x86: Call HVMOP_pagetable_dying on exit_mmap.

When a pagetable is about to be destroyed, we notify Xen so that the
hypervisor can clear the related shadow pagetable.
Signed-off-by: Stefano Stabellini <stefano.stabellini@eu.citrix.com>
Signed-off-by: Jeremy Fitzhardinge <jeremy.fitzhardinge@citrix.com>

arch/x86/xen/enlighten.c

@@ -1318,6 +1318,7 @@ static void __init xen_hvm_guest_init(void)
 	have_vcpu_info_placement = 0;
 	x86_init.irqs.intr_init = xen_init_IRQ;
 	xen_hvm_init_time_ops();
+	xen_hvm_init_mmu_ops();
 }
 
 static bool __init xen_hvm_platform(void)

arch/x86/xen/mmu.c

@@ -58,6 +58,7 @@
 
 #include <xen/page.h>
 #include <xen/interface/xen.h>
+#include <xen/interface/hvm/hvm_op.h>
 #include <xen/interface/version.h>
 #include <xen/hvc-console.h>
 
@@ -1941,6 +1942,38 @@ void __init xen_init_mmu_ops(void)
 	pv_mmu_ops = xen_mmu_ops;
 }
 
+static void xen_hvm_exit_mmap(struct mm_struct *mm)
+{
+	struct xen_hvm_pagetable_dying a;
+	int rc;
+
+	a.domid = DOMID_SELF;
+	a.gpa = __pa(mm->pgd);
+	rc = HYPERVISOR_hvm_op(HVMOP_pagetable_dying, &a);
+	WARN_ON_ONCE(rc < 0);
+}
+
+static int is_pagetable_dying_supported(void)
+{
+	struct xen_hvm_pagetable_dying a;
+	int rc = 0;
+
+	a.domid = DOMID_SELF;
+	a.gpa = 0x00;
+	rc = HYPERVISOR_hvm_op(HVMOP_pagetable_dying, &a);
+	if (rc < 0) {
+		printk(KERN_DEBUG "HVMOP_pagetable_dying not supported\n");
+		return 0;
+	}
+	return 1;
+}
+
+void __init xen_hvm_init_mmu_ops(void)
+{
+	if (is_pagetable_dying_supported())
+		pv_mmu_ops.exit_mmap = xen_hvm_exit_mmap;
+}
+
 #ifdef CONFIG_XEN_DEBUG_FS
 
 static struct dentry *d_mmu_debug;

arch/x86/xen/mmu.h

@@ -60,4 +60,5 @@ void  xen_ptep_modify_prot_commit(struct mm_struct *mm, unsigned long addr,
 unsigned long xen_read_cr2_direct(void);
 
 extern void xen_init_mmu_ops(void);
+extern void xen_hvm_init_mmu_ops(void);
 #endif	/* _XEN_MMU_H */

include/xen/interface/hvm/hvm_op.h

@@ -32,4 +32,15 @@ struct xen_hvm_param {
 };
 DEFINE_GUEST_HANDLE_STRUCT(xen_hvm_param);
 
+/* Hint from PV drivers for pagetable destruction. */
+#define HVMOP_pagetable_dying       9
+struct xen_hvm_pagetable_dying {
+    /* Domain with a pagetable about to be destroyed. */
+    domid_t  domid;
+    /* guest physical address of the toplevel pagetable dying */
+    aligned_u64 gpa;
+};
+typedef struct xen_hvm_pagetable_dying xen_hvm_pagetable_dying_t;
+DEFINE_GUEST_HANDLE_STRUCT(xen_hvm_pagetable_dying_t);
+ 
 #endif /* __XEN_PUBLIC_HVM_HVM_OP_H__ */