linux-kernel - Re: [PATCH v7 4/4] KVM: arm64/mmu: count KVM s2 mmu usage in secondary pagetable stats

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Date:   Wed, 24 Aug 2022 14:43:43 +0100
From:   Ryan Roberts <ryan.roberts@....com>
To:     Yosry Ahmed <yosryahmed@...gle.com>, 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>,
        Sean Christopherson <seanjc@...gle.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>
Cc:     kvm@...r.kernel.org, linux-kernel@...r.kernel.org,
        Huang@...gle.com, Shaoqin <shaoqin.huang@...el.com>,
        linux-mm@...ck.org, cgroups@...r.kernel.org,
        kvmarm@...ts.cs.columbia.edu, linux-arm-kernel@...ts.infradead.org,
        nd@....com
Subject: Re: [PATCH v7 4/4] KVM: arm64/mmu: count KVM s2 mmu usage in
 secondary pagetable stats

> Count the pages used by KVM in arm64 for stage2 mmu 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: Oliver Upton <oliver.upton@...ux.dev>
> Reviewed-by: Marc Zyngier <maz@...nel.org>
> ---

I see that you are not including the memory reserved for the host stage2 
table when using protected KVM. Is this something worth adding? (See 
arch/arm64/kvm/pkvm.c:kvm_hyp_reserve()).

This reservation is done pretty early on in bootmem_init() so not sure 
if this could cause some init ordering issues that might be tricky to 
solve though.

Thanks,
Ryan