[RFC PATCH v2 0/8] ACPI/IORT: Support for IORT RMR node

Fri Dec 18 05:53:19 EST 2020

On Thu, Dec 17, 2020 at 4:53 PM Jon Nettleton <jon at solid-run.com> wrote:
>
> On Thu, Dec 17, 2020 at 4:42 PM Shameerali Kolothum Thodi
> <shameerali.kolothum.thodi at huawei.com> wrote:
> >
> >
> >
> > > -----Original Message-----
> > > From: Jon Nettleton [mailto:jon at solid-run.com]
> > > Sent: 17 December 2020 14:48
> > > To: Shameerali Kolothum Thodi <shameerali.kolothum.thodi at huawei.com>
> > > Cc: Steven Price <steven.price at arm.com>; Robin Murphy
> > > <robin.murphy at arm.com>; linux-arm-kernel at lists.infradead.org;
> > > linux-acpi at vger.kernel.org; iommu at lists.linux-foundation.org;
> > > devel at acpica.org; lorenzo.pieralisi at arm.com; joro at 8bytes.org; Guohanjun
> > > (Hanjun Guo) <guohanjun at huawei.com>; Linuxarm <linuxarm at huawei.com>;
> > > Jonathan Cameron <jonathan.cameron at huawei.com>;
> > > Sami.Mujawar at arm.com; wanghuiqiang <wanghuiqiang at huawei.com>
> > > Subject: Re: [RFC PATCH v2 0/8] ACPI/IORT: Support for IORT RMR node
> > >
> > > On Mon, Dec 14, 2020 at 3:48 PM Shameerali Kolothum Thodi
> > > <shameerali.kolothum.thodi at huawei.com> wrote:
> > > >
> > > >
> > > >
> > > > > -----Original Message-----
> > > > > From: Steven Price [mailto:steven.price at arm.com]
> > > > > Sent: 14 December 2020 13:43
> > > > > To: Robin Murphy <robin.murphy at arm.com>; Shameerali Kolothum Thodi
> > > > > <shameerali.kolothum.thodi at huawei.com>;
> > > > > linux-arm-kernel at lists.infradead.org; linux-acpi at vger.kernel.org;
> > > > > iommu at lists.linux-foundation.org; devel at acpica.org
> > > > > Cc: Linuxarm <linuxarm at huawei.com>; lorenzo.pieralisi at arm.com;
> > > > > joro at 8bytes.org; wanghuiqiang <wanghuiqiang at huawei.com>; Guohanjun
> > > > > (Hanjun Guo) <guohanjun at huawei.com>; Jonathan Cameron
> > > > > <jonathan.cameron at huawei.com>; Sami.Mujawar at arm.com
> > > > > Subject: Re: [RFC PATCH v2 0/8] ACPI/IORT: Support for IORT RMR node
> > > > >
> > > > > On 14/12/2020 12:33, Robin Murphy wrote:
> > > > > > On 2020-12-14 10:55, Shameerali Kolothum Thodi wrote:
> > > > > >> Hi Steve,
> > > > > >>
> > > > > >>> -----Original Message-----
> > > > > >>> From: Steven Price [mailto:steven.price at arm.com]
> > > > > >>> Sent: 10 December 2020 10:26
> > > > > >>> To: Shameerali Kolothum Thodi
> > > > > <shameerali.kolothum.thodi at huawei.com>;
> > > > > >>> linux-arm-kernel at lists.infradead.org; linux-acpi at vger.kernel.org;
> > > > > >>> iommu at lists.linux-foundation.org; devel at acpica.org
> > > > > >>> Cc: Linuxarm <linuxarm at huawei.com>; lorenzo.pieralisi at arm.com;
> > > > > >>> joro at 8bytes.org; robin.murphy at arm.com; wanghuiqiang
> > > > > >>> <wanghuiqiang at huawei.com>; Guohanjun (Hanjun Guo)
> > > > > >>> <guohanjun at huawei.com>; Jonathan Cameron
> > > > > >>> <jonathan.cameron at huawei.com>; Sami.Mujawar at arm.com
> > > > > >>> Subject: Re: [RFC PATCH v2 0/8] ACPI/IORT: Support for IORT RMR node
> > > > > >>>
> > > > > >>> On 19/11/2020 12:11, Shameer Kolothum wrote:
> > > > > >>>> RFC v1 --> v2:
> > > > > >>>>    - Added a generic interface for IOMMU drivers to retrieve all the
> > > > > >>>>      RMR info associated with a given IOMMU.
> > > > > >>>>    - SMMUv3 driver gets the RMR list during probe() and installs
> > > > > >>>>      bypass STEs for all the SIDs in the RMR list. This is to keep
> > > > > >>>>      the ongoing traffic alive(if any) during SMMUv3 reset. This is
> > > > > >>>>      based on the suggestions received for v1 to take care of the
> > > > > >>>>      EFI framebuffer use case. Only sanity tested for now.
> > > > > >>>
> > > > > >>> Hi Shameer,
> > > > > >>>
> > > > > >>> Sorry for not looking at this before.
> > > > > >>>
> > > > > >>> Do you have any plans to implement support in the SMMUv2 driver?
> > > The
> > > > > >>> platform I've been testing the EFI framebuffer support on has the
> > > > > >>> display controller behind SMMUv2, so as it stands this series doesn't
> > > > > >>> work. I did hack something up for SMMUv2 so I was able to test the
> > > first
> > > > > >>> 4 patches.
> > > > > >>
> > > > > >> Thanks for taking a look. Sure, I can look into adding the support for
> > > > > >> SMMUv2.
> > > > >
> > > > > Great, thanks!
> > > > >
> > > > > >>>
> > > > > >>>>    - During the probe/attach device, SMMUv3 driver reserves any
> > > > > >>>>      RMR region associated with the device such that there is a
> > > unity
> > > > > >>>>      mapping for them in SMMU.
> > > > > >>>
> > > > > >>> For the EFI framebuffer use case there is no device to attach so I
> > > > > >>> believe we are left with just the stream ID in bypass mode - which is
> > > > > >>> definitely an improvement (the display works!)
> > > > > >>
> > > > > >> Cool. That’s good to know.
> > > > > >>
> > > > > >>   but not actually a unity
> > > > > >>> mapping of the RMR range. I'm not sure whether it's worth fixing this
> > > or
> > > > > >>> not, but I just wanted to point out there's still a need for a driver
> > > > > >>> for the device before the bypass mode is replaced with the unity
> > > > > >>> mapping.
> > > > > >>
> > > > > >> I am not sure either. My idea was we will have bypass STE setup for
> > > > > >> all devices
> > > > > >> with RMR initially and when the corresponding driver takes over(if
> > > > > >> that happens)
> > > > > >> we will have the unity mapping setup properly for the RMR regions. And
> > > > > >> for cases
> > > > > >> like the above, it will remain in the bypass mode.
> > > > > >>
> > > > > >> Do you see any problem(security?) if the dev streams remain in bypass
> > > > > >> mode for
> > > > > >> this dev? Or is it possible to have a stub driver for this dev, so
> > > > > >> that we will have
> > > > > >> the probe/attach invoked and everything will fall in place?
> > > > > >
> > > > > > The downside is that if a driver never binds to that device, it remains
> > > > > > bypassed. If some other externally-controlled malicious device could
> > > > > > manage to spoof that device's requester ID, that could potentially be
> > > > > > exploited.
> > > > > >
> > > > > >> TBH, I haven't looked into creating a temp domain for these types of
> > > > > >> the devices
> > > > > >> and also not sure how we benefit from that compared to the STE bypass
> > > > > >> mode.
> > > > > >
> > > > > > That said, setting up temporary translation contexts that ensure any
> > > > > > access can *only* be to RMR regions until a driver takes over is an
> > > > > > awful lot more work. I'm inclined to be pragmatic here and say we should
> > > > > > get things working at all with the simple bypass STE/S2CR method, then
> > > > > > look at adding the higher-security effort on top.
> > > > > >
> > > > > > Right now systems that need this are either broken (but effectively
> > > > > > secure) or using default bypass with SMMUv2. People who prefer to
> > > > > > maintain security over functionality in the interim can maintain that
> > > > > > status quo by simply continuing to not describe any RMRs.
> > > > >
> > > > > I agree with Robin, let's get this working with the bypass mode (until
> > > > > the device binds) like you've currently got. It's much better than what
> > > > > we have otherwise. Then once that is merged we can look at the temporary
> > > > > translation context or stub driver. The temporary translation context
> > > > > would be 'neatest', but I'm only aware of the EFI framebuffer use case
> > > > > and for that it might be possible to do something simpler - if indeed
> > > > > anything is needed at all. I'm not sure how much we need to be worried
> > > > > about malicious devices spoofing requester IDs.
> > > >
> > > > Perfect. I will keep the STE bypass and respin the series once the update
> > > > to the IORT rev E is made public(hope that will happen soon). In the
> > > > meantime, appreciate any feedback on the rest of the patches in this series.
> > >
> > > Shameer,
> >
> > Hi Jon,
> >
> > >
> > > I am pretty sure rev E is already public.  You can find it here.
> > >
> > > https://developer.arm.com/documentation/den0049/latest/
> > >
> > > It is also marked non-confidential.
> >
> > Yes, Rev E is already out there. But I am told that ARM folks are working on
> > some updates to the IORT spec, especially around the RMR topic. Hopefully
> > it will be out soon.
>
> Yes there are some changes coming to the SPEC but I don't know if it is
> worth holding up your patchset as an initial implementation.  If you would
> like I am more than happy to bring this up as a topic for the next Steering
> Committee meeting.
>
> Jon

Shameer,

My first attempt at smmuv2 support can be found in this kernel branch.

https://github.com/SolidRun/linux-stable/commits/linux-5.10.y-cex7

It is functioning if the bypass SMRs are setup in the firmware and RMR's
are exposed in the ACPI tables.  Different from your situation we do want
the device to reclaim the RMR's associated with it on initialization, and I
am still seeing issues there.  I need to spend more time figuring out why
this is not working properly.

-Jon

>
> >
> > >
> > > I also have initial patches for edk2 and the HoneyComb LX2160a
> > > ACPI tables adding RMR nodes that partially work with your patches.
> >
> > Thanks for the update and good to know that it is useful.
> >
> > Shameer
> >
> > > This is with basic SMMUv2 support but since you have more experience
> > > this this I am more than happy to work with you on your patchset.
> > >
> > > -Jon
> > >
> > >
> > > >
> > > > Thanks,
> > > > Shameer
> > > > _______________________________________________
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