Re: [PATCH v2] hw/arm/smmuv3: Simplify range invalidation

[Eric Auger]

Hi,

On 9/1/21 8:33 AM, Liu, Renwei wrote:
>> -----Original Message-----
>> From: Eric Auger [mailto:eric.auger@redhat.com]
>> Sent: Tuesday, August 31, 2021 10:46 PM
>> To: Liu, Renwei; Peter Maydell
>> Cc: qemu-arm@nongnu.org; qemu-devel@nongnu.org; Li, Chunming; Wen,
>> Jianxian
>> Subject: Re: [PATCH v2] hw/arm/smmuv3: Simplify range invalidation
>>
>> Hi Liu,
>>
>> On 8/23/21 9:50 AM, Liu, Renwei wrote:
>>> Simplify range invalidation which can avoid to iterate over all
>>> iotlb entries multi-times. For instance invalidations patterns like
>>> "invalidate 32 4kB pages starting from 0xffacd000" need to iterate
>> over
>>> all iotlb entries 6 times (num_pages: 1, 2, 16, 8, 4, 1). It only
>> needs
>>> to iterate over all iotlb entries once with new implementation.
>> This wouldn't work. This reverts commit
>> 6d9cd115b9df ("hw/arm/smmuv3: Enforce invalidation on a power of two
>> range")
>> which is mandated for VFIO and virtio to work. IOTLB invalidations must
>> be naturally aligned and with a power of 2 range, hence this iteration.
>>
>> Thanks
>>
>> Eric
> Hi Eric,
>
> Could you try the patch firstly? I want to know whether it's failed
> in your application scenario with this implementation.
There are many test cases, virtio-pci, vhost, VFIO, ...
> I agree with you that IOTLB entry must be naturally aligned and
> with a power of 2 range. But we can invalidate multi IOTLB entries
> in one iteration. We check the overlap between invalidation range
> and IOTLB range, not check mask.
This smmu_hash_remove_by_asid_iova() change only affects the internal
SMMUv3 IOTLB hash table lookup. However there are also IOTLB
invalidation notifications sent to components who registered notifiers,
ie. smmuv3_notify_iova path.
>  The final result is same with
> your implementation (split to multi times with a power of 2 range).
> I wonder why we can't implement it directly when the application can
> send an invalidation command with a non power of 2 range.
> We have tested it in our application scenario and not find any fail.
Assume the driver invalidates 5 * 4kB pages =0x5000 range.  Without the
loop you removed

in smmuv3_notify_iova()  event.entry.addr_mask = num_pages * (1 <<
granule) - 1 = 0x4FFF. This addr_mask  is an invalid mask
this entry is passed to components who registered invalidation notifiers
such as vhost or vfio. for instance in VFIO you have '&' ops on the
addr_mask.
addr_mask is expected to be a mask of a power of 2 range.

Does it clarify?

Thanks

Eric
>
> In addition, from the code implementation, smmu_iotlb_inv_iova()
> should be OK. In another call smmuv3_inv_notifiers_iova() ->
> smmuv3_notify_iova() -> memory_region_notify_iommu_one(),
> it also checks range overlap. So it should be OK if the range
> is not a power of 2.
>
> Could you take a look at it again?
>
> Thanks
> Renwei Liu