[RFC PATCH 2/5] iommu: Add an unmap_pages() op for IOMMU drivers

[Lu Baolu]

On 3/31/21 1:36 PM, isaacm at codeaurora.org wrote:
> On 2021-03-30 21:47, Lu Baolu wrote:
>> On 3/31/21 11:00 AM, Isaac J. Manjarres wrote:
>>> Add a callback for IOMMU drivers to provide a path for the
>>> IOMMU framework to call into an IOMMU driver, which can call
>>> into the io-pgtable code, to unmap a virtually contiguous
>>> range of pages of the same size.
>>>
>>> For IOMMU drivers that do not specify an unmap_pages() callback,
>>> the existing logic of unmapping memory one page block at a time
>>> will be used.
>>>
>>> Signed-off-by: Isaac J. Manjarres <isaacm at codeaurora.org>
>>> Suggested-by: Will Deacon <will at kernel.org>
>>> ---
>>>   include/linux/iommu.h | 4 ++++
>>>   1 file changed, 4 insertions(+)
>>>
>>> diff --git a/include/linux/iommu.h b/include/linux/iommu.h
>>> index 5e7fe519430a..9cf81242581a 100644
>>> --- a/include/linux/iommu.h
>>> +++ b/include/linux/iommu.h
>>> @@ -193,6 +193,7 @@ struct iommu_iotlb_gather {
>>>    * @detach_dev: detach device from an iommu domain
>>>    * @map: map a physically contiguous memory region to an iommu domain
>>>    * @unmap: unmap a physically contiguous memory region from an 
>>> iommu domain
>>> + * @unmap_pages: unmap a number of pages of the same size from an 
>>> iommu domain
>>>    * @flush_iotlb_all: Synchronously flush all hardware TLBs for this 
>>> domain
>>>    * @iotlb_sync_map: Sync mappings created recently using @map to 
>>> the hardware
>>>    * @iotlb_sync: Flush all queued ranges from the hardware TLBs and 
>>> empty flush
>>> @@ -245,6 +246,9 @@ struct iommu_ops {
>>>              phys_addr_t paddr, size_t size, int prot, gfp_t gfp);
>>>       size_t (*unmap)(struct iommu_domain *domain, unsigned long iova,
>>>                size_t size, struct iommu_iotlb_gather *iotlb_gather);
>>> +    size_t (*unmap_pages)(struct iommu_domain *domain, unsigned long 
>>> iova,
>>> +                  size_t pgsize, size_t pgcount,
>>> +                  struct iommu_iotlb_gather *iotlb_gather);
>>
>> Is it possible to add an equivalent map_pages() callback?
> Yes, map_pages() can be implemented and can leverage a lot of the 
> implementation
> of unmap_pages(). The problem is that if you map several pages in one 
> call, and then
> encounter an error and have to rollback, you should do TLB maintenance, 
> as iommu_map
> does when it encounters an error. However, we can't call iommu_unmap 
> from io-pgtable-arm
> for example. We can call arm_lpae_unmap_pages() from the later patches, 
> but that doesn't
> solve the TLB maintenance issue. Do you have any thoughts on how to 
> address this?

Call unmap_pages() with the same pages and size to roll back. Does it
work?

Best regards,
baolu

>>
>>>       void (*flush_iotlb_all)(struct iommu_domain *domain);
>>>       void (*iotlb_sync_map)(struct iommu_domain *domain, unsigned 
>>> long iova,
>>>                      size_t size);
>>>
>>
>> Best regards,
>> baolu