diff options
Diffstat (limited to 'arch/arm64/include')
-rw-r--r-- | arch/arm64/include/asm/rwonce.h | 73 |
1 files changed, 73 insertions, 0 deletions
diff --git a/arch/arm64/include/asm/rwonce.h b/arch/arm64/include/asm/rwonce.h new file mode 100644 index 000000000000..1bce62fa908a --- /dev/null +++ b/arch/arm64/include/asm/rwonce.h @@ -0,0 +1,73 @@ +/* SPDX-License-Identifier: GPL-2.0 */ +/* + * Copyright (C) 2020 Google LLC. + */ +#ifndef __ASM_RWONCE_H +#define __ASM_RWONCE_H + +#ifdef CONFIG_LTO + +#include <linux/compiler_types.h> +#include <asm/alternative-macros.h> + +#ifndef BUILD_VDSO + +#ifdef CONFIG_AS_HAS_LDAPR +#define __LOAD_RCPC(sfx, regs...) \ + ALTERNATIVE( \ + "ldar" #sfx "\t" #regs, \ + ".arch_extension rcpc\n" \ + "ldapr" #sfx "\t" #regs, \ + ARM64_HAS_LDAPR) +#else +#define __LOAD_RCPC(sfx, regs...) "ldar" #sfx "\t" #regs +#endif /* CONFIG_AS_HAS_LDAPR */ + +/* + * When building with LTO, there is an increased risk of the compiler + * converting an address dependency headed by a READ_ONCE() invocation + * into a control dependency and consequently allowing for harmful + * reordering by the CPU. + * + * Ensure that such transformations are harmless by overriding the generic + * READ_ONCE() definition with one that provides RCpc acquire semantics + * when building with LTO. + */ +#define __READ_ONCE(x) \ +({ \ + typeof(&(x)) __x = &(x); \ + int atomic = 1; \ + union { __unqual_scalar_typeof(*__x) __val; char __c[1]; } __u; \ + switch (sizeof(x)) { \ + case 1: \ + asm volatile(__LOAD_RCPC(b, %w0, %1) \ + : "=r" (*(__u8 *)__u.__c) \ + : "Q" (*__x) : "memory"); \ + break; \ + case 2: \ + asm volatile(__LOAD_RCPC(h, %w0, %1) \ + : "=r" (*(__u16 *)__u.__c) \ + : "Q" (*__x) : "memory"); \ + break; \ + case 4: \ + asm volatile(__LOAD_RCPC(, %w0, %1) \ + : "=r" (*(__u32 *)__u.__c) \ + : "Q" (*__x) : "memory"); \ + break; \ + case 8: \ + asm volatile(__LOAD_RCPC(, %0, %1) \ + : "=r" (*(__u64 *)__u.__c) \ + : "Q" (*__x) : "memory"); \ + break; \ + default: \ + atomic = 0; \ + } \ + atomic ? (typeof(*__x))__u.__val : (*(volatile typeof(__x))__x);\ +}) + +#endif /* !BUILD_VDSO */ +#endif /* CONFIG_LTO */ + +#include <asm-generic/rwonce.h> + +#endif /* __ASM_RWONCE_H */ |