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

On 3/31/21 1:36 PM, isaacm@codeaurora.org wrote:

On 2021-03-30 21:47, Lu Baolu wrote:

quoted

On 3/31/21 11:00 AM, Isaac J. Manjarres wrote:

quoted

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 <redacted>
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?

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

Best regards,
baolu

quoted

quoted

      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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