[xen staging] x86/altp2m: p2m_altp2m_get_or_propagate() should honor present page order

[patchbot@xxxxxxx]

commit ced5685208f4525edc3aa86f41eeaee5ccc9fe31
Author:     Jan Beulich <jbeulich@xxxxxxxx>
AuthorDate: Thu Jan 6 16:12:39 2022 +0100
Commit:     Jan Beulich <jbeulich@xxxxxxxx>
CommitDate: Thu Jan 6 16:12:39 2022 +0100

    x86/altp2m: p2m_altp2m_get_or_propagate() should honor present page order
    
    Prior to XSA-304 the only caller merely happened to not use any further
    the order value that it passes into the function. Already then this was
    a latent issue: The function really should, in the "get" case, hand back
    the order the underlying mapping actually uses (or actually the smaller
    of the two), such that (going forward) there wouldn't be any action on
    unrelated mappings (in particular ones which did already diverge from
    the host P2M).
    
    Similarly in the "propagate" case only the smaller of the two orders
    should actually get used for creating the new entry, again to avoid
    altering mappings which did already diverge from the host P2M.
    
    Signed-off-by: Jan Beulich <jbeulich@xxxxxxxx>
    Reviewed-by: Tamas K Lengyel <tamas@xxxxxxxxxxxxx>
---
 xen/arch/x86/hvm/hvm.c         |  2 +-
 xen/arch/x86/include/asm/p2m.h |  2 +-
 xen/arch/x86/mm/p2m.c          | 14 ++++++++++----
 3 files changed, 12 insertions(+), 6 deletions(-)

diff --git a/xen/arch/x86/hvm/hvm.c b/xen/arch/x86/hvm/hvm.c
index 350dc396e3..d233550ae4 100644
--- a/xen/arch/x86/hvm/hvm.c
+++ b/xen/arch/x86/hvm/hvm.c
@@ -1832,7 +1832,7 @@ int hvm_hap_nested_page_fault(paddr_t gpa, unsigned long 
gla,
          * altp2m.
          */
         if ( p2m_altp2m_get_or_propagate(p2m, gfn, &mfn, &p2mt,
-                                         &p2ma, page_order) )
+                                         &p2ma, &page_order) )
         {
             /* Entry was copied from host -- retry fault */
             rc = 1;
diff --git a/xen/arch/x86/include/asm/p2m.h b/xen/arch/x86/include/asm/p2m.h
index 357a808748..6e2206874d 100644
--- a/xen/arch/x86/include/asm/p2m.h
+++ b/xen/arch/x86/include/asm/p2m.h
@@ -852,7 +852,7 @@ void p2m_flush_altp2m(struct domain *d);
 /* Alternate p2m paging */
 bool p2m_altp2m_get_or_propagate(struct p2m_domain *ap2m, unsigned long gfn_l,
                                  mfn_t *mfn, p2m_type_t *p2mt,
-                                 p2m_access_t *p2ma, unsigned int page_order);
+                                 p2m_access_t *p2ma, unsigned int *page_order);
 
 /* Make a specific alternate p2m valid */
 int p2m_init_altp2m_by_id(struct domain *d, unsigned int idx);
diff --git a/xen/arch/x86/mm/p2m.c b/xen/arch/x86/mm/p2m.c
index 1d5a87a969..98c8201f92 100644
--- a/xen/arch/x86/mm/p2m.c
+++ b/xen/arch/x86/mm/p2m.c
@@ -2198,10 +2198,11 @@ bool_t p2m_switch_vcpu_altp2m_by_id(struct vcpu *v, 
unsigned int idx)
  */
 bool p2m_altp2m_get_or_propagate(struct p2m_domain *ap2m, unsigned long gfn_l,
                                  mfn_t *mfn, p2m_type_t *p2mt,
-                                 p2m_access_t *p2ma, unsigned int page_order)
+                                 p2m_access_t *p2ma, unsigned int *page_order)
 {
     p2m_type_t ap2mt;
     p2m_access_t ap2ma;
+    unsigned int cur_order;
     unsigned long mask;
     gfn_t gfn;
     mfn_t amfn;
@@ -2214,7 +2215,10 @@ bool p2m_altp2m_get_or_propagate(struct p2m_domain 
*ap2m, unsigned long gfn_l,
      */
     p2m_lock(ap2m);
 
-    amfn = get_gfn_type_access(ap2m, gfn_l, &ap2mt, &ap2ma, 0, NULL);
+    amfn = get_gfn_type_access(ap2m, gfn_l, &ap2mt, &ap2ma, 0, &cur_order);
+
+    if ( cur_order > *page_order )
+        cur_order = *page_order;
 
     if ( !mfn_eq(amfn, INVALID_MFN) )
     {
@@ -2222,6 +2226,7 @@ bool p2m_altp2m_get_or_propagate(struct p2m_domain *ap2m, 
unsigned long gfn_l,
         *mfn  = amfn;
         *p2mt = ap2mt;
         *p2ma = ap2ma;
+        *page_order = cur_order;
         return false;
     }
 
@@ -2229,6 +2234,7 @@ bool p2m_altp2m_get_or_propagate(struct p2m_domain *ap2m, 
unsigned long gfn_l,
     if ( mfn_eq(*mfn, INVALID_MFN) )
     {
         p2m_unlock(ap2m);
+        *page_order = cur_order;
         return false;
     }
 
@@ -2237,11 +2243,11 @@ bool p2m_altp2m_get_or_propagate(struct p2m_domain 
*ap2m, unsigned long gfn_l,
      * to the start of the superpage.  NB that we repupose `amfn`
      * here.
      */
-    mask = ~((1UL << page_order) - 1);
+    mask = ~((1UL << cur_order) - 1);
     amfn = _mfn(mfn_x(*mfn) & mask);
     gfn = _gfn(gfn_l & mask);
 
-    rc = p2m_set_entry(ap2m, gfn, amfn, page_order, *p2mt, *p2ma);
+    rc = p2m_set_entry(ap2m, gfn, amfn, cur_order, *p2mt, *p2ma);
     p2m_unlock(ap2m);
 
     if ( rc )
--
generated by git-patchbot for /home/xen/git/xen.git#staging