[RFC PATCH v1] iommu/io-pgtable-arm: Check for leaf entry right after finding it

[olekstysh@gmail.com (Oleksandr Tyshchenko)]

From: Oleksandr Tyshchenko <oleksandr_tyshchenko@epam.com>

Do a check for already installed leaf entry at the current level before
performing any actions when trying to map.

This check is already present in arm_lpae_init_pte(), i.e. before
installing new leaf entry at the current level if conditions to do so
are met (size == block_size).

But, this might be insufficient in case when we have already
installed block mapping at this level and it is not time to
install new leaf entry (size != block_size).
In that case we continue walking the page table down with wrong pointer
to the next level.

So, move check from arm_lpae_init_pte() to __arm_lpae_map() in order to
avoid all cases.

Signed-off-by: Oleksandr Tyshchenko <oleksandr_tyshchenko@epam.com>
---
I hope that following actions can help to catch it:
1. Call iommu_map for a block mapping (e.g. 2M) at some address
   (e.g. iova 0x80000000 pa 0x80000000).
2. Call iommu_map for a page mapping (4k) at some address from
   the previous mapped region (e.g. iova 0x80008000 pa 0x90000000).

I understand that after iommu_map should be iommu_unmap, but
different scenarios may occur).
---
---
 drivers/iommu/io-pgtable-arm.c | 13 ++++++++-----
 1 file changed, 8 insertions(+), 5 deletions(-)

diff --git a/drivers/iommu/io-pgtable-arm.c b/drivers/iommu/io-pgtable-arm.c
index f5c90e1..ebdb82f 100644
--- a/drivers/iommu/io-pgtable-arm.c
+++ b/drivers/iommu/io-pgtable-arm.c
@@ -272,11 +272,7 @@ static int arm_lpae_init_pte(struct arm_lpae_io_pgtable *data,
 	arm_lpae_iopte pte = prot;
 	struct io_pgtable_cfg *cfg = &data->iop.cfg;
 
-	if (iopte_leaf(*ptep, lvl)) {
-		/* We require an unmap first */
-		WARN_ON(!selftest_running);
-		return -EEXIST;
-	} else if (iopte_type(*ptep, lvl) == ARM_LPAE_PTE_TYPE_TABLE) {
+	if (iopte_type(*ptep, lvl) == ARM_LPAE_PTE_TYPE_TABLE) {
 		/*
 		 * We need to unmap and free the old table before
 		 * overwriting it with a block entry.
@@ -315,6 +311,13 @@ static int __arm_lpae_map(struct arm_lpae_io_pgtable *data, unsigned long iova,
 	/* Find our entry at the current level */
 	ptep += ARM_LPAE_LVL_IDX(iova, lvl, data);
 
+	/* Check for already installed leaf entry */
+	if (iopte_leaf(*ptep, lvl)) {
+		/* We require an unmap first */
+		WARN_ON(!selftest_running);
+		return -EEXIST;
+	}
+
 	/* If we can install a leaf entry at this level, then do so */
 	if (size == block_size && (size & cfg->pgsize_bitmap))
 		return arm_lpae_init_pte(data, iova, paddr, prot, lvl, ptep);
-- 
2.7.4