x86/p2m-pt: tighten conditions of IOMMU mapping updates

Whether the MFN changes does not depend on the new entry being valid
(but solely on the old one), and the need to update or TLB-flush also
depends on permission changes.

Signed-off-by: Jan Beulich <jbeulich@suse.com>
Reviewed-by: Andrew Cooper <andrew.cooper3@citrix.com>
Reviewed-by: George Dunlap <george.dunlap@citrix.com>

diff --git a/xen/arch/x86/mm/p2m-pt.c b/xen/arch/x86/mm/p2m-pt.c
index e61d5033d38e6270eb29ebae1f08e2803a568adf..9621eb1ce33f295a2518f4c8a8c64c0de33b290c 100644 (file)
--- a/xen/arch/x86/mm/p2m-pt.c
+++ b/xen/arch/x86/mm/p2m-pt.c
@@ -494,7 +494,18 @@ p2m_pt_set_entry(struct p2m_domain *p2m, unsigned long gfn, mfn_t mfn,
     l3_pgentry_t l3e_content;
     int rc;
     unsigned int iommu_pte_flags = p2m_get_iommu_flags(p2mt);
-    unsigned long old_mfn = 0;
+    /*
+     * old_mfn and iommu_old_flags control possible flush/update needs on the
+     * IOMMU: We need to flush when MFN or flags (i.e. permissions) change.
+     * iommu_old_flags being initialized to zero covers the case of the entry
+     * getting replaced being a non-present (leaf or intermediate) one. For
+     * present leaf entries the real value will get calculated below, while
+     * for present intermediate entries ~0 (guaranteed != iommu_pte_flags)
+     * will be used (to cover all cases of what the leaf entries underneath
+     * the intermediate one might be).
+     */
+    unsigned int flags, iommu_old_flags = 0;
+    unsigned long old_mfn = INVALID_MFN;
 
     ASSERT(sve != 0);
 
@@ -543,12 +554,20 @@ p2m_pt_set_entry(struct p2m_domain *p2m, unsigned long gfn, mfn_t mfn,
                                    L3_PAGETABLE_SHIFT - PAGE_SHIFT,
                                    L3_PAGETABLE_ENTRIES);
         ASSERT(p2m_entry);
-        if ( (l1e_get_flags(*p2m_entry) & _PAGE_PRESENT) &&
-             !(l1e_get_flags(*p2m_entry) & _PAGE_PSE) )
+        flags = l1e_get_flags(*p2m_entry);
+        if ( flags & _PAGE_PRESENT )
         {
-            /* We're replacing a non-SP page with a superpage.  Make sure to
-             * handle freeing the table properly. */
-            intermediate_entry = *p2m_entry;
+            if ( flags & _PAGE_PSE )
+            {
+                iommu_old_flags =
+                    p2m_get_iommu_flags(p2m_flags_to_type(flags));
+                old_mfn = l1e_get_pfn(*p2m_entry);
+            }
+            else
+            {
+                iommu_old_flags = ~0;
+                intermediate_entry = *p2m_entry;
+            }
         }
 
         ASSERT(!mfn_valid(mfn) || p2mt != p2m_mmio_direct);
@@ -559,10 +578,7 @@ p2m_pt_set_entry(struct p2m_domain *p2m, unsigned long gfn, mfn_t mfn,
         entry_content.l1 = l3e_content.l3;
 
         if ( entry_content.l1 != 0 )
-        {
             p2m_add_iommu_flags(&entry_content, 0, iommu_pte_flags);
-            old_mfn = l1e_get_pfn(*p2m_entry);
-        }
 
         p2m->write_p2m_entry(p2m, gfn, p2m_entry, entry_content, 3);
         /* NB: paging_write_p2m_entry() handles tlb flushes properly */
@@ -587,7 +603,10 @@ p2m_pt_set_entry(struct p2m_domain *p2m, unsigned long gfn, mfn_t mfn,
         p2m_entry = p2m_find_entry(table, &gfn_remainder, gfn,
                                    0, L1_PAGETABLE_ENTRIES);
         ASSERT(p2m_entry);
-        
+        iommu_old_flags =
+            p2m_get_iommu_flags(p2m_flags_to_type(l1e_get_flags(*p2m_entry)));
+        old_mfn = l1e_get_pfn(*p2m_entry);
+
         if ( mfn_valid(mfn) || (p2mt == p2m_mmio_direct)
                             || p2m_is_paging(p2mt) )
             entry_content = p2m_l1e_from_pfn(mfn_x(mfn),
@@ -596,10 +615,8 @@ p2m_pt_set_entry(struct p2m_domain *p2m, unsigned long gfn, mfn_t mfn,
             entry_content = l1e_empty();
 
         if ( entry_content.l1 != 0 )
-        {
             p2m_add_iommu_flags(&entry_content, 0, iommu_pte_flags);
-            old_mfn = l1e_get_pfn(*p2m_entry);
-        }
+
         /* level 1 entry */
         p2m->write_p2m_entry(p2m, gfn, p2m_entry, entry_content, 1);
         /* NB: paging_write_p2m_entry() handles tlb flushes properly */
@@ -610,14 +627,20 @@ p2m_pt_set_entry(struct p2m_domain *p2m, unsigned long gfn, mfn_t mfn,
                                    L2_PAGETABLE_SHIFT - PAGE_SHIFT,
                                    L2_PAGETABLE_ENTRIES);
         ASSERT(p2m_entry);
-        
-        /* FIXME: Deal with 4k replaced by 2meg pages */
-        if ( (l1e_get_flags(*p2m_entry) & _PAGE_PRESENT) &&
-             !(l1e_get_flags(*p2m_entry) & _PAGE_PSE) )
+        flags = l1e_get_flags(*p2m_entry);
+        if ( flags & _PAGE_PRESENT )
         {
-            /* We're replacing a non-SP page with a superpage.  Make sure to
-             * handle freeing the table properly. */
-            intermediate_entry = *p2m_entry;
+            if ( flags & _PAGE_PSE )
+            {
+                iommu_old_flags =
+                    p2m_get_iommu_flags(p2m_flags_to_type(flags));
+                old_mfn = l1e_get_pfn(*p2m_entry);
+            }
+            else
+            {
+                iommu_old_flags = ~0;
+                intermediate_entry = *p2m_entry;
+            }
         }
         
         ASSERT(!mfn_valid(mfn) || p2mt != p2m_mmio_direct);
@@ -631,10 +654,7 @@ p2m_pt_set_entry(struct p2m_domain *p2m, unsigned long gfn, mfn_t mfn,
         entry_content.l1 = l2e_content.l2;
 
         if ( entry_content.l1 != 0 )
-        {
             p2m_add_iommu_flags(&entry_content, 0, iommu_pte_flags);
-            old_mfn = l1e_get_pfn(*p2m_entry);
-        }
 
         p2m->write_p2m_entry(p2m, gfn, p2m_entry, entry_content, 2);
         /* NB: paging_write_p2m_entry() handles tlb flushes properly */
@@ -645,11 +665,12 @@ p2m_pt_set_entry(struct p2m_domain *p2m, unsigned long gfn, mfn_t mfn,
          && (gfn + (1UL << page_order) - 1 > p2m->max_mapped_pfn) )
         p2m->max_mapped_pfn = gfn + (1UL << page_order) - 1;
 
-    if ( iommu_enabled && need_iommu(p2m->domain) )
+    if ( iommu_enabled && need_iommu(p2m->domain) &&
+         (iommu_old_flags != iommu_pte_flags || old_mfn != mfn_x(mfn)) )
     {
         if ( iommu_use_hap_pt(p2m->domain) )
         {
-            if ( old_mfn && (old_mfn != mfn_x(mfn)) )
+            if ( iommu_old_flags )
                 amd_iommu_flush_pages(p2m->domain, gfn, page_order);
         }
         else