>,
        Jing Zhang <jingzhangos@...gle.com>,
        Peter Xu <peterx@...hat.com>
Subject: Re: [PATCH v3 1/6] KVM: x86/mmu: Set lpage_disallowed in TDP MMU
 before setting SPTE

On Mon, Apr 4, 2022 at 11:20 AM Sean Christopherson <seanjc@...gle.com> wrote:
>
> On Mon, Apr 04, 2022, Ben Gardon wrote:
> > On Thu, Mar 31, 2022 at 11:36 PM Mingwei Zhang <mizhang@...gle.com> wrote:
> > > diff --git a/arch/x86/kvm/mmu/mmu_internal.h b/arch/x86/kvm/mmu/mmu_internal.h
> > > index 1bff453f7cbe..4a0087efa1e3 100644
> > > --- a/arch/x86/kvm/mmu/mmu_internal.h
> > > +++ b/arch/x86/kvm/mmu/mmu_internal.h
> > > @@ -168,7 +168,7 @@ void disallowed_hugepage_adjust(struct kvm_page_fault *fault, u64 spte, int cur_
> > >
> > >  void *mmu_memory_cache_alloc(struct kvm_mmu_memory_cache *mc);
> > >
> > > -void account_huge_nx_page(struct kvm *kvm, struct kvm_mmu_page *sp);
> > > +void __account_huge_nx_page(struct kvm *kvm, struct kvm_mmu_page *sp);
> >
> > I believe we need to modify the usage of this function in
> > paging_tmpl.h as well, at which point there should be no users of
> > account_huge_nx_page, so we can just modify the function directly
> > instead of adding a __helper.
> > (Disregard if the source I was looking at was out of date. Lots of
> > churn in this code recently.)
>
> paging_tmpl.h is shadow paging only, i.e. will always handled page faults with
> mmu_lock held for write and it also needs the check for sp->lpage_disallowed
> already being set.  Only the TDP MMU code is special in that (a) it holds mmu_lock
> for read and (b) never reuses shadow pages when inserting into the page tables.
>
> Or did I completely misunderstand what you meant by "need to modify the usage"?

Ah right duh. For some reason I thought we were modifying __direct_map
in this commit too. Nevermind, no change needed.