[xen master] x86/PV: make post-migration page state consistent

[patchbot@xxxxxxx]

commit 0a87e677f4f4527c439fa12a6d7fa44a28e43cb3
Author:     Jan Beulich <jbeulich@xxxxxxxx>
AuthorDate: Fri Apr 9 09:15:38 2021 +0200
Commit:     Jan Beulich <jbeulich@xxxxxxxx>
CommitDate: Fri Apr 9 09:15:38 2021 +0200

    x86/PV: make post-migration page state consistent
    
    When a page table page gets de-validated, its type reference count drops
    to zero (and PGT_validated gets cleared), but its type remains intact.
    XEN_DOMCTL_getpageframeinfo3, therefore, so far reported prior usage for
    such pages. An intermediate write to such a page via e.g.
    MMU_NORMAL_PT_UPDATE, however, would transition the page's type to
    PGT_writable_page, thus altering what XEN_DOMCTL_getpageframeinfo3 would
    return. In libxc the decision which pages to normalize / localize
    depends solely on the type returned from the domctl. As a result without
    further precautions the guest won't be able to tell whether such a page
    has had its (apparent) PTE entries transitioned to the new MFNs.
    
    Add a check of PGT_validated, thus consistently avoiding normalization /
    localization in the tool stack.
    
    Also use XEN_DOMCTL_PFINFO_NOTAB in the variable's initializer instead
    open coding it.
    
    Signed-off-by: Jan Beulich <jbeulich@xxxxxxxx>
    Acked-by: Roger Pau Monné <roger.pau@xxxxxxxxxx>
---
 xen/arch/x86/domctl.c | 4 +++-
 1 file changed, 3 insertions(+), 1 deletion(-)

diff --git a/xen/arch/x86/domctl.c b/xen/arch/x86/domctl.c
index b129d2cc2f..2aea5b6e9a 100644
--- a/xen/arch/x86/domctl.c
+++ b/xen/arch/x86/domctl.c
@@ -262,7 +262,7 @@ long arch_do_domctl(
 
         for ( i = 0; i < num; ++i )
         {
-            unsigned long gfn = 0, type = 0;
+            unsigned long gfn = 0, type = XEN_DOMCTL_PFINFO_NOTAB;
             struct page_info *page;
             p2m_type_t t;
 
@@ -302,6 +302,8 @@ long arch_do_domctl(
 
                 if ( page->u.inuse.type_info & PGT_pinned )
                     type |= XEN_DOMCTL_PFINFO_LPINTAB;
+                else if ( !(page->u.inuse.type_info & PGT_validated) )
+                    type = XEN_DOMCTL_PFINFO_NOTAB;
 
                 if ( page->count_info & PGC_broken )
                     type = XEN_DOMCTL_PFINFO_BROKEN;
--
generated by git-patchbot for /home/xen/git/xen.git#master