From: Haibo Xu <haibo.xu@linaro.org>
To: Steven Price <steven.price@arm.com>
Cc: Marc Zyngier <maz@kernel.org>, Andrew Jones <drjones@redhat.com>,
Catalin Marinas <catalin.marinas@arm.com>,
Juan Quintela <quintela@redhat.com>,
Richard Henderson <richard.henderson@linaro.org>,
QEMU Developers <qemu-devel@nongnu.org>,
"Dr. David Alan Gilbert" <dgilbert@redhat.com>,
arm-mail-list <linux-arm-kernel@lists.infradead.org>,
kvmarm <kvmarm@lists.cs.columbia.edu>,
Thomas Gleixner <tglx@linutronix.de>,
Will Deacon <will@kernel.org>, Dave Martin <Dave.Martin@arm.com>,
lkml - Kernel Mailing List <linux-kernel@vger.kernel.org>
Subject: Re: [PATCH v5 0/2] MTE support for KVM guest
Date: Tue, 8 Dec 2020 17:51:24 +0800 [thread overview]
Message-ID: <CAJc+Z1FRJR5LHw-xZvPpeYF6+v+ZOcLt99X41xOMAbFmB2DJ2A@mail.gmail.com> (raw)
In-Reply-To: <46fd98a2-ee39-0086-9159-b38c406935ab@arm.com>
On Mon, 7 Dec 2020 at 22:48, Steven Price <steven.price@arm.com> wrote:
>
> On 04/12/2020 08:25, Haibo Xu wrote:
> > On Fri, 20 Nov 2020 at 17:51, Steven Price <steven.price@arm.com> wrote:
> >>
> >> On 19/11/2020 19:11, Marc Zyngier wrote:
> >>> On 2020-11-19 18:42, Andrew Jones wrote:
> >>>> On Thu, Nov 19, 2020 at 03:45:40PM +0000, Peter Maydell wrote:
> >>>>> On Thu, 19 Nov 2020 at 15:39, Steven Price <steven.price@arm.com> wrote:
> >>>>>> This series adds support for Arm's Memory Tagging Extension (MTE) to
> >>>>>> KVM, allowing KVM guests to make use of it. This builds on the
> >>>>> existing
> >>>>>> user space support already in v5.10-rc1, see [1] for an overview.
> >>>>>
> >>>>>> The change to require the VMM to map all guest memory PROT_MTE is
> >>>>>> significant as it means that the VMM has to deal with the MTE tags
> >>>>> even
> >>>>>> if it doesn't care about them (e.g. for virtual devices or if the VMM
> >>>>>> doesn't support migration). Also unfortunately because the VMM can
> >>>>>> change the memory layout at any time the check for PROT_MTE/VM_MTE has
> >>>>>> to be done very late (at the point of faulting pages into stage 2).
> >>>>>
> >>>>> I'm a bit dubious about requring the VMM to map the guest memory
> >>>>> PROT_MTE unless somebody's done at least a sketch of the design
> >>>>> for how this would work on the QEMU side. Currently QEMU just
> >>>>> assumes the guest memory is guest memory and it can access it
> >>>>> without special precautions...
> >>>>>
> >>>>
> >>>> There are two statements being made here:
> >>>>
> >>>> 1) Requiring the use of PROT_MTE when mapping guest memory may not fit
> >>>> QEMU well.
> >>>>
> >>>> 2) New KVM features should be accompanied with supporting QEMU code in
> >>>> order to prove that the APIs make sense.
> >>>>
> >>>> I strongly agree with (2). While kvmtool supports some quick testing, it
> >>>> doesn't support migration. We must test all new features with a migration
> >>>> supporting VMM.
> >>>>
> >>>> I'm not sure about (1). I don't feel like it should be a major problem,
> >>>> but (2).
> >>
> >> (1) seems to be contentious whichever way we go. Either PROT_MTE isn't
> >> required in which case it's easy to accidentally screw up migration, or
> >> it is required in which case it's difficult to handle normal guest
> >> memory from the VMM. I get the impression that probably I should go back
> >> to the previous approach - sorry for the distraction with this change.
> >>
> >> (2) isn't something I'm trying to skip, but I'm limited in what I can do
> >> myself so would appreciate help here. Haibo is looking into this.
> >>
> >
> > Hi Steven,
> >
> > Sorry for the later reply!
> >
> > I have finished the POC for the MTE migration support with the assumption
> > that all the memory is mapped with PROT_MTE. But I got stuck in the test
> > with a FVP setup. Previously, I successfully compiled a test case to verify
> > the basic function of MTE in a guest. But these days, the re-compiled test
> > can't be executed by the guest(very weird). The short plan to verify
> > the migration
> > is to set the MTE tags on one page in the guest, and try to dump the migrated
> > memory contents.
>
> Hi Haibo,
>
> 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.
>
> > I will update the status later next week!
>
> Great, I look forward to hearing how it goes.
>
> Thanks,
>
> Steve
next prev parent reply other threads:[~2020-12-08 9:52 UTC|newest]
Thread overview: 38+ messages / expand[flat|nested] mbox.gz Atom feed top
2020-11-19 15:38 [PATCH v5 0/2] MTE support for KVM guest Steven Price
2020-11-19 15:39 ` [PATCH v5 1/2] arm64: kvm: Save/restore MTE registers Steven Price
2020-11-19 15:39 ` [PATCH v5 2/2] arm64: kvm: Introduce MTE VCPU feature Steven Price
2020-11-19 15:45 ` [PATCH v5 0/2] MTE support for KVM guest Peter Maydell
2020-11-19 15:57 ` Steven Price
2020-11-19 16:39 ` Peter Maydell
2020-11-19 18:42 ` Andrew Jones
2020-11-19 19:11 ` Marc Zyngier
2020-11-20 9:50 ` Steven Price
2020-11-20 9:56 ` Marc Zyngier
2020-11-20 9:58 ` Steven Price
2020-12-04 8:25 ` Haibo Xu
2020-12-07 14:48 ` Steven Price
2020-12-07 15:27 ` Peter Maydell
2020-12-07 15:45 ` Steven Price
2020-12-07 16:05 ` Marc Zyngier
2020-12-07 16:34 ` Catalin Marinas
2020-12-07 19:03 ` Marc Zyngier
2020-12-08 17:21 ` Catalin Marinas
2020-12-08 18:21 ` Marc Zyngier
2020-12-09 12:44 ` Catalin Marinas
2020-12-09 13:25 ` Marc Zyngier
2020-12-09 15:27 ` Catalin Marinas
2020-12-09 18:27 ` Richard Henderson
2020-12-09 18:39 ` Catalin Marinas
2020-12-09 20:13 ` Richard Henderson
2020-12-09 20:20 ` Peter Maydell
2020-12-07 16:44 ` Dr. David Alan Gilbert
2020-12-07 17:10 ` Peter Maydell
2020-12-07 17:44 ` Dr. David Alan Gilbert
2020-12-08 10:05 ` Haibo Xu
2020-12-08 9:51 ` Haibo Xu [this message]
2020-12-08 10:01 ` Marc Zyngier
2020-12-08 10:10 ` Haibo Xu
2020-12-16 7:31 ` Haibo Xu
2020-12-16 10:22 ` Steven Price
2020-12-17 1:47 ` Haibo Xu
2020-11-23 12:16 ` Dr. David Alan Gilbert
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