[Xen-changelog] [xen master] x86/mm: re-arrange get_page_from_l<N>e() vs pv_l1tf_check_l<N>e()

[patchbot@xxxxxxx]

commit 3ac0b20bc375cfe78eb01528f2a18ac305eff6ab
Author:     Jan Beulich <jbeulich@xxxxxxxx>
AuthorDate: Thu Aug 30 11:01:02 2018 +0200
Commit:     Jan Beulich <jbeulich@xxxxxxxx>
CommitDate: Thu Aug 30 11:01:02 2018 +0200

    x86/mm: re-arrange get_page_from_l<N>e() vs pv_l1tf_check_l<N>e()
    
    Restore symmetry between get_page_from_l<N>e(): pv_l1tf_check_l<N>e() is
    now uniformly invoked from outside of them. They're no longer getting
    called for non-present PTEs. This way the slightly odd three-way return
    value meaning of the higher level ones can also be got rid of.
    
    Leave an assertion in get_page_from_l1e() as the only non-static one of
    the four siblings, to ensure that no new unguarded calls go unnoticed.
    
    Introduce local variables holding the page table entries processed, and
    use them throughout the loop bodies instead of re-reading them from the
    page table several times.
    
    Signed-off-by: Jan Beulich <jbeulich@xxxxxxxx>
    Reviewed-by: Wei Liu <wei.liu2@xxxxxxxxxx>
    Reviewed-by: Andrew Cooper <andrew.cooper3@xxxxxxxxxx>
---
 xen/arch/x86/mm.c               | 105 +++++++++++++++++++++-------------------
 xen/arch/x86/pv/ro-page-fault.c |  10 ++--
 2 files changed, 60 insertions(+), 55 deletions(-)

diff --git a/xen/arch/x86/mm.c b/xen/arch/x86/mm.c
index 8ac4412554..44ff7a6b76 100644
--- a/xen/arch/x86/mm.c
+++ b/xen/arch/x86/mm.c
@@ -900,8 +900,11 @@ get_page_from_l1e(
     struct domain *real_pg_owner;
     bool write;
 
-    if ( !(l1f & _PAGE_PRESENT) )
+    if ( unlikely(!(l1f & _PAGE_PRESENT)) )
+    {
+        ASSERT_UNREACHABLE();
         return 0;
+    }
 
     if ( unlikely(l1f & l1_disallow_mask(l1e_owner)) )
     {
@@ -1099,14 +1102,6 @@ get_page_from_l1e(
     return -EBUSY;
 }
 
-
-/* NB. Virtual address 'l2e' maps to a machine address within frame 'pfn'. */
-/*
- * get_page_from_l2e returns:
- *   1 => page not present
- *   0 => success
- *  <0 => error code
- */
 define_get_linear_pagetable(l2);
 static int
 get_page_from_l2e(
@@ -1115,9 +1110,6 @@ get_page_from_l2e(
     unsigned long mfn = l2e_get_pfn(l2e);
     int rc;
 
-    if ( !(l2e_get_flags(l2e) & _PAGE_PRESENT) )
-        return pv_l1tf_check_l2e(d, l2e) ? -ERESTART : 1;
-
     if ( unlikely((l2e_get_flags(l2e) & L2_DISALLOW_MASK)) )
     {
         gdprintk(XENLOG_WARNING, "Bad L2 flags %x\n",
@@ -1132,13 +1124,6 @@ get_page_from_l2e(
     return rc;
 }
 
-
-/*
- * get_page_from_l3e returns:
- *   1 => page not present
- *   0 => success
- *  <0 => error code
- */
 define_get_linear_pagetable(l3);
 static int
 get_page_from_l3e(
@@ -1146,9 +1131,6 @@ get_page_from_l3e(
 {
     int rc;
 
-    if ( !(l3e_get_flags(l3e) & _PAGE_PRESENT) )
-        return pv_l1tf_check_l3e(d, l3e) ? -ERESTART : 1;
-
     if ( unlikely((l3e_get_flags(l3e) & l3_disallow_mask(d))) )
     {
         gdprintk(XENLOG_WARNING, "Bad L3 flags %x\n",
@@ -1166,12 +1148,6 @@ get_page_from_l3e(
     return rc;
 }
 
-/*
- * get_page_from_l4e returns:
- *   1 => page not present
- *   0 => success
- *  <0 => error code
- */
 define_get_linear_pagetable(l4);
 static int
 get_page_from_l4e(
@@ -1179,9 +1155,6 @@ get_page_from_l4e(
 {
     int rc;
 
-    if ( !(l4e_get_flags(l4e) & _PAGE_PRESENT) )
-        return pv_l1tf_check_l4e(d, l4e) ? -ERESTART : 1;
-
     if ( unlikely((l4e_get_flags(l4e) & L4_DISALLOW_MASK)) )
     {
         gdprintk(XENLOG_WARNING, "Bad L4 flags %x\n",
@@ -1396,8 +1369,7 @@ static int alloc_l1_table(struct page_info *page)
             if ( ret )
                 goto out;
         }
-
-        switch ( ret = get_page_from_l1e(pl1e[i], d, d) )
+        else switch ( ret = get_page_from_l1e(pl1e[i], d, d) )
         {
         default:
             goto fail;
@@ -1477,6 +1449,8 @@ static int alloc_l2_table(struct page_info *page, 
unsigned long type)
 
     for ( i = page->nr_validated_ptes; i < L2_PAGETABLE_ENTRIES; i++ )
     {
+        l2_pgentry_t l2e;
+
         if ( i > page->nr_validated_ptes && hypercall_preempt_check() )
         {
             page->nr_validated_ptes = i;
@@ -1484,10 +1458,20 @@ static int alloc_l2_table(struct page_info *page, 
unsigned long type)
             break;
         }
 
-        if ( !is_guest_l2_slot(d, type, i) ||
-             (rc = get_page_from_l2e(pl2e[i], pfn, d)) > 0 )
+        if ( !is_guest_l2_slot(d, type, i) )
             continue;
 
+        l2e = pl2e[i];
+
+        if ( !(l2e_get_flags(l2e) & _PAGE_PRESENT) )
+        {
+            if ( !pv_l1tf_check_l2e(d, l2e) )
+                continue;
+            rc = -ERESTART;
+        }
+        else
+            rc = get_page_from_l2e(l2e, pfn, d);
+
         if ( unlikely(rc == -ERESTART) )
         {
             page->nr_validated_ptes = i;
@@ -1503,14 +1487,14 @@ static int alloc_l2_table(struct page_info *page, 
unsigned long type)
             break;
         }
 
-        pl2e[i] = adjust_guest_l2e(pl2e[i], d);
+        pl2e[i] = adjust_guest_l2e(l2e, d);
     }
 
-    if ( rc >= 0 && (type & PGT_pae_xen_l2) )
+    if ( !rc && (type & PGT_pae_xen_l2) )
         init_xen_pae_l2_slots(pl2e, d);
 
     unmap_domain_page(pl2e);
-    return rc > 0 ? 0 : rc;
+    return rc;
 }
 
 static int alloc_l3_table(struct page_info *page)
@@ -1536,18 +1520,26 @@ static int alloc_l3_table(struct page_info *page)
     for ( i = page->nr_validated_ptes; i < L3_PAGETABLE_ENTRIES;
           i++, partial = 0 )
     {
+        l3_pgentry_t l3e = pl3e[i];
+
         if ( is_pv_32bit_domain(d) && (i == 3) )
         {
-            if ( !(l3e_get_flags(pl3e[i]) & _PAGE_PRESENT) ||
-                 (l3e_get_flags(pl3e[i]) & l3_disallow_mask(d)) )
+            if ( !(l3e_get_flags(l3e) & _PAGE_PRESENT) ||
+                 (l3e_get_flags(l3e) & l3_disallow_mask(d)) )
                 rc = -EINVAL;
             else
                 rc = get_page_and_type_from_mfn(
-                    l3e_get_mfn(pl3e[i]),
+                    l3e_get_mfn(l3e),
                     PGT_l2_page_table | PGT_pae_xen_l2, d, partial, 1);
         }
-        else if ( (rc = get_page_from_l3e(pl3e[i], pfn, d, partial)) > 0 )
-            continue;
+        else if ( !(l3e_get_flags(l3e) & _PAGE_PRESENT) )
+        {
+            if ( !pv_l1tf_check_l3e(d, l3e) )
+                continue;
+            rc = -ERESTART;
+        }
+        else
+            rc = get_page_from_l3e(l3e, pfn, d, partial);
 
         if ( rc == -ERESTART )
         {
@@ -1563,10 +1555,10 @@ static int alloc_l3_table(struct page_info *page)
         if ( rc < 0 )
             break;
 
-        pl3e[i] = adjust_guest_l3e(pl3e[i], d);
+        pl3e[i] = adjust_guest_l3e(l3e, d);
     }
 
-    if ( rc >= 0 && !create_pae_xen_mappings(d, pl3e) )
+    if ( !rc && !create_pae_xen_mappings(d, pl3e) )
         rc = -EINVAL;
     if ( rc < 0 && rc != -ERESTART && rc != -EINTR )
     {
@@ -1583,7 +1575,7 @@ static int alloc_l3_table(struct page_info *page)
     }
 
     unmap_domain_page(pl3e);
-    return rc > 0 ? 0 : rc;
+    return rc;
 }
 
 void init_xen_pae_l2_slots(l2_pgentry_t *l2t, const struct domain *d)
@@ -1711,10 +1703,22 @@ static int alloc_l4_table(struct page_info *page)
     for ( i = page->nr_validated_ptes; i < L4_PAGETABLE_ENTRIES;
           i++, partial = 0 )
     {
-        if ( !is_guest_l4_slot(d, i) ||
-             (rc = get_page_from_l4e(pl4e[i], pfn, d, partial)) > 0 )
+        l4_pgentry_t l4e;
+
+        if ( !is_guest_l4_slot(d, i) )
             continue;
 
+        l4e = pl4e[i];
+
+        if ( !(l4e_get_flags(l4e) & _PAGE_PRESENT) )
+        {
+            if ( !pv_l1tf_check_l4e(d, l4e) )
+                continue;
+            rc = -ERESTART;
+        }
+        else
+            rc = get_page_from_l4e(l4e, pfn, d, partial);
+
         if ( rc == -ERESTART )
         {
             page->nr_validated_ptes = i;
@@ -1746,15 +1750,14 @@ static int alloc_l4_table(struct page_info *page)
             return rc;
         }
 
-        pl4e[i] = adjust_guest_l4e(pl4e[i], d);
+        pl4e[i] = adjust_guest_l4e(l4e, d);
     }
 
-    if ( rc >= 0 )
+    if ( !rc )
     {
         init_xen_l4_slots(pl4e, _mfn(pfn),
                           d, INVALID_MFN, VM_ASSIST(d, m2p_strict));
         atomic_inc(&d->arch.pv_domain.nr_l4_pages);
-        rc = 0;
     }
     unmap_domain_page(pl4e);
 
diff --git a/xen/arch/x86/pv/ro-page-fault.c b/xen/arch/x86/pv/ro-page-fault.c
index 852cd8d481..1246eeb1c5 100644
--- a/xen/arch/x86/pv/ro-page-fault.c
+++ b/xen/arch/x86/pv/ro-page-fault.c
@@ -131,10 +131,12 @@ static int ptwr_emulated_update(unsigned long addr, 
intpte_t *p_old,
     /* Check the new PTE. */
     nl1e = l1e_from_intpte(val);
 
-    if ( !(l1e_get_flags(nl1e) & _PAGE_PRESENT) && pv_l1tf_check_l1e(d, nl1e) )
-        return X86EMUL_RETRY;
-
-    switch ( ret = get_page_from_l1e(nl1e, d, d) )
+    if ( !(l1e_get_flags(nl1e) & _PAGE_PRESENT) )
+    {
+        if ( pv_l1tf_check_l1e(d, nl1e) )
+            return X86EMUL_RETRY;
+    }
+    else switch ( ret = get_page_from_l1e(nl1e, d, d) )
     {
     default:
         if ( is_pv_32bit_domain(d) && (bytes == 4) && (unaligned_addr & 4) &&
--
generated by git-patchbot for /home/xen/git/xen.git#master

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