[PATCH 12/13] x86/mm/pae: Get rid of set_64bit()

Peter Zijlstra
2022-10-22T11:49:28Z

Recognise that set_64bit() is a special case of our previously
introduced pxx_xchg64(), so use that and get rid of set_64bit().

Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
---
arch/x86/include/asm/cmpxchg_32.h | 28 ----------------------------
arch/x86/include/asm/pgtable-3level.h | 23 ++++++++++++-----------
2 files changed, 12 insertions(+), 39 deletions(-)

--- a/arch/x86/include/asm/cmpxchg_32.h
+++ b/arch/x86/include/asm/cmpxchg_32.h
@@ -7,34 +7,6 @@
* you need to test for the feature in boot_cpu_data.
*/

-/*
- * CMPXCHG8B only writes to the target if we had the previous
- * value in registers, otherwise it acts as a read and gives us the
- * "new previous" value. That is why there is a loop. Preloading
- * EDX:EAX is a performance optimization: in the common case it means
- * we need only one locked operation.
- *
- * A SIMD/3DNOW!/MMX/FPU 64-bit store here would require at the very
- * least an FPU save and/or %cr0.ts manipulation.
- *
- * cmpxchg8b must be used with the lock prefix here to allow the
- * instruction to be executed atomically. We need to have the reader
- * side to see the coherent 64bit value.
- */
-static inline void set_64bit(volatile u64 *ptr, u64 value)
-{
- u32 low = value;
- u32 high = value >> 32;
- u64 prev = *ptr;
-
- asm volatile("\n1:\t"
- LOCK_PREFIX "cmpxchg8b %0\n\t"
- "jnz 1b"
- : "=m" (*ptr), "+A" (prev)
- : "b" (low), "c" (high)
- : "memory");
-}
-
#ifdef CONFIG_X86_CMPXCHG64
#define arch_cmpxchg64(ptr, o, n) \
((__typeof__(*(ptr)))__cmpxchg64((ptr), (unsigned long long)(o), \
--- a/arch/x86/include/asm/pgtable-3level.h
+++ b/arch/x86/include/asm/pgtable-3level.h
@@ -19,7 +19,15 @@
pr_err("%s:%d: bad pgd %p(%016Lx)\n", \
__FILE__, __LINE__, &(e), pgd_val(e))

-/* Rules for using set_pte: the pte being assigned *must* be
+#define pxx_xchg64(_pxx, _ptr, _val) ({ \
+ _pxx##val_t *_p = (_pxx##val_t *)_ptr; \
+ _pxx##val_t _o = *_p; \
+ do { } while (!try_cmpxchg64(_p, &_o, (_val))); \
+ native_make_##_pxx(_o); \
+})
+
+/*
+ * Rules for using set_pte: the pte being assigned *must* be
* either not present or in a state where the hardware will
* not attempt to update the pte. In places where this is
* not possible, use pte_get_and_clear to obtain the old pte
@@ -34,12 +42,12 @@ static inline void native_set_pte(pte_t

static inline void native_set_pte_atomic(pte_t *ptep, pte_t pte)
{
- set_64bit((unsigned long long *)(ptep), native_pte_val(pte));
+ pxx_xchg64(pte, ptep, native_pte_val(pte));
}

static inline void native_set_pmd(pmd_t *pmdp, pmd_t pmd)
{
- set_64bit((unsigned long long *)(pmdp), native_pmd_val(pmd));
+ pxx_xchg64(pmd, pmdp, native_pmd_val(pmd));
}

static inline void native_set_pud(pud_t *pudp, pud_t pud)
@@ -47,7 +55,7 @@ static inline void native_set_pud(pud_t
#ifdef CONFIG_PAGE_TABLE_ISOLATION
pud.p4d.pgd = pti_set_user_pgtbl(&pudp->p4d.pgd, pud.p4d.pgd);
#endif
- set_64bit((unsigned long long *)(pudp), native_pud_val(pud));
+ pxx_xchg64(pud, pudp, native_pud_val(pud));
}

/*
@@ -91,13 +99,6 @@ static inline void pud_clear(pud_t *pudp
}

-#define pxx_xchg64(_pxx, _ptr, _val) ({ \
- _pxx##val_t *_p = (_pxx##val_t *)_ptr; \
- _pxx##val_t _o = *_p; \
- do { } while (!try_cmpxchg64(_p, &_o, (_val))); \
- native_make_##_pxx(_o); \
-})
-
#ifdef CONFIG_SMP
static inline pte_t native_ptep_get_and_clear(pte_t *ptep)
{