Re: [PATCH 2/3] locking/atomic/x86: Introduce arch_try_cmpxchg64()

Uros Bizjak
2020-12-15T20:10:22Z

On Tue, Dec 15, 2020 at 7:28 PM Uros Bizjak <ubizjak@gmail.com> wrote:
>
> Add arch_try_cmpxchg64(), similar to arch_try_cmpxchg(), that
> operates with 64 bit operands. This function provides the same
> interface for 32 bit and 64 bit targets.
>
> Signed-off-by: Uros Bizjak <ubizjak@gmail.com>
> Cc: Thomas Gleixner <tglx@linutronix.de>
> Cc: Ingo Molnar <mingo@redhat.com>
> Cc: Borislav Petkov <bp@alien8.de>
> Cc: "H. Peter Anvin" <hpa@zytor.com>
> ---
> arch/x86/include/asm/cmpxchg_32.h | 62 ++++++++++++++++++++++++++-----
> arch/x86/include/asm/cmpxchg_64.h | 6 +++
> 2 files changed, 59 insertions(+), 9 deletions(-)
>
> diff --git a/arch/x86/include/asm/cmpxchg_32.h b/arch/x86/include/asm/cmpxchg_32.h
> index 0a7fe0321613..8dcde400244e 100644
> --- a/arch/x86/include/asm/cmpxchg_32.h
> +++ b/arch/x86/include/asm/cmpxchg_32.h
> @@ -35,15 +35,6 @@ static inline void set_64bit(volatile u64 *ptr, u64 value)
> : "memory");
> }
>
> -#ifdef CONFIG_X86_CMPXCHG64

Oops, I didn't notice that I had left a reversed #ifdef condition in
the patch (to test 32 bit target without X86_CMPXCHG64).

Obviously, CONFIG_X86_CMPXCHG64 has to be defined to use CMPXCHG8B, so
please use #ifdef here.

Uros.

> -#define arch_cmpxchg64(ptr, o, n) \
> - ((__typeof__(*(ptr)))__cmpxchg64((ptr), (unsigned long long)(o), \
> - (unsigned long long)(n)))
> -#define arch_cmpxchg64_local(ptr, o, n) \
> - ((__typeof__(*(ptr)))__cmpxchg64_local((ptr), (unsigned long long)(o), \
> - (unsigned long long)(n)))
> -#endif
> -
> static inline u64 __cmpxchg64(volatile u64 *ptr, u64 old, u64 new)
> {
> u64 prev;
> @@ -71,6 +62,39 @@ static inline u64 __cmpxchg64_local(volatile u64 *ptr, u64 old, u64 new)
> }
>
> #ifndef CONFIG_X86_CMPXCHG64
> +#define arch_cmpxchg64(ptr, o, n) \
> + ((__typeof__(*(ptr)))__cmpxchg64((ptr), (unsigned long long)(o), \
> + (unsigned long long)(n)))
> +#define arch_cmpxchg64_local(ptr, o, n) \
> + ((__typeof__(*(ptr)))__cmpxchg64_local((ptr), (unsigned long long)(o), \
> +
> +#define __raw_try_cmpxchg64(_ptr, _pold, _new, lock) \
> +({ \
> + bool success; \
> + __typeof__(_ptr) _old = (__typeof__(_ptr))(_pold); \
> + __typeof__(*(_ptr)) __old = *_old; \
> + __typeof__(*(_ptr)) __new = (_new); \
> + asm volatile(lock "cmpxchg8b %1" \
> + CC_SET(z) \
> + : CC_OUT(z) (success), \
> + "+m" (*_ptr), \
> + "+A" (__old) \
> + : "b" ((unsigned int)__new), \
> + "c" ((unsigned int)(__new>>32)) \
> + : "memory"); \
> + if (unlikely(!success)) \
> + *_old = __old; \
> + likely(success); \
> +})
> +
> +#define __try_cmpxchg64(ptr, pold, new) \
> + __raw_try_cmpxchg64((ptr), (pold), (new), LOCK_PREFIX)
> +
> +#define arch_try_cmpxchg64(ptr, pold, new) \
> + __try_cmpxchg64((ptr), (pold), (new))
> +
> +#else
> +
> /*
> * Building a kernel capable running on 80386 and 80486. It may be necessary
> * to simulate the cmpxchg8b on the 80386 and 80486 CPU.
> @@ -108,6 +132,26 @@ static inline u64 __cmpxchg64_local(volatile u64 *ptr, u64 old, u64 new)
> : "memory"); \
> __ret; })
>
> +#define arch_try_cmpxchg64(ptr, po, n) \
> +({ \
> + bool success; \
> + __typeof__(ptr) _old = (__typeof__(ptr))(po); \
> + __typeof__(*(ptr)) __old = *_old; \
> + __typeof__(*(ptr)) __new = (n); \
> + alternative_io(LOCK_PREFIX_HERE \
> + "call cmpxchg8b_emu", \
> + "lock; cmpxchg8b (%%esi)" , \
> + X86_FEATURE_CX8, \
> + "+A" (__old), \
> + "S" ((ptr)), \
> + "b" ((unsigned int)__new), \
> + "c" ((unsigned int)(__new>>32)) \
> + : "memory"); \
> + success = (__old == *_old); \
> + if (unlikely(!success)) \
> + *_old = __old; \
> + likely(success); \
> +})
> #endif
>
> #define system_has_cmpxchg_double() boot_cpu_has(X86_FEATURE_CX8)
> diff --git a/arch/x86/include/asm/cmpxchg_64.h b/arch/x86/include/asm/cmpxchg_64.h
> index 072e5459fe2f..250187ac8248 100644
> --- a/arch/x86/include/asm/cmpxchg_64.h
> +++ b/arch/x86/include/asm/cmpxchg_64.h
> @@ -19,6 +19,12 @@ static inline void set_64bit(volatile u64 *ptr, u64 val)
> arch_cmpxchg_local((ptr), (o), (n)); \
> })
>
> +#define arch_try_cmpxchg64(ptr, po, n) \
> +({ \
> + BUILD_BUG_ON(sizeof(*(ptr)) != 8); \
> + arch_try_cmpxchg((ptr), (po), (n)); \
> +})
> +
> #define system_has_cmpxchg_double() boot_cpu_has(X86_FEATURE_CX16)
>
> #endif /* _ASM_X86_CMPXCHG_64_H */
> --
> 2.26.2
>