Re: [PATCH v2 1/1] iommu/arm-smmu-v3: Fix error case of range command

Will Deacon
2023-08-18T16:21:48Z

On Fri, Aug 18, 2023 at 05:19:31PM +0100, Robin Murphy wrote:
> On 2023-08-09 14:48, Robin Murphy wrote:
> [...]
> > Does the patch below work for you?
>
> Any comments on this? Just noticed this commit on a local dev branch and
> realised I'd totally forgotten about it already. I'm pretty confident it
> ought to be right, but then it *was* also me who missed the original bug to
> begin with... ;)

I'm happy to take it if zhurui can confirm that it fixes their issue...

Will (had also forgotten about this)

> > ----->8-----
> > Subject: [PATCH] iommu/arm-smmu-v3: Avoid constructing invalid range
> > commands
> >
> > Although io-pgtable's non-leaf invalidations are always for full tables,
> > I missed that SVA also uses non-leaf invalidations, while being at the
> > mercy of whatever range the MMU notifier throws at it. This means it
> > definitely wants the previous TTL fix as well, since it also doesn't
> > know exactly which leaf level(s) may need invalidating, but it can also
> > give us less-aligned ranges wherein certain corners may lead to building
> > an invalid command where TTL, Num and Scale are all 0. It should be fine
> > to handle this by over-invalidating an extra page, since falling back to
> > a non-range command opens up a whole can of errata-flavoured worms.
> >
> > Fixes: 6833b8f2e199 ("iommu/arm-smmu-v3: Set TTL invalidation hint better")
> > Reported-by: Rui Zhu <zhurui3@huawei.com>
> > Signed-off-by: Robin Murphy <robin.murphy@arm.com>
> > ---
> >  drivers/iommu/arm/arm-smmu-v3/arm-smmu-v3.c | 15 ++++++++++-----
> >  1 file changed, 10 insertions(+), 5 deletions(-)
> >
> > diff --git a/drivers/iommu/arm/arm-smmu-v3/arm-smmu-v3.c
> > b/drivers/iommu/arm/arm-smmu-v3/arm-smmu-v3.c
> > index 9b0dc3505601..6ccbae9b93a1 100644
> > --- a/drivers/iommu/arm/arm-smmu-v3/arm-smmu-v3.c
> > +++ b/drivers/iommu/arm/arm-smmu-v3/arm-smmu-v3.c
> > @@ -1895,18 +1895,23 @@ static void __arm_smmu_tlb_inv_range(struct
> > arm_smmu_cmdq_ent *cmd,
> >          /* Get the leaf page size */
> >          tg = __ffs(smmu_domain->domain.pgsize_bitmap);
> >
> > +        num_pages = size >> tg;
> > +
> >          /* Convert page size of 12,14,16 (log2) to 1,2,3 */
> >          cmd->tlbi.tg = (tg - 10) / 2;
> >
> >          /*
> > -         * Determine what level the granule is at. For non-leaf,
> > io-pgtable
> > -         * assumes .tlb_flush_walk can invalidate multiple levels at once,
> > -         * so ignore the nominal last-level granule and leave TTL=0.
> > +         * Determine what level the granule is at. For non-leaf, both
> > +         * io-pgtable and SVA pass a nominal last-level granule because
> > +         * they don't know what level(s) actually apply, so ignore that
> > +         * and leave TTL=0. However for various errata reasons we still
> > +         * want to use a range command, so avoid the SVA corner case
> > +         * where both scale and num could be 0 as well.
> >           */
> >          if (cmd->tlbi.leaf)
> >              cmd->tlbi.ttl = 4 - ((ilog2(granule) - 3) / (tg - 3));
> > -
> > -        num_pages = size >> tg;
> > +        else if ((num_pages & CMDQ_TLBI_RANGE_NUM_MAX) == 1)
> > +            num_pages++;
> >      }
> >
> >      cmds.num = 0;
> >