linux-kernel - Re: [PATCH mm-unstable v1 3/5] kvm/arm64: add kvm_arch_test_clear

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Message-ID: <CAOUHufYLmu7oowXZ5YmVJqgx5dHWdz-1eaqPiVzUq3RAY4e_6A@mail.gmail.com>
Date:   Thu, 23 Feb 2023 02:18:24 -0700
From:   Yu Zhao <yuzhao@...gle.com>
To:     Marc Zyngier <maz@...nel.org>
Cc:     Will Deacon <will@...nel.org>, Jonathan Corbet <corbet@....net>,
        Michael Larabel <michael@...haellarabel.com>,
        kvmarm@...ts.linux.dev, kvm@...r.kernel.org,
        linux-arm-kernel@...ts.infradead.org, linux-kernel@...r.kernel.org,
        linux-mm@...ck.org, linuxppc-dev@...ts.ozlabs.org, x86@...nel.org,
        linux-mm@...gle.com, Andrew Morton <akpm@...ux-foundation.org>,
        Paolo Bonzini <pbonzini@...hat.com>
Subject: Re: [PATCH mm-unstable v1 3/5] kvm/arm64: add kvm_arch_test_clear_young()

On Thu, Feb 23, 2023 at 2:03 AM Marc Zyngier <maz@...nel.org> wrote:
>
> On Thu, 23 Feb 2023 03:58:47 +0000,
> Yu Zhao <yuzhao@...gle.com> wrote:
> >
> > On Fri, Feb 17, 2023 at 2:00 AM Marc Zyngier <maz@...nel.org> wrote:
> > >
> > > On Fri, 17 Feb 2023 04:21:28 +0000,
> > > Yu Zhao <yuzhao@...gle.com> wrote:
> > > >
> > > > On Thu, Feb 16, 2023 at 9:12 PM Yu Zhao <yuzhao@...gle.com> wrote:
> > > > >
> > > > > This patch adds kvm_arch_test_clear_young() for the vast majority of
> > > > > VMs that are not pKVM and run on hardware that sets the accessed bit
> > > > > in KVM page tables.
> > >
> > > I'm really interested in how you can back this statement. 90% of the
> > > HW I have access to is not FEAT_HWAFDB capable, either because it
> > > predates the feature or because the feature is too buggy to be useful.
> >
> > This is my expericen too -- most devices are pre v8.2.
>
> And yet you have no issue writing the above. Puzzling.

That's best to my knowledge. Mind enlightening me?

> > > Do you have numbers?
> >
> > Let's do a quick market survey by segment. The following only applies
> > to ARM CPUs:
> >
> > 1. Phones: none of the major Android phone vendors sell phones running
> > VMs; no other major Linux phone vendors.
>
> Maybe you should have a reality check and look at what your own
> employer is shipping.

Which model? I'll look it up and see how/how I missed it.

> > 2. Laptops: only a very limited number of Chromebooks run VMs, namely
> > ACRVM. No other major Linux laptop vendors.
>
> Again, your employer disagree.

What do you mean? Sorry, I'm a little surprised here... I do know *a
lot* about Chromebooks.

> > 3. Desktops: no major Linux desktop vendors.
>
> My desktop disagree (I send this from my arm64 desktop VM ).

A model number please?

> > 4. Embedded/IoT/Router: no major Linux vendors run VMs (Android Auto
> > can be a VM guest on QNX host).
>
> This email is brought to you via a router VM on an arm64 box.

More details?

> > 5. Cloud: this is where the vast majority VMs come from. Among the
> > vendors available to the general public, Ampere is the biggest player.
> > Here [1] is a list of its customers. The A-bit works well even on its
> > EVT products (Neoverse cores).
>
> Just the phone stuff dwarfs the number of cloud hosts.

Please point me to something that I can work on so that I wouldn't
sound so ignorant next time.