iommu/io-pgtable: Abstract iommu_iotlb_gather access

Previously io-pgtable merely passed the iommu_iotlb_gather pointer
through to helpers, but now it has grown its own direct dereference.
This turns out to break the build for !IOMMU_API configs where the
structure only has a dummy definition. It will probably also crash
drivers who don't use the gather mechanism and simply pass in NULL.

Wrap this dereference in a suitable helper which can both be stubbed
out for !IOMMU_API and encapsulate a NULL check otherwise.

Fixes: 7a7c5bad ("iommu: Indicate queued flushes via gather data")
Reported-by: kernel test robot <lkp@intel.com>
Signed-off-by: Robin Murphy <robin.murphy@arm.com>
Link: https://lore.kernel.org/r/83672ee76f6405c82845a55c148fa836f56fbbc1.1629465282.git.robin.murphy@arm.comSigned-off-by: Joerg Roedel <jroedel@suse.de>

drivers/iommu/io-pgtable-arm-v7s.c

@@ -700,7 +700,7 @@ static size_t __arm_v7s_unmap(struct arm_v7s_io_pgtable *data,
 						ARM_V7S_BLOCK_SIZE(lvl + 1));
 				ptep = iopte_deref(pte[i], lvl, data);
 				__arm_v7s_free_table(ptep, lvl + 1, data);
-			} else if (!gather->queued) {
+			} else if (!iommu_iotlb_gather_queued(gather)) {
 				io_pgtable_tlb_add_page(iop, gather, iova, blk_size);
 			}
 			iova += blk_size;

drivers/iommu/io-pgtable-arm.c

@@ -638,7 +638,7 @@ static size_t __arm_lpae_unmap(struct arm_lpae_io_pgtable *data,
 				io_pgtable_tlb_flush_walk(iop, iova + i * size, size,
 							  ARM_LPAE_GRANULE(data));
 				__arm_lpae_free_pgtable(data, lvl + 1, iopte_deref(pte, data));
-			} else if (!gather->queued) {
+			} else if (!iommu_iotlb_gather_queued(gather)) {
 				io_pgtable_tlb_add_page(iop, gather, iova + i * size, size);
 			}
 

include/linux/iommu.h

@@ -548,6 +548,11 @@ static inline void iommu_iotlb_gather_add_page(struct iommu_domain *domain,
 		gather->start = start;
 }
 
+static inline bool iommu_iotlb_gather_queued(struct iommu_iotlb_gather *gather)
+{
+	return gather && gather->queued;
+}
+
 /* PCI device grouping function */
 extern struct iommu_group *pci_device_group(struct device *dev);
 /* Generic device grouping function */
@@ -896,6 +901,11 @@ static inline void iommu_iotlb_gather_add_page(struct iommu_domain *domain,
 {
 }
 
+static inline bool iommu_iotlb_gather_queued(struct iommu_iotlb_gather *gather)
+{
+	return false;
+}
+
 static inline void iommu_device_unregister(struct iommu_device *iommu)
 {
 }