5 files changed, 45 insertions, 5 deletions

diff --git a/arch/x86/xen/enlighten.c b/arch/x86/xen/enlighten.c
index 0b7553cbc529..bd74229081c3 100644
--- a/arch/x86/xen/enlighten.c
+++ b/arch/x86/xen/enlighten.c
@@ -168,7 +168,9 @@ static void __init xen_banner(void)
 {
         printk(KERN_INFO "Booting paravirtualized kernel on %s\n",
                pv_info.name);
-        printk(KERN_INFO "Hypervisor signature: %s\n", xen_start_info->magic);
+        printk(KERN_INFO "Hypervisor signature: %s%s\n",
+               xen_start_info->magic,
+               xen_feature(XENFEAT_mmu_pt_update_preserve_ad) ? " (preserve-AD)" : "");
 }
 
 static void xen_cpuid(unsigned int *ax, unsigned int *bx,
@@ -1243,6 +1245,8 @@ asmlinkage void __init xen_start_kernel(void)
 
         BUG_ON(memcmp(xen_start_info->magic, "xen-3", 5) != 0);
 
+        xen_setup_features();
+
         /* Install Xen paravirt ops */
         pv_info = xen_info;
         pv_init_ops = xen_init_ops;
@@ -1252,14 +1256,17 @@ asmlinkage void __init xen_start_kernel(void)
         pv_apic_ops = xen_apic_ops;
         pv_mmu_ops = xen_mmu_ops;
 
+        if (xen_feature(XENFEAT_mmu_pt_update_preserve_ad)) {
+                pv_mmu_ops.ptep_modify_prot_start = xen_ptep_modify_prot_start;
+                pv_mmu_ops.ptep_modify_prot_commit = xen_ptep_modify_prot_commit;
+        }
+
         machine_ops = xen_machine_ops;
 
 #ifdef CONFIG_SMP
         smp_ops = xen_smp_ops;
 #endif
 
-        xen_setup_features();
-
         /* Get mfn list */
         if (!xen_feature(XENFEAT_auto_translated_physmap))
                 xen_build_dynamic_phys_to_machine();
diff --git a/arch/x86/xen/mmu.c b/arch/x86/xen/mmu.c
index 8132aa8c5d49..846dad7d54a5 100644
--- a/arch/x86/xen/mmu.c
+++ b/arch/x86/xen/mmu.c
@@ -323,6 +323,27 @@ out:
                 preempt_enable();
 }
 
+pte_t xen_ptep_modify_prot_start(struct mm_struct *mm, unsigned long addr, pte_t *ptep)
+{
+        /* Just return the pte as-is.  We preserve the bits on commit */
+        return *ptep;
+}
+
+void xen_ptep_modify_prot_commit(struct mm_struct *mm, unsigned long addr,
+                                 pte_t *ptep, pte_t pte)
+{
+        struct multicall_space mcs;
+        struct mmu_update *u;
+
+        mcs = xen_mc_entry(sizeof(*u));
+        u = mcs.args;
+        u->ptr = virt_to_machine(ptep).maddr | MMU_PT_UPDATE_PRESERVE_AD;
+        u->val = pte_val_ma(pte);
+        MULTI_mmu_update(mcs.mc, u, 1, NULL, DOMID_SELF);
+
+        xen_mc_issue(PARAVIRT_LAZY_MMU);
+}
+
 /* Assume pteval_t is equivalent to all the other *val_t types. */
 static pteval_t pte_mfn_to_pfn(pteval_t val)
 {
diff --git a/arch/x86/xen/mmu.h b/arch/x86/xen/mmu.h
index e3dd09e25c63..297bf9f5b8bc 100644
--- a/arch/x86/xen/mmu.h
+++ b/arch/x86/xen/mmu.h
@@ -52,4 +52,8 @@ void xen_set_pud_hyper(pud_t *ptr, pud_t val);
 void xen_pte_clear(struct mm_struct *mm, unsigned long addr, pte_t *ptep);
 void xen_pmd_clear(pmd_t *pmdp);
 
+pte_t xen_ptep_modify_prot_start(struct mm_struct *mm, unsigned long addr, pte_t *ptep);
+void  xen_ptep_modify_prot_commit(struct mm_struct *mm, unsigned long addr,
+                                  pte_t *ptep, pte_t pte);
+
 #endif  /* _XEN_MMU_H */
diff --git a/include/xen/interface/features.h b/include/xen/interface/features.h
index d73228d16488..f51b6413b054 100644
--- a/include/xen/interface/features.h
+++ b/include/xen/interface/features.h
@@ -38,6 +38,9 @@
  */
 #define XENFEAT_pae_pgdir_above_4gb        4
 
+/* x86: Does this Xen host support the MMU_PT_UPDATE_PRESERVE_AD hypercall? */
+#define XENFEAT_mmu_pt_update_preserve_ad  5
+
 #define XENFEAT_NR_SUBMAPS 1
 
 #endif /* __XEN_PUBLIC_FEATURES_H__ */
diff --git a/include/xen/interface/xen.h b/include/xen/interface/xen.h
index 819a0331cda9..2befa3e2f1bc 100644
--- a/include/xen/interface/xen.h
+++ b/include/xen/interface/xen.h
@@ -114,9 +114,14 @@
  * ptr[:2]  -- Machine address within the frame whose mapping to modify.
  *             The frame must belong to the FD, if one is specified.
  * val      -- Value to write into the mapping entry.
+ *
+ * ptr[1:0] == MMU_PT_UPDATE_PRESERVE_AD:
+ * As MMU_NORMAL_PT_UPDATE above, but A/D bits currently in the PTE are ORed
+ * with those in @val.
  */
-#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_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)) */
 
 /*
  * MMU EXTENDED OPERATIONS