[Xen-devel] [PATCH v8 07/11] x86/mm: add an extra command to HYPERVISOR_mmu_update...

[Paul Durrant <paul.durrant@xxxxxxxxxx>]

...to allow the calling domain to prevent translation of specified l1e
value.

Despite what the comment in public/xen.h might imply, specifying a
command value of MMU_NORMAL_PT_UPDATE will not simply update an l1e with
the specified value. Instead, mod_l1_entry() tests whether foreign_dom
has PG_translate set in its paging mode and, if it does, assumes that the
the pfn value in the l1e is a gfn rather than an mfn.

To allow PV tools domain to map mfn values from a previously issued
HYPERVISOR_memory_op:XENMEM_acquire_resource, there needs to be a way
to tell HYPERVISOR_mmu_update that the specific l1e value does not
require translation regardless of the paging mode of foreign_dom. This
patch therefore defines a new command value, MMU_PT_UPDATE_NO_TRANSLATE,
which has the same semantics as MMU_NORMAL_PT_UPDATE except that the
paging mode of foreign_dom is ignored and the l1e value is used verbatim.

Signed-off-by: Paul Durrant <paul.durrant@xxxxxxxxxx>
---
Cc: Jan Beulich <jbeulich@xxxxxxxx>
Cc: Andrew Cooper <andrew.cooper3@xxxxxxxxxx>
Cc: George Dunlap <George.Dunlap@xxxxxxxxxxxxx>
Cc: Ian Jackson <ian.jackson@xxxxxxxxxxxxx>
Cc: Konrad Rzeszutek Wilk <konrad.wilk@xxxxxxxxxx>
Cc: Stefano Stabellini <sstabellini@xxxxxxxxxx>
Cc: Tim Deegan <tim@xxxxxxx>
Cc: Wei Liu <wei.liu2@xxxxxxxxxx>

v8:
 - New in this version, replacing "allow a privileged PV domain to map
   guest mfns".
---
 xen/arch/x86/mm.c        | 17 ++++++++++-------
 xen/include/public/xen.h | 12 +++++++++---
 2 files changed, 19 insertions(+), 10 deletions(-)

diff --git a/xen/arch/x86/mm.c b/xen/arch/x86/mm.c
index c9bc4a4e92..d63ab049f9 100644
--- a/xen/arch/x86/mm.c
+++ b/xen/arch/x86/mm.c
@@ -1619,9 +1619,10 @@ void page_unlock(struct page_info *page)
 
 /* Update the L1 entry at pl1e to new value nl1e. */
 static int mod_l1_entry(l1_pgentry_t *pl1e, l1_pgentry_t nl1e,
-                        unsigned long gl1mfn, int preserve_ad,
+                        unsigned long gl1mfn, int cmd,
                         struct vcpu *pt_vcpu, struct domain *pg_dom)
 {
+    bool preserve_ad = (cmd == MMU_PT_UPDATE_PRESERVE_AD);
     l1_pgentry_t ol1e;
     struct domain *pt_dom = pt_vcpu->domain;
     int rc = 0;
@@ -1643,7 +1644,8 @@ static int mod_l1_entry(l1_pgentry_t *pl1e, l1_pgentry_t 
nl1e,
             return -EINVAL;
         }
 
-        if ( paging_mode_translate(pg_dom) )
+        if ( cmd != MMU_PT_UPDATE_NO_TRANSLATE &&
+             paging_mode_translate(pg_dom) )
         {
             page = get_page_from_gfn(pg_dom, l1e_get_pfn(nl1e), NULL, 
P2M_ALLOC);
             if ( !page )
@@ -3258,6 +3260,7 @@ long do_mmu_update(
              */
         case MMU_NORMAL_PT_UPDATE:
         case MMU_PT_UPDATE_PRESERVE_AD:
+        case MMU_PT_UPDATE_NO_TRANSLATE:
         {
             p2m_type_t p2mt;
 
@@ -3323,7 +3326,8 @@ long do_mmu_update(
                     p2m_query_t q = (l1e_get_flags(l1e) & _PAGE_RW) ?
                                         P2M_UNSHARE : P2M_ALLOC;
 
-                    if ( paging_mode_translate(pg_owner) )
+                    if ( cmd != MMU_PT_UPDATE_NO_TRANSLATE &&
+                         paging_mode_translate(pg_owner) )
                         target = get_page_from_gfn(pg_owner, l1e_get_pfn(l1e),
                                                    &l1e_p2mt, q);
 
@@ -3350,9 +3354,7 @@ long do_mmu_update(
                         break;
                     }
 
-                    rc = mod_l1_entry(va, l1e, mfn,
-                                      cmd == MMU_PT_UPDATE_PRESERVE_AD, v,
-                                      pg_owner);
+                    rc = mod_l1_entry(va, l1e, mfn, cmd, v, pg_owner);
                     if ( target )
                         put_page(target);
                 }
@@ -3630,7 +3632,8 @@ static int __do_update_va_mapping(
         goto out;
     }
 
-    rc = mod_l1_entry(pl1e, val, mfn_x(gl1mfn), 0, v, pg_owner);
+    rc = mod_l1_entry(pl1e, val, mfn_x(gl1mfn), MMU_NORMAL_PT_UPDATE, v,
+                      pg_owner);
 
     page_unlock(gl1pg);
     put_page(gl1pg);
diff --git a/xen/include/public/xen.h b/xen/include/public/xen.h
index 2ac6b1e24d..d2014a39eb 100644
--- a/xen/include/public/xen.h
+++ b/xen/include/public/xen.h
@@ -268,6 +268,10 @@ DEFINE_XEN_GUEST_HANDLE(xen_ulong_t);
  * As MMU_NORMAL_PT_UPDATE above, but A/D bits currently in the PTE are ORed
  * with those in @val.
  *
+ * ptr[1:0] == MMU_PT_UPDATE_NO_TRANSLATE:
+ * As MMU_NORMAL_PT_UPDATE above, but @val is not translated though FD
+ * page tables.
+ *
  * @val is usually the machine frame number along with some attributes.
  * The attributes by default follow the architecture defined bits. Meaning that
  * if this is a X86_64 machine and four page table layout is used, the layout
@@ -334,9 +338,11 @@ DEFINE_XEN_GUEST_HANDLE(xen_ulong_t);
  *
  * PAT (bit 7 on) --> PWT (bit 3 on) and clear bit 7.
  */
-#define MMU_NORMAL_PT_UPDATE      0 /* checked '*ptr = val'. ptr is MA.      */
-#define MMU_MACHPHYS_UPDATE       1 /* ptr = MA of frame to modify entry for */
-#define MMU_PT_UPDATE_PRESERVE_AD 2 /* atomically: *ptr = val | (*ptr&(A|D)) */
+#define MMU_NORMAL_PT_UPDATE       0 /* checked '*ptr = val'. ptr is MA.      
*/
+#define MMU_MACHPHYS_UPDATE        1 /* ptr = MA of frame to modify entry for 
*/
+#define MMU_PT_UPDATE_PRESERVE_AD  2 /* atomically: *ptr = val | (*ptr&(A|D)) 
*/
+#define MMU_PT_UPDATE_NO_TRANSLATE 3 /* checked '*ptr = val'. prt is MA.      
*/
+                                     /* val never translated.                  
*/
 
 /*
  * MMU EXTENDED OPERATIONS
-- 
2.11.0


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