[xen stable-4.14] x86/paging: restrict physical address width reported to guests

[patchbot@xxxxxxx]

commit 81e3fd1f3cacda220e4d46bb01f9c1b554ed8401
Author:     Jan Beulich <jbeulich@xxxxxxxx>
AuthorDate: Fri Nov 19 09:38:42 2021 +0100
Commit:     Jan Beulich <jbeulich@xxxxxxxx>
CommitDate: Fri Nov 19 09:38:42 2021 +0100

    x86/paging: restrict physical address width reported to guests
    
    Modern hardware may report more than 48 bits of physical address width.
    For paging-external guests our P2M implementation does not cope with
    larger values. Telling the guest of more available bits means misleading
    it into perhaps trying to actually put some page there (like was e.g.
    intermediately done in OVMF for the shared info page).
    
    While there also convert the PV check to a paging-external one (which in
    our current code base are synonyms of one another anyway).
    
    Fixes: 5dbd60e16a1f ("x86/shadow: Correct guest behaviour when creating 
PTEs above maxphysaddr")
    Signed-off-by: Jan Beulich <jbeulich@xxxxxxxx>
    Reviewed-by: Roger Pau Monné <roger.pau@xxxxxxxxxx>
    master commit: b7635526acffbe4ad8ad16fd92812c57742e54c2
    master date: 2021-10-19 10:08:30 +0200
---
 xen/include/asm-x86/paging.h | 15 +++++++++++----
 1 file changed, 11 insertions(+), 4 deletions(-)

diff --git a/xen/include/asm-x86/paging.h b/xen/include/asm-x86/paging.h
index f53575f3d9..abb9a7e75c 100644
--- a/xen/include/asm-x86/paging.h
+++ b/xen/include/asm-x86/paging.h
@@ -391,11 +391,18 @@ static always_inline unsigned int 
paging_max_paddr_bits(const struct domain *d)
 {
     unsigned int bits = paging_mode_hap(d) ? hap_paddr_bits : paddr_bits;
 
-    if ( !IS_ENABLED(CONFIG_BIGMEM) && paging_mode_shadow(d) &&
-         !is_pv_domain(d) )
+    if ( paging_mode_external(d) )
     {
-        /* Shadowed superpages store GFNs in 32-bit page_info fields. */
-        bits = min(bits, 32U + PAGE_SHIFT);
+        if ( !IS_ENABLED(CONFIG_BIGMEM) && paging_mode_shadow(d) )
+        {
+            /* Shadowed superpages store GFNs in 32-bit page_info fields. */
+            bits = min(bits, 32U + PAGE_SHIFT);
+        }
+        else
+        {
+            /* Both p2m-ept and p2m-pt only support 4-level page tables. */
+            bits = min(bits, 48U);
+        }
     }
 
     return bits;
--
generated by git-patchbot for /home/xen/git/xen.git#stable-4.14