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Message-Id: <20220113233940.3608440-3-posk@google.com>
Date: Thu, 13 Jan 2022 15:39:37 -0800
From: Peter Oskolkov <posk@...gle.com>
To: Peter Zijlstra <peterz@...radead.org>, mingo@...hat.com,
tglx@...utronix.de, juri.lelli@...hat.com,
vincent.guittot@...aro.org, dietmar.eggemann@....com,
rostedt@...dmis.org, bsegall@...gle.com, mgorman@...e.de,
bristot@...hat.com
Cc: linux-kernel@...r.kernel.org, linux-mm@...ck.org,
linux-api@...r.kernel.org, x86@...nel.org, pjt@...gle.com,
posk@...gle.com, avagin@...gle.com, jannh@...gle.com,
tdelisle@...terloo.ca, posk@...k.io
Subject: [RFC PATCH v2 2/5] x86/uaccess: Implement unsafe_try_cmpxchg_user()
From: Peter Zijlstra <peterz@...radead.org>
Do try_cmpxchg() loops on userspace addresses.
Signed-off-by: Peter Zijlstra (Intel) <peterz@...radead.org>
---
arch/x86/include/asm/uaccess.h | 57 ++++++++++++++++++++++++++++++++++
1 file changed, 57 insertions(+)
diff --git a/arch/x86/include/asm/uaccess.h b/arch/x86/include/asm/uaccess.h
index ac96f9b2d64b..8277ec05be02 100644
--- a/arch/x86/include/asm/uaccess.h
+++ b/arch/x86/include/asm/uaccess.h
@@ -342,6 +342,24 @@ do { \
: [umem] "m" (__m(addr)) \
: : label)
+#define __try_cmpxchg_user_asm(itype, _ptr, _pold, _new, label) ({ \
+ bool success; \
+ __typeof__(_ptr) _old = (__typeof__(_ptr))(_pold); \
+ __typeof__(*(_ptr)) __old = *_old; \
+ __typeof__(*(_ptr)) __new = (_new); \
+ asm_volatile_goto("\n" \
+ "1: " LOCK_PREFIX "cmpxchg"itype" %[new], %[ptr]\n"\
+ _ASM_EXTABLE_UA(1b, %l[label]) \
+ : CC_OUT(z) (success), \
+ [ptr] "+m" (*_ptr), \
+ [old] "+a" (__old) \
+ : [new] "r" (__new) \
+ : "memory", "cc" \
+ : label); \
+ if (unlikely(!success)) \
+ *_old = __old; \
+ likely(success); })
+
#else // !CONFIG_CC_HAS_ASM_GOTO_OUTPUT
#ifdef CONFIG_X86_32
@@ -407,6 +425,30 @@ do { \
: [umem] "m" (__m(addr)), \
"0" (err))
+#define __try_cmpxchg_user_asm(itype, _ptr, _pold, _new, label) ({ \
+ int __err = 0; \
+ bool success; \
+ __typeof__(_ptr) _old = (__typeof__(_ptr))(_pold); \
+ __typeof__(*(_ptr)) __old = *_old; \
+ __typeof__(*(_ptr)) __new = (_new); \
+ asm volatile("\n" \
+ "1: " LOCK_PREFIX "cmpxchg"itype" %[new], %[ptr]\n"\
+ CC_SET(z) \
+ "2:\n" \
+ _ASM_EXTABLE_TYPE_REG(1b, 2b, EX_TYPE_EFAULT_REG, \
+ %[errout]) \
+ : CC_OUT(z) (success), \
+ [errout] "+r" (__err), \
+ [ptr] "+m" (*_ptr), \
+ [old] "+a" (__old) \
+ : [new] "r" (__new) \
+ : "memory", "cc"); \
+ if (unlikely(__err)) \
+ goto label; \
+ if (unlikely(!success)) \
+ *_old = __old; \
+ likely(success); })
+
#endif // CONFIG_CC_HAS_ASM_GOTO_OUTPUT
/* FIXME: this hack is definitely wrong -AK */
@@ -501,6 +543,21 @@ do { \
} while (0)
#endif // CONFIG_CC_HAS_ASM_GOTO_OUTPUT
+extern void __try_cmpxchg_user_wrong_size(void);
+
+#define unsafe_try_cmpxchg_user(_ptr, _oldp, _nval, _label) ({ \
+ __typeof__(*(_ptr)) __ret; \
+ switch (sizeof(__ret)) { \
+ case 4: __ret = __try_cmpxchg_user_asm("l", (_ptr), (_oldp), \
+ (_nval), _label); \
+ break; \
+ case 8: __ret = __try_cmpxchg_user_asm("q", (_ptr), (_oldp), \
+ (_nval), _label); \
+ break; \
+ default: __try_cmpxchg_user_wrong_size(); \
+ } \
+ __ret; })
+
/*
* We want the unsafe accessors to always be inlined and use
* the error labels - thus the macro games.
--
2.34.1.703.g22d0c6ccf7-goog
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