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| -rw-r--r-- | arch/mips/include/asm/sync.h | 209 |
1 files changed, 209 insertions, 0 deletions
diff --git a/arch/mips/include/asm/sync.h b/arch/mips/include/asm/sync.h new file mode 100644 index 000000000..aabd09793 --- /dev/null +++ b/arch/mips/include/asm/sync.h @@ -0,0 +1,209 @@ +/* SPDX-License-Identifier: GPL-2.0-only */ +#ifndef __MIPS_ASM_SYNC_H__ +#define __MIPS_ASM_SYNC_H__ + +/* + * sync types are defined by the MIPS64 Instruction Set documentation in Volume + * II-A of the MIPS Architecture Reference Manual, which can be found here: + * + * https://www.mips.com/?do-download=the-mips64-instruction-set-v6-06 + * + * Two types of barrier are provided: + * + * 1) Completion barriers, which ensure that a memory operation has actually + * completed & often involve stalling the CPU pipeline to do so. + * + * 2) Ordering barriers, which only ensure that affected memory operations + * won't be reordered in the CPU pipeline in a manner that violates the + * restrictions imposed by the barrier. + * + * Ordering barriers can be more efficient than completion barriers, since: + * + * a) Ordering barriers only require memory access instructions which preceed + * them in program order (older instructions) to reach a point in the + * load/store datapath beyond which reordering is not possible before + * allowing memory access instructions which follow them (younger + * instructions) to be performed. That is, older instructions don't + * actually need to complete - they just need to get far enough that all + * other coherent CPUs will observe their completion before they observe + * the effects of younger instructions. + * + * b) Multiple variants of ordering barrier are provided which allow the + * effects to be restricted to different combinations of older or younger + * loads or stores. By way of example, if we only care that stores older + * than a barrier are observed prior to stores that are younger than a + * barrier & don't care about the ordering of loads then the 'wmb' + * ordering barrier can be used. Limiting the barrier's effects to stores + * allows loads to continue unaffected & potentially allows the CPU to + * make progress faster than if younger loads had to wait for older stores + * to complete. + */ + +/* + * No sync instruction at all; used to allow code to nullify the effect of the + * __SYNC() macro without needing lots of #ifdefery. + */ +#define __SYNC_none -1 + +/* + * A full completion barrier; all memory accesses appearing prior to this sync + * instruction in program order must complete before any memory accesses + * appearing after this sync instruction in program order. + */ +#define __SYNC_full 0x00 + +/* + * For now we use a full completion barrier to implement all sync types, until + * we're satisfied that lightweight ordering barriers defined by MIPSr6 are + * sufficient to uphold our desired memory model. + */ +#define __SYNC_aq __SYNC_full +#define __SYNC_rl __SYNC_full +#define __SYNC_mb __SYNC_full + +/* + * ...except on Cavium Octeon CPUs, which have been using the 'wmb' ordering + * barrier since 2010 & omit 'rmb' barriers because the CPUs don't perform + * speculative reads. + */ +#ifdef CONFIG_CPU_CAVIUM_OCTEON +# define __SYNC_rmb __SYNC_none +# define __SYNC_wmb 0x04 +#else +# define __SYNC_rmb __SYNC_full +# define __SYNC_wmb __SYNC_full +#endif + +/* + * A GINV sync is a little different; it doesn't relate directly to loads or + * stores, but instead causes synchronization of an icache or TLB global + * invalidation operation triggered by the ginvi or ginvt instructions + * respectively. In cases where we need to know that a ginvi or ginvt operation + * has been performed by all coherent CPUs, we must issue a sync instruction of + * this type. Once this instruction graduates all coherent CPUs will have + * observed the invalidation. + */ +#define __SYNC_ginv 0x14 + +/* Trivial; indicate that we always need this sync instruction. */ +#define __SYNC_always (1 << 0) + +/* + * Indicate that we need this sync instruction only on systems with weakly + * ordered memory access. In general this is most MIPS systems, but there are + * exceptions which provide strongly ordered memory. + */ +#ifdef CONFIG_WEAK_ORDERING +# define __SYNC_weak_ordering (1 << 1) +#else +# define __SYNC_weak_ordering 0 +#endif + +/* + * Indicate that we need this sync instruction only on systems where LL/SC + * don't implicitly provide a memory barrier. In general this is most MIPS + * systems. + */ +#ifdef CONFIG_WEAK_REORDERING_BEYOND_LLSC +# define __SYNC_weak_llsc (1 << 2) +#else +# define __SYNC_weak_llsc 0 +#endif + +/* + * Some Loongson 3 CPUs have a bug wherein execution of a memory access (load, + * store or prefetch) in between an LL & SC can cause the SC instruction to + * erroneously succeed, breaking atomicity. Whilst it's unusual to write code + * containing such sequences, this bug bites harder than we might otherwise + * expect due to reordering & speculation: + * + * 1) A memory access appearing prior to the LL in program order may actually + * be executed after the LL - this is the reordering case. + * + * In order to avoid this we need to place a memory barrier (ie. a SYNC + * instruction) prior to every LL instruction, in between it and any earlier + * memory access instructions. + * + * This reordering case is fixed by 3A R2 CPUs, ie. 3A2000 models and later. + * + * 2) If a conditional branch exists between an LL & SC with a target outside + * of the LL-SC loop, for example an exit upon value mismatch in cmpxchg() + * or similar, then misprediction of the branch may allow speculative + * execution of memory accesses from outside of the LL-SC loop. + * + * In order to avoid this we need a memory barrier (ie. a SYNC instruction) + * at each affected branch target. + * + * This case affects all current Loongson 3 CPUs. + * + * The above described cases cause an error in the cache coherence protocol; + * such that the Invalidate of a competing LL-SC goes 'missing' and SC + * erroneously observes its core still has Exclusive state and lets the SC + * proceed. + * + * Therefore the error only occurs on SMP systems. + */ +#ifdef CONFIG_CPU_LOONGSON3_WORKAROUNDS +# define __SYNC_loongson3_war (1 << 31) +#else +# define __SYNC_loongson3_war 0 +#endif + +/* + * Some Cavium Octeon CPUs suffer from a bug that causes a single wmb ordering + * barrier to be ineffective, requiring the use of 2 in sequence to provide an + * effective barrier as noted by commit 6b07d38aaa52 ("MIPS: Octeon: Use + * optimized memory barrier primitives."). Here we specify that the affected + * sync instructions should be emitted twice. + * Note that this expression is evaluated by the assembler (not the compiler), + * and that the assembler evaluates '==' as 0 or -1, not 0 or 1. + */ +#ifdef CONFIG_CPU_CAVIUM_OCTEON +# define __SYNC_rpt(type) (1 - (type == __SYNC_wmb)) +#else +# define __SYNC_rpt(type) 1 +#endif + +/* + * The main event. Here we actually emit a sync instruction of a given type, if + * reason is non-zero. + * + * In future we have the option of emitting entries in a fixups-style table + * here that would allow us to opportunistically remove some sync instructions + * when we detect at runtime that we're running on a CPU that doesn't need + * them. + */ +#ifdef CONFIG_CPU_HAS_SYNC +# define ____SYNC(_type, _reason, _else) \ + .if (( _type ) != -1) && ( _reason ); \ + .set push; \ + .set MIPS_ISA_LEVEL_RAW; \ + .rept __SYNC_rpt(_type); \ + sync _type; \ + .endr; \ + .set pop; \ + .else; \ + _else; \ + .endif +#else +# define ____SYNC(_type, _reason, _else) +#endif + +/* + * Preprocessor magic to expand macros used as arguments before we insert them + * into assembly code. + */ +#ifdef __ASSEMBLY__ +# define ___SYNC(type, reason, else) \ + ____SYNC(type, reason, else) +#else +# define ___SYNC(type, reason, else) \ + __stringify(____SYNC(type, reason, else)) +#endif + +#define __SYNC(type, reason) \ + ___SYNC(__SYNC_##type, __SYNC_##reason, ) +#define __SYNC_ELSE(type, reason, else) \ + ___SYNC(__SYNC_##type, __SYNC_##reason, else) + +#endif /* __MIPS_ASM_SYNC_H__ */ |