paravirt: add hooks for ptep_modify_prot_start/commit

This patch adds paravirt-ops hooks in pv_mmu_ops for ptep_modify_prot_start and
ptep_modify_prot_commit.  This allows the hypervisor-specific backends to
implement these in some more efficient way.
Signed-off-by: Jeremy Fitzhardinge <jeremy.fitzhardinge@citrix.com>
Acked-by: Linus Torvalds <torvalds@linux-foundation.org>
Acked-by: Hugh Dickins <hugh@veritas.com>
Signed-off-by: Ingo Molnar <mingo@elte.hu>

arch/x86/kernel/paravirt.c

@@ -380,6 +380,9 @@ struct pv_mmu_ops pv_mmu_ops = {
 	.pte_update = paravirt_nop,
 	.pte_update_defer = paravirt_nop,
 
+	.ptep_modify_prot_start = __ptep_modify_prot_start,
+	.ptep_modify_prot_commit = __ptep_modify_prot_commit,
+
 #ifdef CONFIG_HIGHPTE
 	.kmap_atomic_pte = kmap_atomic,
 #endif

arch/x86/xen/enlighten.c

@@ -1138,6 +1138,9 @@ static const struct pv_mmu_ops xen_mmu_ops __initdata = {
 	.set_pte_at = xen_set_pte_at,
 	.set_pmd = xen_set_pmd_hyper,
 
+	.ptep_modify_prot_start = __ptep_modify_prot_start,
+	.ptep_modify_prot_commit = __ptep_modify_prot_commit,
+
 	.pte_val = xen_pte_val,
 	.pte_flags = native_pte_val,
 	.pgd_val = xen_pgd_val,

include/asm-x86/paravirt.h

@@ -238,6 +238,11 @@ struct pv_mmu_ops {
 	void (*pte_update_defer)(struct mm_struct *mm,
 				 unsigned long addr, pte_t *ptep);
 
+	pte_t (*ptep_modify_prot_start)(struct mm_struct *mm, unsigned long addr,
+					pte_t *ptep);
+	void (*ptep_modify_prot_commit)(struct mm_struct *mm, unsigned long addr,
+					pte_t *ptep, pte_t pte);
+
 	pteval_t (*pte_val)(pte_t);
 	pteval_t (*pte_flags)(pte_t);
 	pte_t (*make_pte)(pteval_t pte);
@@ -1039,6 +1044,29 @@ static inline pgdval_t pgd_val(pgd_t pgd)
 	return ret;
 }
 
+#define  __HAVE_ARCH_PTEP_MODIFY_PROT_TRANSACTION
+static inline pte_t ptep_modify_prot_start(struct mm_struct *mm, unsigned long addr,
+					   pte_t *ptep)
+{
+	pteval_t ret;
+
+	ret = PVOP_CALL3(pteval_t, pv_mmu_ops.ptep_modify_prot_start,
+			 mm, addr, ptep);
+
+	return (pte_t) { .pte = ret };
+}
+
+static inline void ptep_modify_prot_commit(struct mm_struct *mm, unsigned long addr,
+					   pte_t *ptep, pte_t pte)
+{
+	if (sizeof(pteval_t) > sizeof(long))
+		/* 5 arg words */
+		pv_mmu_ops.ptep_modify_prot_commit(mm, addr, ptep, pte);
+	else
+		PVOP_VCALL4(pv_mmu_ops.ptep_modify_prot_commit,
+			    mm, addr, ptep, pte.pte);
+}
+
 static inline void set_pte(pte_t *ptep, pte_t pte)
 {
 	if (sizeof(pteval_t) > sizeof(long))