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

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Message-ID: <a71e17d8-f5c2-113b-b1ca-e2c011630850@arm.com>
Date:   Wed, 6 Sep 2023 13:59:55 +0100
From:   Robin Murphy <robin.murphy@....com>
To:     Easwar Hariharan <eahariha@...ux.microsoft.com>,
        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 2023-09-06 06:05, Easwar Hariharan wrote:
> On 8/25/23 01:12, zhurui wrote:
>> On 2023/8/19 0:21, Will Deacon wrote:
>>> 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@...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;
>>>>>
>>
>> Hi, Will and Robin,
>> Sorry for taking so long to reply you. We have some problems with our 
>> machine these days. It's
>> solved just today. I give a test with Robin's patch for our testcase, 
>> everything is ok. I think
>> the problem has been solved.
>>
>> Thanks,
>> ZhuRui.
>>
> 
> Hi Robin,
> 
> Could you please send out this patch since ZhuRui has confirmed it fixes 
> their issue and CC it to stable for v5.15+? Or if Will is willing to 
> pick it up off this thread, I can do the backport to stable.

I can resend after -rc1 if Will would prefer that. It's tagged as a fix 
so should hopefully get picked for stable automatically once it hits 
mainline.

Thanks,
Robin.