[Xen-changelog] [xen staging-4.12] AMD/IOMMU: don't needlessly trigger errors/crashes when unmapping a page

[patchbot@xxxxxxx]

commit 36d2ecb9991bf2d1ddb933872c3dfbd26300ca68
Author:     Jan Beulich <jbeulich@xxxxxxxx>
AuthorDate: Mon Nov 25 16:01:00 2019 +0100
Commit:     Jan Beulich <jbeulich@xxxxxxxx>
CommitDate: Mon Nov 25 16:01:00 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 | 40 +++++++++++++++------------------
 1 file changed, 18 insertions(+), 22 deletions(-)

diff --git a/xen/drivers/passthrough/amd/iommu_map.c 
b/xen/drivers/passthrough/amd/iommu_map.c
index 67329b0c95..628aa60230 100644
--- a/xen/drivers/passthrough/amd/iommu_map.c
+++ b/xen/drivers/passthrough/amd/iommu_map.c
@@ -343,7 +343,7 @@ uint64_t amd_iommu_get_address_from_pte(void *pte)
  * page tables.
  */
 static int iommu_pde_from_dfn(struct domain *d, unsigned long dfn,
-                              unsigned long pt_mfn[])
+                              unsigned long pt_mfn[], bool map)
 {
     uint64_t *pde, *next_table_vaddr;
     unsigned long  next_table_mfn;
@@ -356,6 +356,13 @@ static int iommu_pde_from_dfn(struct domain *d, unsigned 
long dfn,
 
     BUG_ON( table == NULL || level < 1 || level > 6 );
 
+    /*
+     * A frame number past what the current page tables can represent can't
+     * possibly have a mapping.
+     */
+    if ( dfn >> (PTE_PER_TABLE_SHIFT * level) )
+        return 0;
+
     next_table_mfn = mfn_x(page_to_mfn(table));
 
     if ( level == 1 )
@@ -415,6 +422,9 @@ static int iommu_pde_from_dfn(struct domain *d, unsigned 
long dfn,
         /* Install lower level page table for non-present entries */
         else if ( !iommu_is_pte_present((uint32_t *)pde) )
         {
+            if ( !map )
+                return 0;
+
             if ( next_table_mfn == 0 )
             {
                 table = alloc_amd_iommu_pgtable();
@@ -577,7 +587,7 @@ int amd_iommu_map_page(struct domain *d, dfn_t dfn, mfn_t 
mfn,
         }
     }
 
-    if ( iommu_pde_from_dfn(d, dfn_x(dfn), pt_mfn) || (pt_mfn[1] == 0) )
+    if ( iommu_pde_from_dfn(d, dfn_x(dfn), pt_mfn, true) || (pt_mfn[1] == 0) )
     {
         spin_unlock(&hd->arch.mapping_lock);
         AMD_IOMMU_DEBUG("Invalid IO pagetable entry dfn = %"PRI_dfn"\n",
@@ -615,24 +625,7 @@ int amd_iommu_unmap_page(struct domain *d, dfn_t dfn,
         return 0;
     }
 
-    /* Since HVM domain is initialized with 2 level IO page table,
-     * we might need a deeper page table for lager dfn now */
-    if ( is_hvm_domain(d) )
-    {
-        int rc = update_paging_mode(d, dfn_x(dfn));
-
-        if ( rc )
-        {
-            spin_unlock(&hd->arch.mapping_lock);
-            AMD_IOMMU_DEBUG("Update page mode failed dfn = %"PRI_dfn"\n",
-                            dfn_x(dfn));
-            if ( rc != -EADDRNOTAVAIL )
-                domain_crash(d);
-            return rc;
-        }
-    }
-
-    if ( iommu_pde_from_dfn(d, dfn_x(dfn), pt_mfn) || (pt_mfn[1] == 0) )
+    if ( iommu_pde_from_dfn(d, dfn_x(dfn), pt_mfn, false) )
     {
         spin_unlock(&hd->arch.mapping_lock);
         AMD_IOMMU_DEBUG("Invalid IO pagetable entry dfn = %"PRI_dfn"\n",
@@ -641,8 +634,11 @@ int amd_iommu_unmap_page(struct domain *d, dfn_t dfn,
         return -EFAULT;
     }
 
-    /* mark PTE as 'page not present' */
-    *flush_flags |= clear_iommu_pte_present(pt_mfn[1], dfn_x(dfn));
+    if ( pt_mfn[1] )
+    {
+        /* Mark PTE as 'page not present'. */
+        *flush_flags |= clear_iommu_pte_present(pt_mfn[1], dfn_x(dfn));
+    }
 
     spin_unlock(&hd->arch.mapping_lock);
 
--
generated by git-patchbot for /home/xen/git/xen.git#staging-4.12

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