iommu/riscv: Remove overflows on the invalidation path

Since RISC-V supports a sign extended page table it should support
a gather->end of ULONG_MAX, but if this happens it will infinite loop
because of the overflow.

Also avoid overflow computing the length by moving the +1 to the other
side of the <

Fixes: 488ffbf ("iommu/riscv: Paging domain support")
Signed-off-by: Jason Gunthorpe <jgg@nvidia.com>
Signed-off-by: Joerg Roedel <joerg.roedel@amd.com>

Author: jgunthorpe

drivers/iommu/riscv/iommu.c

@@ -931,8 +931,6 @@ static void riscv_iommu_iotlb_inval(struct riscv_iommu_domain *domain,
 	struct riscv_iommu_bond *bond;
 	struct riscv_iommu_device *iommu, *prev;
 	struct riscv_iommu_command cmd;
-	unsigned long len = end - start + 1;
-	unsigned long iova;
 
 	/*
 	 * For each IOMMU linked with this protection domain (via bonds->dev),
@@ -975,11 +973,14 @@ static void riscv_iommu_iotlb_inval(struct riscv_iommu_domain *domain,
 
 		riscv_iommu_cmd_inval_vma(&cmd);
 		riscv_iommu_cmd_inval_set_pscid(&cmd, domain->pscid);
-		if (len && len < RISCV_IOMMU_IOTLB_INVAL_LIMIT) {
-			for (iova = start; iova < end; iova += PAGE_SIZE) {
+		if (end - start < RISCV_IOMMU_IOTLB_INVAL_LIMIT - 1) {
+			unsigned long iova = start;
+
+			do {
 				riscv_iommu_cmd_inval_set_addr(&cmd, iova);
 				riscv_iommu_cmd_send(iommu, &cmd);
-			}
+			} while (!check_add_overflow(iova, PAGE_SIZE, &iova) &&
+				 iova < end);
 		} else {
 			riscv_iommu_cmd_send(iommu, &cmd);
 		}