Re: [PATCH rc 2/2] iommu: Do not return 0 from map_pages if it doesn't do anything

These three implementations of map_pages() all succeed if a mapping is
requested with no read or write. Since they return back to __iommu_map()
leaving the mapped output as 0 it triggers an infinite loop. Therefore
nothing is using no-access protection bits.

Further, VFIO and iommufd rely on iommu_iova_to_phys() to get back PFNs
stored by map, if iommu_map() succeeds but iommu_iova_to_phys() fails that
will create serious bugs.

Thus remove this never used "nothing to do" concept and just fail map
immediately.

Fixes: e5fc9753b1a8 ("iommu/io-pgtable: Add ARMv7 short descriptor support")
Fixes: e1d3c0fd701d ("iommu: add ARM LPAE page table allocator")
Fixes: 745ef1092bcf ("iommu/io-pgtable: Move Apple DART support to its own file")
Signed-off-by: Jason Gunthorpe <jgg@nvidia.com>
---
 drivers/iommu/io-pgtable-arm-v7s.c | 3 +--
 drivers/iommu/io-pgtable-arm.c     | 3 +--
 drivers/iommu/io-pgtable-dart.c    | 3 +--
 3 files changed, 3 insertions(+), 6 deletions(-)

diff --git a/drivers/iommu/io-pgtable-arm-v7s.c b/drivers/iommu/io-pgtable-arm-v7s.c
index 75f244a3e12df6..06ffc683b28fee 100644
--- a/drivers/iommu/io-pgtable-arm-v7s.c
+++ b/drivers/iommu/io-pgtable-arm-v7s.c

@@ -552,9 +552,8 @@ static int arm_v7s_map_pages(struct io_pgtable_ops *ops, unsigned long iova,
 		    paddr >= (1ULL << data->iop.cfg.oas)))
 		return -ERANGE;
 
-	/* If no access, then nothing to do */
 	if (!(prot & (IOMMU_READ | IOMMU_WRITE)))
-		return 0;
+		return -EINVAL;
 
 	while (pgcount--) {
 		ret = __arm_v7s_map(data, iova, paddr, pgsize, prot, 1, data->pgd,

diff --git a/drivers/iommu/io-pgtable-arm.c b/drivers/iommu/io-pgtable-arm.c
index f5d9fd1f45bf49..ff4149ae1751d4 100644
--- a/drivers/iommu/io-pgtable-arm.c
+++ b/drivers/iommu/io-pgtable-arm.c

@@ -515,9 +515,8 @@ static int arm_lpae_map_pages(struct io_pgtable_ops *ops, unsigned long iova,
 	if (WARN_ON(iaext || paddr >> cfg->oas))
 		return -ERANGE;
 
-	/* If no access, then nothing to do */
 	if (!(iommu_prot & (IOMMU_READ | IOMMU_WRITE)))
-		return 0;
+		return -EINVAL;