Re: [PATCH 2/4] iommu/arm-smmu-v3: Document MMU-700 erratum 2812531

Re: [PATCH 2/4] iommu/arm-smmu-v3: Document MMU-700 erratum 2812531

[Nicolin Chen]

On Fri, May 12, 2023 at 08:23:54PM +0100, Robin Murphy wrote:
 
> On 2023-05-10 19:31, Nicolin Chen wrote:
> > On Wed, May 10, 2023 at 11:12:05AM -0700, Nicolin Chen wrote:
> > > On Wed, May 10, 2023 at 04:38:44PM +0100, Robin Murphy wrote:
> > > 
> > > > To work around MMU-700 erratum 2812531 we need to ensure that certain
> > > > sequences of commands cannot be issued without an intervening sync. In
> > > > practice this falls out of our current command-batching machinery
> > > > anyway - each batch only contains a single type of invalidation command,
> > > 
> > > Hmm. This doesn't apply to the user cache invalidation solution
> > > in my v2. A user cmdq could possibly mix different commands in
> > > a single batch if the driver isn't aware of such an errata. So,
> > > I think I'd need some twist when the host has a FORCE_SYNC flag
> > > in my v3.
> > 
> > Just found that you unset the NESTING feature flag in PATCH-4
> > for this errata too. So, the solution in my v2 should be safe.
> 
> For the short term at least - we will still need to come up with a more
> practical active mitigation sooner rather than later, since I imagine
> people are likely to be a bit miffed if nesting support lands in distros
> but still refuses to play at all on the newest shiniest hardware.
> Unfortunately all current versions of MMU-700 are affected (hence the
> unconditional nature of this patch), and some of those are going to
> found in production SoCs.

Okay. I will try adding a WAR function following the doc:

1. A Stage 1 Invalidation that is followed by a Stage 2 invalidation
2. A Configuration Invalidation that is followed by any TLB Invalidation
3. A Leaf invalidation that is followed by a Non-leaf invalidation

We don't need anything for (1) as a user CMDQ only has stage-1
invalidations. Adding a SYNC after every CFIG_CD(_ALL) should
work for (2). Then for (3), need to check the leaf bit between
two adjacent NH_VA/NH_VAA commands.

Thanks
Nic

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Re: [PATCH 1/4] iommu/arm-smmu-v3: Work around MMU-600 erratum 1076982

[Nicolin Chen]

On Wed, May 10, 2023 at 10:40:42AM -0700, Nicolin Chen wrote:
> On Wed, May 10, 2023 at 04:38:43PM +0100, Robin Murphy wrote:
> 
> > MMU-600 versions prior to r1p0 fail to correctly generate a WFE wakeup
> > event when the command queue transitions fom full to non-full. We can
> > easily work around this by simply hiding the SEV capability such that we
> > fall back to polling for space in the queue - since MMU-600 implements
> > MSIs we wouldn't expect to need SEV for sync completion either, so this
> > should have little to no impact.
> > 
> > Signed-off-by: Robin Murphy <robin.murphy@arm.com>
> 
> Reviewed-by: Nicolin Chen <nicolinc@nvidia.com>

It happens that I have a simulation environment where the
IIDR value hits the errata, i.e. the NESTING feature bit
gets canceled by this patch. So,

Tested-by: Nicolin Chen <nicolinc@nvidia.com>

Hopefully we can get this series merged soon.

Thanks!
Nic

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Re: [PATCH 0/4] iommu/arm-smmu-v3: Arm SMMU errata bits

[Will Deacon]

On Wed, 10 May 2023 16:38:42 +0100, Robin Murphy wrote:
> Further to the discussion on the nesting series a while back, here's a
> mini-series to help us start taking more of an interest in SMMU errata.
> Patch #1 is more about the infrastucture than that erratum itself, but
> since I *had* already written it up (5 years ago!) I figured why not
> just build on it as-is. The rest is effectively just documentation at
> this point, but getting us ready for all the hitherto unmet conditions
> that IOMMUFD nesting is going to open up.
> 
> [...]

Applied to will (for-joerg/arm-smmu/updates), thanks!

[1/4] iommu/arm-smmu-v3: Work around MMU-600 erratum 1076982
      https://git.kernel.org/will/c/f322e8af35c7
[2/4] iommu/arm-smmu-v3: Document MMU-700 erratum 2812531
      https://git.kernel.org/will/c/309a15cb16bb
[3/4] iommu/arm-smmu-v3: Add explicit feature for nesting
      https://git.kernel.org/will/c/1d9777b9f3d5
[4/4] iommu/arm-smmu-v3: Document nesting-related errata
      https://git.kernel.org/will/c/0bfbfc526c70

Cheers,
-- 
Will

https://fixes.arm64.dev
https://next.arm64.dev
https://will.arm64.dev

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