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

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Date:   Fri, 18 Aug 2023 17:19:31 +0100
From:   Robin Murphy <robin.murphy@....com>
To:     zhurui <zhurui3@...wei.com>, Will Deacon <will@...nel.org>
Cc:     Nicolin Chen <nicolinc@...dia.com>,
        linux-arm-kernel@...ts.infradead.org, iommu@...ts.linux.dev,
        linux-kernel@...r.kernel.org, Joerg Roedel <joro@...tes.org>,
        Lu Baolu <baolu.lu@...ux.intel.com>,
        Jason Gunthorpe <jgg@...pe.ca>,
        Yicong Yang <yangyicong@...ilicon.com>,
        Tomas Krcka <krckatom@...zon.de>,
        Jean-Philippe Brucker <jean-philippe@...aro.org>
Subject: Re: [PATCH v2 1/1] iommu/arm-smmu-v3: Fix error case of range command

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... ;)
Thanks,
Robin.

> ----->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@...wei.com>
> Signed-off-by: Robin Murphy <robin.murphy@....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;
>