From: Marc Zyngier <maz@kernel.org>
To: Paolo Bonzini <pbonzini@redhat.com>
Cc: Wanpeng Li <kernellwp@gmail.com>,
linux-kernel@vger.kernel.org, kvm@vger.kernel.org,
Ben Gardon <bgardon@google.com>,
Shakeel Butt <shakeelb@google.com>
Subject: Re: [PATCH] KVM: arm: memcg awareness
Date: Wed, 17 Mar 2021 11:03:14 +0000 [thread overview]
Message-ID: <87h7lahwjx.wl-maz@kernel.org> (raw)
In-Reply-To: <21d1f531-fe95-224d-0dac-6917d473063d@redhat.com>
On Wed, 17 Mar 2021 10:55:00 +0000,
Paolo Bonzini <pbonzini@redhat.com> wrote:
>
> On 17/03/21 11:53, Marc Zyngier wrote:
> > On Wed, 17 Mar 2021 10:40:23 +0000,
> > Paolo Bonzini <pbonzini@redhat.com> wrote:
> >>
> >> On 17/03/21 10:10, Marc Zyngier wrote:
> >>>> @@ -366,7 +366,7 @@ static int hyp_map_walker(u64 addr, u64 end, u32 level, kvm_pte_t *ptep,
> >>>> if (WARN_ON(level == KVM_PGTABLE_MAX_LEVELS - 1))
> >>>> return -EINVAL;
> >>>> - childp = (kvm_pte_t *)get_zeroed_page(GFP_KERNEL);
> >>>> + childp = (kvm_pte_t *)get_zeroed_page(GFP_KERNEL_ACCOUNT);
> >>> No, this is wrong.
> >>>
> >>> You cannot account the hypervisor page tables to the guest because we
> >>> don't ever unmap them, and that we can't distinguish two data
> >>> structures from two different VMs occupying the same page.
> >>
> >> If you never unmap them, there should at least be a shrinker to get
> >> rid of unused pages in the event of memory pressure.
> >
> > We don't track where these pages are coming from or whether they can
> > safely be unmapped. Until we can track such ownership and deal with
> > page sharing, these mappings have to stay,
> >
> > At most, this represent the amount of memory required to map the whole
> > of the linear mapping.
>
> Ah, these are the EL2 pages, not the stage2 page tables, right? If
> so, sorry for the noise.
Yes, EL2 page tables when running non-VHE. VHE doesn't have that
problem for obvious reasons. Stage-2 page tables can be completely
discarded at any point, and the MMU notifiers already deal with that.
M.
--
Without deviation from the norm, progress is not possible.
prev parent reply other threads:[~2021-03-17 11:04 UTC|newest]
Thread overview: 11+ messages / expand[flat|nested] mbox.gz Atom feed top
2021-03-17 5:46 [PATCH] KVM: arm: memcg awareness Wanpeng Li
2021-03-17 7:57 ` Michal Hocko
2021-03-17 8:04 ` Wanpeng Li
2021-03-17 8:04 ` Wanpeng Li
2021-03-17 9:44 ` Michal Hocko
2021-03-17 9:15 ` Marc Zyngier
2021-03-17 9:10 ` Marc Zyngier
2021-03-17 10:40 ` Paolo Bonzini
2021-03-17 10:53 ` Marc Zyngier
2021-03-17 10:55 ` Paolo Bonzini
2021-03-17 11:03 ` Marc Zyngier [this message]
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