linux-kernel - Re: [PATCH v5 0/2] MTE support for KVM guest

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Message-ID: <CAJc+Z1EafkLezXv=+1aPbaXo9uWpcB77iM32M70oyP6zEzacjw@mail.gmail.com>
Date:   Tue, 8 Dec 2020 18:10:51 +0800
From:   Haibo Xu <haibo.xu@...aro.org>
To:     Marc Zyngier <maz@...nel.org>
Cc:     Steven Price <steven.price@....com>,
        Andrew Jones <drjones@...hat.com>,
        Catalin Marinas <catalin.marinas@....com>,
        Juan Quintela <quintela@...hat.com>,
        Richard Henderson <richard.henderson@...aro.org>,
        QEMU Developers <qemu-devel@...gnu.org>,
        "Dr. David Alan Gilbert" <dgilbert@...hat.com>,
        arm-mail-list <linux-arm-kernel@...ts.infradead.org>,
        kvmarm <kvmarm@...ts.cs.columbia.edu>,
        Thomas Gleixner <tglx@...utronix.de>,
        Will Deacon <will@...nel.org>,
        Dave Martin <Dave.Martin@....com>,
        lkml - Kernel Mailing List <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH v5 0/2] MTE support for KVM guest

On Tue, 8 Dec 2020 at 18:01, Marc Zyngier <maz@...nel.org> wrote:
>
> On 2020-12-08 09:51, Haibo Xu wrote:
> > On Mon, 7 Dec 2020 at 22:48, Steven Price <steven.price@....com> wrote:
> >>
>
> [...]
>
> >> Sounds like you are making good progress - thanks for the update. Have
> >> you thought about how the PROT_MTE mappings might work if QEMU itself
> >> were to use MTE? My worry is that we end up with MTE in a guest
> >> preventing QEMU from using MTE itself (because of the PROT_MTE
> >> mappings). I'm hoping QEMU can wrap its use of guest memory in a
> >> sequence which disables tag checking (something similar will be needed
> >> for the "protected VM" use case anyway), but this isn't something I've
> >> looked into.
> >
> > As far as I can see, to map all the guest memory with PROT_MTE in VMM
> > is a little weird, and lots of APIs have to be changed to include this
> > flag.
> > IMHO, it would be better if the KVM can provide new APIs to load/store
> > the
> > guest memory tag which may make it easier to enable the Qemu migration
> > support.
>
> On what granularity? To what storage? How do you plan to synchronise
> this
> with the dirty-log interface?

The Qemu would migrate page by page, and if one page has been migrated but
becomes dirty again, the migration process would re-send this dirty page.
The current MTE migration POC codes would try to send the page tags just after
the page data, if one page becomes dirty again, the page data and the tags would
be re-sent.

>
> Thanks,
>
>          M.
> --
> Jazz is not dead. It just smells funny...