Messages in this thread | | | Subject | Re: [PATCH v2 1/1] iommu/arm-smmu-v3: Fix error case of range command | From | zhurui <> | Date | Wed, 9 Aug 2023 17:22:06 +0800 |
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On 2023/8/9 0:43, Robin Murphy wrote: > On 08/08/2023 5:24 pm, Will Deacon wrote: >> Hi Robin, >> >> On Mon, Aug 07, 2023 at 08:20:45PM +0100, Robin Murphy wrote: >>> On 2023-08-06 06:28, zhurui wrote: >>>> 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. >>> >>> Yeah, I'd rather not downgrade to a non-range invalidate since that >>> complicates the reasoning for the errata affecting those. If the size of the >>> invalidation is equal to TG then it can only represent a single last-level >>> page, i.e. TTL=3, thus if it does warrant handling here then indeed >>> rearranging to base the condition on num_pages as well ought to suffice. >>> However, this is all still begging the question of where and why we're doing >>> a *non-leaf* invalidation that isn't aligned to the size of a table, because >>> that in itself doesn't make a whole heap of sense - my hunch is that that >>> wants figuring out and could probably be fixed at the source. >> >> Isn't that described above because we're using CMDQ_TLBI_RANGE_NUM_MAX >> to break up the range into separate commands? > > Not really, because if we're doing a genuine non-leaf invalidation of a table then it should be a block-aligned range that ought to fit in a single command and should certainly never involve a single-granule remainder. If we're doing non-leaf invalidations of things that logically don't need to be non-leaf, making them leaf would be the even better option. >
I agree with Robin that if the caller is doing a genuine non-leaf invalidation of a table, it should not involve a single-granule tlbi. It seems that the caller only filter the block size, but not the address aligned or not maybe.
>> Do you mind if I queue the patch as-is for now? I don't think the driver >> should be emitting illegal commands, and v2 of the patch does seem like >> the obvious thing to do. > > TBH I'd rather you just drop my patch if it's proven problematic, and I'll take another crack at it soon. The potential problems we introduce by using non-range invalidates on errata-affected MMU-700 revisions are worse than the almost-entirely-theoretical one I was trying to address. >
If you all agree to roll back the problematic code, is the first patch be OK? Should I need to add some more descriptions to clarify this?
Thanks, Zhurui.
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