[RFC][PATCH 2/9] x86/mm/pae: Make pmd_t similar to pte_t

[Peter Zijlstra <peterz@infradead.org>]

Instead of mucking about with at least 2 different ways of fudging
it, do the same thing we do for pte_t.

Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
---
 arch/x86/include/asm/pgtable-3level.h       |   42 +++++++++-------------------
 arch/x86/include/asm/pgtable-3level_types.h |    7 ++++
 arch/x86/include/asm/pgtable_64_types.h     |    1 
 arch/x86/include/asm/pgtable_types.h        |    4 --
 4 files changed, 23 insertions(+), 31 deletions(-)

--- a/arch/x86/include/asm/pgtable-3level.h
+++ b/arch/x86/include/asm/pgtable-3level.h
@@ -87,7 +87,7 @@ static inline pmd_t pmd_read_atomic(pmd_
 		ret |= ((pmdval_t)*(tmp + 1)) << 32;
 	}
 
-	return (pmd_t) { ret };
+	return (pmd_t) { .pmd = ret };
 }
 
 static inline void native_set_pte_atomic(pte_t *ptep, pte_t pte)
@@ -121,12 +121,11 @@ static inline void native_pte_clear(stru
 	ptep->pte_high = 0;
 }
 
-static inline void native_pmd_clear(pmd_t *pmd)
+static inline void native_pmd_clear(pmd_t *pmdp)
 {
-	u32 *tmp = (u32 *)pmd;
-	*tmp = 0;
+	pmdp->pmd_low = 0;
 	smp_wmb();
-	*(tmp + 1) = 0;
+	pmdp->pmd_high = 0;
 }
 
 static inline void native_pud_clear(pud_t *pudp)
@@ -162,25 +161,17 @@ static inline pte_t native_ptep_get_and_
 #define native_ptep_get_and_clear(xp) native_local_ptep_get_and_clear(xp)
 #endif
 
-union split_pmd {
-	struct {
-		u32 pmd_low;
-		u32 pmd_high;
-	};
-	pmd_t pmd;
-};
-
 #ifdef CONFIG_SMP
 static inline pmd_t native_pmdp_get_and_clear(pmd_t *pmdp)
 {
-	union split_pmd res, *orig = (union split_pmd *)pmdp;
+	pmd_t res;
 
 	/* xchg acts as a barrier before setting of the high bits */
-	res.pmd_low = xchg(&orig->pmd_low, 0);
-	res.pmd_high = orig->pmd_high;
-	orig->pmd_high = 0;
+	res.pmd_low = xchg(&pmdp->pmd_low, 0);
+	res.pmd_high = READ_ONCE(pmdp->pmd_high);
+	WRITE_ONCE(pmdp->pmd_high, 0);
 
-	return res.pmd;
+	return res;
 }
 #else
 #define native_pmdp_get_and_clear(xp) native_local_pmdp_get_and_clear(xp)
@@ -199,17 +190,12 @@ static inline pmd_t pmdp_establish(struc
 	 * anybody.
 	 */
 	if (!(pmd_val(pmd) & _PAGE_PRESENT)) {
-		union split_pmd old, new, *ptr;
-
-		ptr = (union split_pmd *)pmdp;
-
-		new.pmd = pmd;
-
 		/* xchg acts as a barrier before setting of the high bits */
-		old.pmd_low = xchg(&ptr->pmd_low, new.pmd_low);
-		old.pmd_high = ptr->pmd_high;
-		ptr->pmd_high = new.pmd_high;
-		return old.pmd;
+		old.pmd_low = xchg(&pmdp->pmd_low, pmd.pmd_low);
+		old.pmd_high = READ_ONCE(pmdp->pmd_high);
+		WRITE_ONCE(pmdp->pmd_high, pmd.pmd_high);
+
+		return old;
 	}
 
 	do {
--- a/arch/x86/include/asm/pgtable-3level_types.h
+++ b/arch/x86/include/asm/pgtable-3level_types.h
@@ -18,6 +18,13 @@ typedef union {
 	};
 	pteval_t pte;
 } pte_t;
+
+typedef union {
+	struct {
+		unsigned long pmd_low, pmd_high;
+	};
+	pmdval_t pmd;
+} pmd_t;
 #endif	/* !__ASSEMBLY__ */
 
 #define SHARED_KERNEL_PMD	(!static_cpu_has(X86_FEATURE_PTI))
--- a/arch/x86/include/asm/pgtable_64_types.h
+++ b/arch/x86/include/asm/pgtable_64_types.h
@@ -19,6 +19,7 @@ typedef unsigned long	pgdval_t;
 typedef unsigned long	pgprotval_t;
 
 typedef struct { pteval_t pte; } pte_t;
+typedef struct { pmdval_t pmd; } pmd_t;
 
 #ifdef CONFIG_X86_5LEVEL
 extern unsigned int __pgtable_l5_enabled;
--- a/arch/x86/include/asm/pgtable_types.h
+++ b/arch/x86/include/asm/pgtable_types.h
@@ -381,11 +381,9 @@ static inline pudval_t native_pud_val(pu
 #endif
 
 #if CONFIG_PGTABLE_LEVELS > 2
-typedef struct { pmdval_t pmd; } pmd_t;
-
 static inline pmd_t native_make_pmd(pmdval_t val)
 {
-	return (pmd_t) { val };
+	return (pmd_t) { .pmd = val };
 }
 
 static inline pmdval_t native_pmd_val(pmd_t pmd)