[Xen-changelog] [xen stable-4.9] AMD/IOMMU: don't needlessly trigger errors/crashes when unmapping a page

[patchbot@xxxxxxx]

commit 4b6942703dc8072fffa0d8f75169f304746abe2b
Author:     Jan Beulich <jbeulich@xxxxxxxx>
AuthorDate: Wed Dec 11 15:49:49 2019 +0100
Commit:     Jan Beulich <jbeulich@xxxxxxxx>
CommitDate: Wed Dec 11 15:49:49 2019 +0100

    AMD/IOMMU: don't needlessly trigger errors/crashes when unmapping a page
    
    Unmapping a page which has never been mapped should be a no-op (note how
    it already is in case there was no root page table allocated). There's
    in particular no need to grow the number of page table levels in use,
    and there's also no need to allocate intermediate page tables except
    when needing to split a large page.
    
    Signed-off-by: Jan Beulich <jbeulich@xxxxxxxx>
    Reviewed-by: Paul Durrant <paul@xxxxxxx>
    Acked-by: Andrew Cooper <andrew.cooper3@xxxxxxxxxx>
    master commit: ad591454f069647c36a7daaa9ec23384c0263f0b
    master date: 2019-11-12 11:08:34 +0100
---
 xen/drivers/passthrough/amd/iommu_map.c | 39 +++++++++++++++------------------
 1 file changed, 18 insertions(+), 21 deletions(-)

diff --git a/xen/drivers/passthrough/amd/iommu_map.c 
b/xen/drivers/passthrough/amd/iommu_map.c
index 8f2b06bf54..3476644826 100644
--- a/xen/drivers/passthrough/amd/iommu_map.c
+++ b/xen/drivers/passthrough/amd/iommu_map.c
@@ -456,7 +456,7 @@ static int iommu_merge_pages(struct domain *d, unsigned 
long pt_mfn,
  * page tables.
  */
 static int iommu_pde_from_gfn(struct domain *d, unsigned long pfn, 
-                              unsigned long pt_mfn[])
+                              unsigned long pt_mfn[], bool map)
 {
     u64 *pde, *next_table_vaddr;
     unsigned long  next_table_mfn;
@@ -470,6 +470,13 @@ static int iommu_pde_from_gfn(struct domain *d, unsigned 
long pfn,
     BUG_ON( table == NULL || level < IOMMU_PAGING_MODE_LEVEL_1 || 
             level > IOMMU_PAGING_MODE_LEVEL_6 );
 
+    /*
+     * A frame number past what the current page tables can represent can't
+     * possibly have a mapping.
+     */
+    if ( pfn >> (PTE_PER_TABLE_SHIFT * level) )
+        return 0;
+
     next_table_mfn = page_to_mfn(table);
 
     if ( level == IOMMU_PAGING_MODE_LEVEL_1 )
@@ -530,6 +537,9 @@ static int iommu_pde_from_gfn(struct domain *d, unsigned 
long pfn,
         /* Install lower level page table for non-present entries */
         else if ( !iommu_is_pte_present((u32*)pde) )
         {
+            if ( !map )
+                return 0;
+
             if ( next_table_mfn == 0 )
             {
                 table = alloc_amd_iommu_pgtable();
@@ -688,7 +698,7 @@ int amd_iommu_map_page(struct domain *d, unsigned long gfn, 
unsigned long mfn,
         }
     }
 
-    if ( iommu_pde_from_gfn(d, gfn, pt_mfn) || (pt_mfn[1] == 0) )
+    if ( iommu_pde_from_gfn(d, gfn, pt_mfn, true) || (pt_mfn[1] == 0) )
     {
         spin_unlock(&hd->arch.mapping_lock);
         AMD_IOMMU_DEBUG("Invalid IO pagetable entry gfn = %lx\n", gfn);
@@ -767,23 +777,7 @@ int amd_iommu_unmap_page(struct domain *d, unsigned long 
gfn)
         return 0;
     }
 
-    /* Since HVM domain is initialized with 2 level IO page table,
-     * we might need a deeper page table for lager gfn now */
-    if ( is_hvm_domain(d) )
-    {
-        int rc = update_paging_mode(d, gfn);
-
-        if ( rc )
-        {
-            spin_unlock(&hd->arch.mapping_lock);
-            AMD_IOMMU_DEBUG("Update page mode failed gfn = %lx\n", gfn);
-            if ( rc != -EADDRNOTAVAIL )
-                domain_crash(d);
-            return rc;
-        }
-    }
-
-    if ( iommu_pde_from_gfn(d, gfn, pt_mfn) || (pt_mfn[1] == 0) )
+    if ( iommu_pde_from_gfn(d, gfn, pt_mfn, false) )
     {
         spin_unlock(&hd->arch.mapping_lock);
         AMD_IOMMU_DEBUG("Invalid IO pagetable entry gfn = %lx\n", gfn);
@@ -791,8 +785,11 @@ int amd_iommu_unmap_page(struct domain *d, unsigned long 
gfn)
         return -EFAULT;
     }
 
-    /* mark PTE as 'page not present' */
-    clear_iommu_pte_present(pt_mfn[1], gfn);
+    if ( pt_mfn[1] )
+    {
+        /* 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;
--
generated by git-patchbot for /home/xen/git/xen.git#stable-4.9

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