linux-kernel - [RFC][PATCH 7/9] x86/mm/pae: Dont (ab)use atomic64

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Message-ID: <20201130113603.205586001@infradead.org>
Date:   Mon, 30 Nov 2020 12:27:12 +0100
From:   Peter Zijlstra <peterz@...radead.org>
To:     x86@...nel.org, willy@...radead.org
Cc:     linux-mm@...ck.org, linux-kernel@...r.kernel.org,
        aarcange@...hat.com, kirill.shutemov@...ux.intel.com,
        jroedel@...e.de, peterz@...radead.org
Subject: [RFC][PATCH 7/9] x86/mm/pae: Dont (ab)use atomic64

PAE implies CX8, write readable code.

Signed-off-by: Peter Zijlstra (Intel) <peterz@...radead.org>
---
 arch/x86/include/asm/pgtable-3level.h |   10 +++++-----
 1 file changed, 5 insertions(+), 5 deletions(-)

--- a/arch/x86/include/asm/pgtable-3level.h
+++ b/arch/x86/include/asm/pgtable-3level.h
@@ -2,8 +2,6 @@
 #ifndef _ASM_X86_PGTABLE_3LEVEL_H
 #define _ASM_X86_PGTABLE_3LEVEL_H
 
-#include <asm/atomic64_32.h>
-
 /*
  * Intel Physical Address Extension (PAE) Mode - three-level page
  * tables on PPro+ CPUs.
@@ -96,11 +94,13 @@ static inline void pud_clear(pud_t *pudp
 #ifdef CONFIG_SMP
 static inline pte_t native_ptep_get_and_clear(pte_t *ptep)
 {
-	pte_t res;
+	pte_t old;
 
-	res.pte = (pteval_t)arch_atomic64_xchg((atomic64_t *)ptep, 0);
+	do {
+		old = *ptep;
+	} while (cmpxchg64(&ptep->pte, old.pte, 0ULL) != old.pte);
 
-	return res;
+	return old;
 }
 #else
 #define native_ptep_get_and_clear(xp) native_local_ptep_get_and_clear(xp)