iommu/amd: Fix downgrading default page-sizes in alloc_pte()

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>

diff --git a/drivers/iommu/amd_iommu.c b/drivers/iommu/amd_iommu.c
index 1385474..c7e28a8 100644 (file)
--- 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;