1 /* SPDX-License-Identifier: GPL-2.0 */ 2 #ifndef __ASM_PREEMPT_H 3 #define __ASM_PREEMPT_H 4 5 #include <asm/current.h> 6 #include <linux/thread_info.h> 7 #include <asm/atomic_ops.h> 8 #include <asm/cmpxchg.h> 9 #include <asm/march.h> 10 11 /* 12 * Use MSB so it is possible to read preempt_count with LLGT which 13 * reads the least significant 31 bits with a single instruction. 14 */ 15 #define PREEMPT_NEED_RESCHED 0x80000000 16 17 /* 18 * We use the PREEMPT_NEED_RESCHED bit as an inverted NEED_RESCHED such 19 * that a decrement hitting 0 means we can and should reschedule. 20 */ 21 #define PREEMPT_ENABLED (0 + PREEMPT_NEED_RESCHED) 22 23 /* 24 * We mask the PREEMPT_NEED_RESCHED bit so as not to confuse all current users 25 * that think a non-zero value indicates we cannot preempt. 26 */ 27 static __always_inline int preempt_count(void) 28 { 29 unsigned long lc_preempt, count; 30 31 BUILD_BUG_ON(sizeof_field(struct lowcore, preempt_count) != sizeof(int)); 32 lc_preempt = offsetof(struct lowcore, preempt_count); 33 /* READ_ONCE(get_lowcore()->preempt_count) & ~PREEMPT_NEED_RESCHED */ 34 asm_inline( 35 ALTERNATIVE("llgt %[count],%[offzero](%%r0)\n", 36 "llgt %[count],%[offalt](%%r0)\n", 37 ALT_FEATURE(MFEATURE_LOWCORE)) 38 : [count] "=d" (count) 39 : [offzero] "i" (lc_preempt), 40 [offalt] "i" (lc_preempt + LOWCORE_ALT_ADDRESS), 41 "m" (((struct lowcore *)0)->preempt_count)); 42 return count; 43 } 44 45 static __always_inline void preempt_count_set(int pc) 46 { 47 int old, new; 48 49 old = READ_ONCE(get_lowcore()->preempt_count); 50 do { 51 new = (old & PREEMPT_NEED_RESCHED) | (pc & ~PREEMPT_NEED_RESCHED); 52 } while (!arch_try_cmpxchg(&get_lowcore()->preempt_count, &old, new)); 53 } 54 55 /* 56 * We fold the NEED_RESCHED bit into the preempt count such that 57 * preempt_enable() can decrement and test for needing to reschedule with a 58 * short instruction sequence. 59 * 60 * We invert the actual bit, so that when the decrement hits 0 we know we both 61 * need to resched (the bit is cleared) and can resched (no preempt count). 62 */ 63 64 static __always_inline void set_preempt_need_resched(void) 65 { 66 __atomic_and(~PREEMPT_NEED_RESCHED, &get_lowcore()->preempt_count); 67 } 68 69 static __always_inline void clear_preempt_need_resched(void) 70 { 71 __atomic_or(PREEMPT_NEED_RESCHED, &get_lowcore()->preempt_count); 72 } 73 74 static __always_inline bool test_preempt_need_resched(void) 75 { 76 return !(READ_ONCE(get_lowcore()->preempt_count) & PREEMPT_NEED_RESCHED); 77 } 78 79 static __always_inline void __preempt_count_add(int val) 80 { 81 /* 82 * With some obscure config options and CONFIG_PROFILE_ALL_BRANCHES 83 * enabled, gcc 12 fails to handle __builtin_constant_p(). 84 */ 85 if (!IS_ENABLED(CONFIG_PROFILE_ALL_BRANCHES)) { 86 if (__builtin_constant_p(val) && (val >= -128) && (val <= 127)) { 87 unsigned long lc_preempt; 88 89 lc_preempt = offsetof(struct lowcore, preempt_count); 90 asm_inline( 91 ALTERNATIVE("asi %[offzero](%%r0),%[val]\n", 92 "asi %[offalt](%%r0),%[val]\n", 93 ALT_FEATURE(MFEATURE_LOWCORE)) 94 : "+m" (((struct lowcore *)0)->preempt_count) 95 : [offzero] "i" (lc_preempt), [val] "i" (val), 96 [offalt] "i" (lc_preempt + LOWCORE_ALT_ADDRESS) 97 : "cc"); 98 return; 99 } 100 } 101 __atomic_add(val, &get_lowcore()->preempt_count); 102 } 103 104 static __always_inline void __preempt_count_sub(int val) 105 { 106 __preempt_count_add(-val); 107 } 108 109 /* 110 * Because we keep PREEMPT_NEED_RESCHED set when we do _not_ need to reschedule 111 * a decrement which hits zero means we have no preempt_count and should 112 * reschedule. 113 */ 114 static __always_inline bool __preempt_count_dec_and_test(void) 115 { 116 #ifdef __HAVE_ASM_FLAG_OUTPUTS__ 117 unsigned long lc_preempt; 118 int cc; 119 120 lc_preempt = offsetof(struct lowcore, preempt_count); 121 asm_inline( 122 ALTERNATIVE("alsi %[offzero](%%r0),%[val]\n", 123 "alsi %[offalt](%%r0),%[val]\n", 124 ALT_FEATURE(MFEATURE_LOWCORE)) 125 : "=@cc" (cc), "+m" (((struct lowcore *)0)->preempt_count) 126 : [offzero] "i" (lc_preempt), [val] "i" (-1), 127 [offalt] "i" (lc_preempt + LOWCORE_ALT_ADDRESS)); 128 return (cc == 0) || (cc == 2); 129 #else 130 return __atomic_add_const_and_test(-1, &get_lowcore()->preempt_count); 131 #endif 132 } 133 134 /* 135 * Returns true when we need to resched and can (barring IRQ state). 136 */ 137 static __always_inline bool should_resched(int preempt_offset) 138 { 139 return unlikely(READ_ONCE(get_lowcore()->preempt_count) == preempt_offset); 140 } 141 142 #define init_task_preempt_count(p) do { } while (0) 143 /* Deferred to CPU bringup time */ 144 #define init_idle_preempt_count(p, cpu) do { } while (0) 145 146 #ifdef CONFIG_PREEMPTION 147 148 void preempt_schedule(void); 149 void preempt_schedule_notrace(void); 150 151 #ifdef CONFIG_PREEMPT_DYNAMIC 152 153 void dynamic_preempt_schedule(void); 154 void dynamic_preempt_schedule_notrace(void); 155 #define __preempt_schedule() dynamic_preempt_schedule() 156 #define __preempt_schedule_notrace() dynamic_preempt_schedule_notrace() 157 158 #else /* CONFIG_PREEMPT_DYNAMIC */ 159 160 #define __preempt_schedule() preempt_schedule() 161 #define __preempt_schedule_notrace() preempt_schedule_notrace() 162 163 #endif /* CONFIG_PREEMPT_DYNAMIC */ 164 165 #endif /* CONFIG_PREEMPTION */ 166 167 #endif /* __ASM_PREEMPT_H */ 168