[xen staging] x86/shadow: slightly consolidate sh_unshadow_for_p2m_change() (part III)

[patchbot@xxxxxxx]

commit 6270081c57978ff32d76d8eb11196fd217f7af2d
Author:     Jan Beulich <jbeulich@xxxxxxxx>
AuthorDate: Thu Aug 18 09:29:04 2022 +0200
Commit:     Jan Beulich <jbeulich@xxxxxxxx>
CommitDate: Thu Aug 18 09:29:04 2022 +0200

    x86/shadow: slightly consolidate sh_unshadow_for_p2m_change() (part III)
    
    In preparation for reactivating the presently dead 2M page path of the
    function, also deal with the case of replacing an L1 page table all in
    one go. Note that the prior comparing of MFNs to bypass the removal of
    shadows was insufficient (but kind of benign, for being dead code so
    far) - at the very least the R/W bit also needs considering there (to be
    on the safe side, compare the full [virtual] PTEs).
    
    While adjusting the first conditional in the loop for the use of the new
    local variable "nflags", also drop mfn_valid(): If anything we'd need to
    compare against INVALID_MFN, but that won't come out of l1e_get_mfn().
    
    Signed-off-by: Jan Beulich <jbeulich@xxxxxxxx>
    Acked-by: Tim Deegan <tim@xxxxxxx>
---
 xen/arch/x86/mm/shadow/hvm.c | 53 ++++++++++++++++++++++++++++++++------------
 1 file changed, 39 insertions(+), 14 deletions(-)

diff --git a/xen/arch/x86/mm/shadow/hvm.c b/xen/arch/x86/mm/shadow/hvm.c
index 0c670551f7..c084bc8ed7 100644
--- a/xen/arch/x86/mm/shadow/hvm.c
+++ b/xen/arch/x86/mm/shadow/hvm.c
@@ -844,40 +844,65 @@ static void cf_check sh_unshadow_for_p2m_change(
      * scheme, that's OK, but otherwise they must be unshadowed.
      */
     case 2:
-        if ( !(oflags & _PAGE_PSE) )
-            break;
-
-        ASSERT(!p2m_is_grant(p2mt));
-
         {
             unsigned int i;
             mfn_t nmfn = l1e_get_mfn(new);
-            l1_pgentry_t *npte = NULL;
+            unsigned int nflags = l1e_get_flags(new);
+            l1_pgentry_t *npte = NULL, *opte = NULL;
 
+            BUILD_BUG_ON(_PAGE_PAT != _PAGE_PSE);
+
+            if ( !(nflags & _PAGE_PRESENT) )
+                nmfn = INVALID_MFN;
             /* If we're replacing a superpage with a normal L1 page, map it */
-            if ( (l1e_get_flags(new) & _PAGE_PRESENT) &&
-                 !(l1e_get_flags(new) & _PAGE_PSE) &&
-                 mfn_valid(nmfn) )
+            else if ( !(nflags & _PAGE_PSE) )
                 npte = map_domain_page(nmfn);
+            else if ( !(mfn_x(nmfn) & (_PAGE_PSE_PAT >> PAGE_SHIFT)) )
+                nflags &= ~_PAGE_PSE;
+            else
+                nmfn = mfn_add(nmfn, -(long)(_PAGE_PSE_PAT >> PAGE_SHIFT));
+
+            /* If we're replacing a normal L1 page, map it as well. */
+            if ( !(oflags & _PAGE_PSE) )
+                opte = map_domain_page(omfn);
+            else if ( !(mfn_x(omfn) & (_PAGE_PSE_PAT >> PAGE_SHIFT)) )
+                oflags &= ~_PAGE_PSE;
+            else
+                omfn = mfn_add(omfn, -(long)(_PAGE_PSE_PAT >> PAGE_SHIFT));
 
             gfn &= ~(L1_PAGETABLE_ENTRIES - 1);
 
             for ( i = 0; i < L1_PAGETABLE_ENTRIES; i++ )
             {
-                if ( !npte ||
-                     !(l1e_get_flags(npte[i]) & _PAGE_PRESENT) ||
-                     !mfn_eq(l1e_get_mfn(npte[i]), omfn) )
+                if ( opte )
+                {
+                    oflags = l1e_get_flags(opte[i]);
+                    if ( !(oflags & _PAGE_PRESENT) )
+                        continue;
+                    omfn = l1e_get_mfn(opte[i]);
+                }
+
+                if ( npte )
+                {
+                    nflags = l1e_get_flags(npte[i]);
+                    nmfn = nflags & _PAGE_PRESENT
+                           ? l1e_get_mfn(npte[i]) : INVALID_MFN;
+                }
+
+                if ( !mfn_eq(nmfn, omfn) || nflags != oflags )
                 {
                     /* This GFN->MFN mapping has gone away */
                     sh_remove_all_shadows_and_parents(d, omfn);
                     if ( sh_remove_all_mappings(d, omfn, _gfn(gfn + i)) )
                         flush = true;
                 }
+
                 omfn = mfn_add(omfn, 1);
+                nmfn = mfn_add(nmfn, !mfn_eq(nmfn, INVALID_MFN));
             }
 
-            if ( npte )
-                unmap_domain_page(npte);
+            unmap_domain_page(opte);
+            unmap_domain_page(npte);
         }
 
         break;
--
generated by git-patchbot for /home/xen/git/xen.git#staging