From: Andrei Dulea <adulea@amazon.de>
Date: Fri, 13 Sep 2019 16:42:29 +0200
Subject: iommu/amd: Fix downgrading default page-sizes in alloc_pte()
Git-commit: 6ccb72f8374e17d60b58a7bfd5570496332c54e2
Patch-mainline: 5.4-rc1
References: bnc#1151927 5.3.6

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@amazon.de>
Signed-off-by: Jiri Slaby <jslaby@suse.cz>
---
 drivers/iommu/amd_iommu.c |    3 ++-
 1 file changed, 2 insertions(+), 1 deletion(-)

--- a/drivers/iommu/amd_iommu.c
+++ b/drivers/iommu/amd_iommu.c
@@ -1490,6 +1490,7 @@ static u64 *alloc_pte(struct protection_
 		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_
 			/* 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;