[PATCH 5.3 115/148] iommu/amd: Fix downgrading default page-sizes in alloc_pte()

[Greg Kroah-Hartman]

From: Andrei Dulea <adulea@xxxxxxxxx>

[ Upstream commit 6ccb72f8374e17d60b58a7bfd5570496332c54e2 ]

Downgrading an existing large mapping to a mapping using smaller
page-sizes works only for the mappings created with page-mode 7 (i.e.
non-default page size).

Treat large mappings created with page-mode 0 (i.e. default page size)
like a non-present mapping and allow to overwrite it in alloc_pte().

While around, make sure that we flush the TLB only if we change an
existing mapping, otherwise we might end up acting on garbage PTEs.

Fixes: 6d568ef9a622 ("iommu/amd: Allow downgrading page-sizes in alloc_pte()")
Signed-off-by: Andrei Dulea <adulea@xxxxxxxxx>
Signed-off-by: Sasha Levin <sashal@xxxxxxxxxx>
---
 drivers/iommu/amd_iommu.c | 3 ++-
 1 file changed, 2 insertions(+), 1 deletion(-)

diff --git a/drivers/iommu/amd_iommu.c b/drivers/iommu/amd_iommu.c
index e1259429ded2f..3b1d7ae6f75e0 100644
--- a/drivers/iommu/amd_iommu.c
+++ b/drivers/iommu/amd_iommu.c
@@ -1490,6 +1490,7 @@ static u64 *alloc_pte(struct protection_domain *domain,
 		pte_level = PM_PTE_LEVEL(__pte);
 
 		if (!IOMMU_PTE_PRESENT(__pte) ||
+		    pte_level == PAGE_MODE_NONE ||
 		    pte_level == PAGE_MODE_7_LEVEL) {
 			page = (u64 *)get_zeroed_page(gfp);
 			if (!page)
@@ -1500,7 +1501,7 @@ static u64 *alloc_pte(struct protection_domain *domain,
 			/* pte could have been changed somewhere. */
 			if (cmpxchg64(pte, __pte, __npte) != __pte)
 				free_page((unsigned long)page);
-			else if (pte_level == PAGE_MODE_7_LEVEL)
+			else if (IOMMU_PTE_PRESENT(__pte))
 				domain->updated = true;
 
 			continue;
-- 
2.20.1