linux-kernel - Re: [PATCH v7 3/4] KVM: x86/mmu: count KVM mmu usage in secondary pagetable stats.

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Date:   Tue, 30 Aug 2022 21:52:33 +0000
From:   Sean Christopherson <seanjc@...gle.com>
To:     Yosry Ahmed <yosryahmed@...gle.com>
Cc:     Tejun Heo <tj@...nel.org>, Johannes Weiner <hannes@...xchg.org>,
        Zefan Li <lizefan.x@...edance.com>,
        Marc Zyngier <maz@...nel.org>,
        James Morse <james.morse@....com>,
        Alexandru Elisei <alexandru.elisei@....com>,
        Suzuki K Poulose <suzuki.poulose@....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>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Michal Hocko <mhocko@...nel.org>,
        Roman Gushchin <roman.gushchin@...ux.dev>,
        Shakeel Butt <shakeelb@...gle.com>,
        Oliver Upton <oupton@...gle.com>, Huang@...gle.com,
        Shaoqin <shaoqin.huang@...el.com>, cgroups@...r.kernel.org,
        linux-kernel@...r.kernel.org, linux-arm-kernel@...ts.infradead.org,
        kvmarm@...ts.cs.columbia.edu, kvm@...r.kernel.org,
        linux-mm@...ck.org
Subject: Re: [PATCH v7 3/4] KVM: x86/mmu: count KVM mmu usage in secondary
 pagetable stats.

On Fri, Aug 26, 2022, Sean Christopherson wrote:
> On Tue, Aug 23, 2022, Yosry Ahmed wrote:
> > Count the pages used by KVM mmu on x86 in memory stats under secondary
> > pagetable stats (e.g. "SecPageTables" in /proc/meminfo) to give better
> > visibility into the memory consumption of KVM mmu in a similar way to
> > how normal user page tables are accounted.
> > 
> > Signed-off-by: Yosry Ahmed <yosryahmed@...gle.com>
> > Reviewed-by: Sean Christopherson <seanjc@...gle.com>
> > ---
> >  arch/x86/kvm/mmu/mmu.c     | 16 ++++++++++++++--
> >  arch/x86/kvm/mmu/tdp_mmu.c | 12 ++++++++++++
> >  2 files changed, 26 insertions(+), 2 deletions(-)
> > 
> > diff --git a/arch/x86/kvm/mmu/mmu.c b/arch/x86/kvm/mmu/mmu.c
> > index e418ef3ecfcb..4d38e4eba772 100644
> > --- a/arch/x86/kvm/mmu/mmu.c
> > +++ b/arch/x86/kvm/mmu/mmu.c
> > @@ -1665,6 +1665,18 @@ static inline void kvm_mod_used_mmu_pages(struct kvm *kvm, long nr)
> >  	percpu_counter_add(&kvm_total_used_mmu_pages, nr);
> >  }
> >  
> > +static void kvm_account_mmu_page(struct kvm *kvm, struct kvm_mmu_page *sp)
> > +{
> > +	kvm_mod_used_mmu_pages(kvm, +1);
> > +	kvm_account_pgtable_pages((void *)sp->spt, +1);
> > +}
> > +
> > +static void kvm_unaccount_mmu_page(struct kvm *kvm, struct kvm_mmu_page *sp)
> > +{
> > +	kvm_mod_used_mmu_pages(kvm, -1);
> > +	kvm_account_pgtable_pages((void *)sp->spt, -1);
> > +}
> 
> Hrm, this is causing build on x86 issues for me.  AFAICT, modpost doesn't detect
> that this creates a new module dependency on __mod_lruvec_page_state() and so doesn't
> refresh vmlinux.symvers.
> 
>   ERROR: modpost: "__mod_lruvec_page_state" [arch/x86/kvm/kvm.ko] undefined!
>   make[2]: *** [scripts/Makefile.modpost:128: modules-only.symvers] Error 1
>   make[1]: *** [Makefile:1769: modules] Error 2
>   make[1]: *** Waiting for unfinished jobs....
>   Kernel: arch/x86/boot/bzImage is ready  (#128)
>   make[1]: Leaving directory '/usr/local/google/home/seanjc/build/kernel/vm'
>   make: *** [Makefile:222: __sub-make] Error 2
> 
> Both gcc and clang yield the same behavior, so I doubt it's the compiler doing
> something odd.  Cleaning the build makes the problem go away, but that's a poor
> band-aid.
> 
> If I squash this with the prior patch that adds kvm_account_pgtable_pages() to
> kvm_host.h, modpost detects the need to refresh and all is well.
> 
> Given that ARM doesn't support building KVM as a module, i.e. can't run afoul
> of whatever modpost weirdness I'm hitting, I'm inclined to squash this with the
> previous patch and punt on the modpost issue so that we can get this merged.
> 
> Any objections?  Or thoughts on what's going wrong?

Pushed the series with the squash to branch `for_paolo/6.1` at:

    https://github.com/sean-jc/linux.git

Unless you hear otherwise, it will make its way to kvm/queue "soon".

Please yell if there are objections.