1 /* SPDX-License-Identifier: GPL-2.0-or-later */ 2 #ifndef _ASM_POWERPC_PARAVIRT_H 3 #define _ASM_POWERPC_PARAVIRT_H 4 5 #include <linux/jump_label.h> 6 #include <asm/smp.h> 7 #ifdef CONFIG_PPC64 8 #include <asm/paca.h> 9 #include <asm/hvcall.h> 10 #endif 11 12 #ifdef CONFIG_PPC_SPLPAR 13 #include <linux/smp.h> 14 #include <asm/kvm_guest.h> 15 #include <asm/cputhreads.h> 16 17 DECLARE_STATIC_KEY_FALSE(shared_processor); 18 19 static inline bool is_shared_processor(void) 20 { 21 return static_branch_unlikely(&shared_processor); 22 } 23 24 /* If bit 0 is set, the cpu has been ceded, conferred, or preempted */ 25 static inline u32 yield_count_of(int cpu) 26 { 27 __be32 yield_count = READ_ONCE(lppaca_of(cpu).yield_count); 28 return be32_to_cpu(yield_count); 29 } 30 31 /* 32 * Spinlock code confers and prods, so don't trace the hcalls because the 33 * tracing code takes spinlocks which can cause recursion deadlocks. 34 * 35 * These calls are made while the lock is not held: the lock slowpath yields if 36 * it can not acquire the lock, and unlock slow path might prod if a waiter has 37 * yielded). So this may not be a problem for simple spin locks because the 38 * tracing does not technically recurse on the lock, but we avoid it anyway. 39 * 40 * However the queued spin lock contended path is more strictly ordered: the 41 * H_CONFER hcall is made after the task has queued itself on the lock, so then 42 * recursing on that lock will cause the task to then queue up again behind the 43 * first instance (or worse: queued spinlocks use tricks that assume a context 44 * never waits on more than one spinlock, so such recursion may cause random 45 * corruption in the lock code). 46 */ 47 static inline void yield_to_preempted(int cpu, u32 yield_count) 48 { 49 plpar_hcall_norets_notrace(H_CONFER, get_hard_smp_processor_id(cpu), yield_count); 50 } 51 52 static inline void prod_cpu(int cpu) 53 { 54 plpar_hcall_norets_notrace(H_PROD, get_hard_smp_processor_id(cpu)); 55 } 56 57 static inline void yield_to_any(void) 58 { 59 plpar_hcall_norets_notrace(H_CONFER, -1, 0); 60 } 61 #else 62 static inline bool is_shared_processor(void) 63 { 64 return false; 65 } 66 67 static inline u32 yield_count_of(int cpu) 68 { 69 return 0; 70 } 71 72 extern void ___bad_yield_to_preempted(void); 73 static inline void yield_to_preempted(int cpu, u32 yield_count) 74 { 75 ___bad_yield_to_preempted(); /* This would be a bug */ 76 } 77 78 extern void ___bad_yield_to_any(void); 79 static inline void yield_to_any(void) 80 { 81 ___bad_yield_to_any(); /* This would be a bug */ 82 } 83 84 extern void ___bad_prod_cpu(void); 85 static inline void prod_cpu(int cpu) 86 { 87 ___bad_prod_cpu(); /* This would be a bug */ 88 } 89 90 #endif 91 92 #define vcpu_is_preempted vcpu_is_preempted 93 static inline bool vcpu_is_preempted(int cpu) 94 { 95 /* 96 * The dispatch/yield bit alone is an imperfect indicator of 97 * whether the hypervisor has dispatched @cpu to run on a physical 98 * processor. When it is clear, @cpu is definitely not preempted. 99 * But when it is set, it means only that it *might* be, subject to 100 * other conditions. So we check other properties of the VM and 101 * @cpu first, resorting to the yield count last. 102 */ 103 104 /* 105 * Hypervisor preemption isn't possible in dedicated processor 106 * mode by definition. 107 */ 108 if (!is_shared_processor()) 109 return false; 110 111 #ifdef CONFIG_PPC_SPLPAR 112 if (!is_kvm_guest()) { 113 int first_cpu; 114 115 /* 116 * The result of vcpu_is_preempted() is used in a 117 * speculative way, and is always subject to invalidation 118 * by events internal and external to Linux. While we can 119 * be called in preemptable context (in the Linux sense), 120 * we're not accessing per-cpu resources in a way that can 121 * race destructively with Linux scheduler preemption and 122 * migration, and callers can tolerate the potential for 123 * error introduced by sampling the CPU index without 124 * pinning the task to it. So it is permissible to use 125 * raw_smp_processor_id() here to defeat the preempt debug 126 * warnings that can arise from using smp_processor_id() 127 * in arbitrary contexts. 128 */ 129 first_cpu = cpu_first_thread_sibling(raw_smp_processor_id()); 130 131 /* 132 * The PowerVM hypervisor dispatches VMs on a whole core 133 * basis. So we know that a thread sibling of the local CPU 134 * cannot have been preempted by the hypervisor, even if it 135 * has called H_CONFER, which will set the yield bit. 136 */ 137 if (cpu_first_thread_sibling(cpu) == first_cpu) 138 return false; 139 } 140 #endif 141 142 if (yield_count_of(cpu) & 1) 143 return true; 144 return false; 145 } 146 147 static inline bool pv_is_native_spin_unlock(void) 148 { 149 return !is_shared_processor(); 150 } 151 152 #endif /* _ASM_POWERPC_PARAVIRT_H */ 153