AMD/IOMMU: suppress PTE merging after initial table creation

The logic is not fit for this purpose, so simply disable its use until
it can be fixed / replaced. Note that this re-enables merging for the
table creation case, which was disabled as a (perhaps unintended) side
effect of the earlier "amd/iommu: fix flush checks". It relies on no
page getting mapped more than once (with different properties) in this
process, as that would still be beyond what the merging logic can cope
with. But arch_iommu_populate_page_table() guarantees this afaict.

This is part of XSA-275.

Signed-off-by: Jan Beulich <jbeulich@suse.com>
master commit: 937ef32565fa3a81fdb37b9dd5aa99a1b87afa75
master date: 2018-11-20 14:55:14 +0100

diff --git a/xen/drivers/passthrough/amd/iommu_map.c b/xen/drivers/passthrough/amd/iommu_map.c
index 8537bbea4c61821ed914767a890282473d47124c..3191da91ef9faec59f603b3d2ec8870039bfc82e 100644 (file)
--- a/xen/drivers/passthrough/amd/iommu_map.c
+++ b/xen/drivers/passthrough/amd/iommu_map.c
@@ -702,11 +702,24 @@ int amd_iommu_map_page(struct domain *d, unsigned long gfn, unsigned long mfn,
                                        !!(flags & IOMMUF_writable),
                                        !!(flags & IOMMUF_readable));
 
-    /* Do not increase pde count if io mapping has not been changed */
-    if ( !need_flush )
-        goto out;
+    if ( need_flush )
+    {
+        amd_iommu_flush_pages(d, gfn, 0);
+        /* No further merging, as the logic doesn't cope. */
+        hd->arch.no_merge = true;
+    }
 
-    amd_iommu_flush_pages(d, gfn, 0);
+    /*
+     * Suppress merging of non-R/W mappings or after initial table creation,
+     * as the merge logic does not cope with this.
+     */
+    if ( hd->arch.no_merge || flags != (IOMMUF_writable | IOMMUF_readable) )
+        goto out;
+    if ( d->creation_finished )
+    {
+        hd->arch.no_merge = true;
+        goto out;
+    }
 
     for ( merge_level = IOMMU_PAGING_MODE_LEVEL_2;
           merge_level <= hd->arch.paging_mode; merge_level++ )
@@ -780,6 +793,10 @@ int amd_iommu_unmap_page(struct domain *d, unsigned long gfn)
 
     /* mark PTE as 'page not present' */
     clear_iommu_pte_present(pt_mfn[1], gfn);
+
+    /* No further merging in amd_iommu_map_page(), as the logic doesn't cope. */
+    hd->arch.no_merge = true;
+
     spin_unlock(&hd->arch.mapping_lock);
 
     amd_iommu_flush_pages(d, gfn, 0);

diff --git a/xen/include/asm-x86/iommu.h b/xen/include/asm-x86/iommu.h
index 14ad0489a6814db2b63014b5a9cf4313d623976c..dcf2e21402236e7d04a7cf892ebee06053acd333 100644 (file)
--- a/xen/include/asm-x86/iommu.h
+++ b/xen/include/asm-x86/iommu.h
@@ -40,6 +40,7 @@ struct arch_iommu
 
     /* amd iommu support */
     int paging_mode;
+    bool no_merge;
     struct page_info *root_table;
     struct guest_iommu *g_iommu;
 };