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

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Date:   Sun, 6 Aug 2023 13:28:04 +0800
From:   zhurui <zhurui3@...wei.com>
To:     Nicolin Chen <nicolinc@...dia.com>, Will Deacon <will@...nel.org>
CC:     <linux-arm-kernel@...ts.infradead.org>, <iommu@...ts.linux.dev>,
        <linux-kernel@...r.kernel.org>,
        Robin Murphy <robin.murphy@....com>,
        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 2023/8/5 2:30, Nicolin Chen wrote:
> On Fri, Aug 04, 2023 at 05:52:25PM +0100, Will Deacon wrote:
>> On Fri, Aug 04, 2023 at 05:31:20PM +0800, zhurui wrote:
>>> When tg != 0 but ttl, scale, num all 0 in a range tlbi command, it
>>> is reserved and will cause the CERROR_ILL error. This case means
>>> that the size to be invalidated is only one page size, and the
>>> range invalidation is meaningless here. So we set tg to 0 in this
>>> case to do an non-range invalidation instead.
> 
>>> @@ -1930,6 +1927,12 @@ static void __arm_smmu_tlb_inv_range(struct arm_smmu_cmdq_ent *cmd,
>>>                         num = (num_pages >> scale) & CMDQ_TLBI_RANGE_NUM_MAX;
>>>                         cmd->tlbi.num = num - 1;
>>>
>>> +                       /* Prevent error caused by one page tlbi with leaf 0 */
>>> +                       if (scale == 0 && num == 1 && cmd->tlbi.leaf == 0)
>>> +                               cmd->tlbi.tg = 0;
>>
>> This should only be true for the last iteration, right (i.e. when num_pages
>> == 1)? In which case, I'd prefer to leave the old code as-is and just add:
>>
>>         /* Single-page leaf invalidation requires a TG field of 0 */
>>         if (num_pages == 1 && !cmd->tlbi.leaf)
>>                 cmd->tlbi.tg = 0;To Will and Nicolin,

Not only the last iteration, it's the result of __ffs function. For example, if
numpages is 33, then the value of __ffs(num_pages) is 0, so the value of scale
is also 0. The value of num depends on CMDQ_TLBI_RANGE_NUM_MAX. That is, the
maximum value of num is 31. Therefore, the final value of num is 1.
So, if consider CMDQ_TLBI_RANGE_NUM_MAX, there will be some case not the last
one page but the beginning pages. That's why I use scale and num as conditions,
not num_pages. Then I should reassign tg based on the result.

> 
> Is "!cmd->tlbi.leaf" to be "leaf" or "non-leaf"?
> 
> IIUIC, this "num_pages == 1" implies "NUM == 0, SCALE == 0" while
> the "!cmd->tlbi.leaf" implies "TTL = 0b00", which in combination
> would result in a CERROR_ILL mentioned by the spec?
> 
> I feel this could be more clear by just checking the three fields
> following the spec...>
> Thanks
> Nicolin
> .
> 
Yes, based on spec 4.4.1.1 for ARM IHI 0070, after the TLL and TG table, there is a
description for TG != 0b00, and you can check it in the last point.

Thanks.
ZhuRui
.