Re: A problem of Intel IOMMU hardware ？

[Lu Baolu <baolu.lu@linux.intel.com>]

Hi Nadav,

On 3/18/21 2:12 AM, Nadav Amit wrote:
> 
> 
>> On Mar 17, 2021, at 2:35 AM, Longpeng (Mike, Cloud Infrastructure Service Product Dept.) <longpeng2@huawei.com> wrote:
>>
>> Hi Nadav,
>>
>>> -----Original Message-----
>>> From: Nadav Amit [mailto:nadav.amit@gmail.com]
>>>>   reproduce the problem with high probability (~50%).
>>>
>>> I saw Lu replied, and he is much more knowledgable than I am (I was just intrigued
>>> by your email).
>>>
>>> However, if I were you I would try also to remove some “optimizations” to look for
>>> the root-cause (e.g., use domain specific invalidations instead of page-specific).
>>>
>>
>> Good suggestion! But we did it these days, we tried to use global invalidations as follow:
>> 		iommu->flush.flush_iotlb(iommu, did, 0, 0,
>> 						DMA_TLB_DSI_FLUSH);
>> But can not resolve the problem.
>>
>>> The first thing that comes to my mind is the invalidation hint (ih) in
>>> iommu_flush_iotlb_psi(). I would remove it to see whether you get the failure
>>> without it.
>>
>> We also notice the IH, but the IH is always ZERO in our case, as the spec says:
>> '''
>> Paging-structure-cache entries caching second-level mappings associated with the specified
>> domain-id and the second-level-input-address range are invalidated, if the Invalidation Hint
>> (IH) field is Clear.
>> '''
>>
>> It seems the software is everything fine, so we've no choice but to suspect the hardware.
> 
> Ok, I am pretty much out of ideas. I have two more suggestions, but
> they are much less likely to help. Yet, they can further help to rule
> out software bugs:
> 
> 1. dma_clear_pte() seems to be wrong IMHO. It should have used WRITE_ONCE()
> to prevent split-write, which might potentially cause “invalid” (partially
> cleared) PTE to be stored in the TLB. Having said that, the subsequent
> IOTLB flush should have prevented the problem.

Agreed. The pte read/write should use READ/WRITE_ONCE() instead.

> 
> 2. Consider ensuring that the problem is not somehow related to queued
> invalidations. Try to use __iommu_flush_iotlb() instead of
> qi_flush_iotlb().
> 
> Regards,
> Nadav
> 

Best regards,
baolu