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

[isaacm@codeaurora.org]

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@codeaurora.org>
>> Suggested-by: Will Deacon <will@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?
> 
>>   	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
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