[PATCH v2 02/14] powerpc/pseries/iommu: Makes sure IOMMU_PAGE_SIZE <= PAGE_SIZE

[Leonardo Bras <leobras.c@gmail.com>]

Cc: linuxppc-dev@lists.ozlabs.org, linux-kernel@vger.kernel.org, 

Having System pagesize < IOMMU pagesize may cause a page owned by another
process/VM to be written by a buggy driver / device.

As it's intended to use DDW for indirect mapping, it's possible to get
a configuration where (PAGE_SIZE = 4k) < (IOMMU_PAGE_SIZE() = 64k).

To avoid this, make sure create_ddw() can only use pagesize <= PAGE_SIZE.

Signed-off-by: Leonardo Bras <leobras.c@gmail.com>
---
 arch/powerpc/platforms/pseries/iommu.c | 11 +++++++----
 1 file changed, 7 insertions(+), 4 deletions(-)

diff --git a/arch/powerpc/platforms/pseries/iommu.c b/arch/powerpc/platforms/pseries/iommu.c
index 9db3927607a4..4eff3a6a441e 100644
--- a/arch/powerpc/platforms/pseries/iommu.c
+++ b/arch/powerpc/platforms/pseries/iommu.c
@@ -1206,17 +1206,20 @@ static u64 enable_ddw(struct pci_dev *dev, struct device_node *pdn)
 			goto out_failed;
 		}
 	}
-	if (query.page_size & 4) {
-		page_shift = 24; /* 16MB */
-	} else if (query.page_size & 2) {
+
+	/* Choose the biggest pagesize available <= PAGE_SHIFT */
+	if ((query.page_size & 4)) {
+		page_shift = 24; /* 16MB - Hugepages */
+	} else if ((query.page_size & 2) && PAGE_SHIFT >= 16) {
 		page_shift = 16; /* 64kB */
-	} else if (query.page_size & 1) {
+	} else if ((query.page_size & 1) && PAGE_SHIFT >= 12) {
 		page_shift = 12; /* 4kB */
 	} else {
 		dev_dbg(&dev->dev, "no supported direct page size in mask %x",
 			  query.page_size);
 		goto out_failed;
 	}
+
 	/* verify the window * number of ptes will map the partition */
 	/* check largest block * page size > max memory hotplug addr */
 	max_addr = ddw_memory_hotplug_max();
-- 
2.25.4