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/lppaca.h>
10 #include <asm/hvcall.h>
11 #endif
12 
13 #ifdef CONFIG_PPC_SPLPAR
14 #include <linux/smp.h>
15 #include <asm/kvm_guest.h>
16 #include <asm/cputhreads.h>
17 
18 DECLARE_STATIC_KEY_FALSE(shared_processor);
19 
20 static inline bool is_shared_processor(void)
21 {
22 	return static_branch_unlikely(&shared_processor);
23 }
24 
25 #ifdef CONFIG_PARAVIRT_TIME_ACCOUNTING
26 extern struct static_key paravirt_steal_enabled;
27 extern struct static_key paravirt_steal_rq_enabled;
28 
29 u64 pseries_paravirt_steal_clock(int cpu);
30 
31 static inline u64 paravirt_steal_clock(int cpu)
32 {
33 	return pseries_paravirt_steal_clock(cpu);
34 }
35 #endif
36 
37 /* If bit 0 is set, the cpu has been ceded, conferred, or preempted */
38 static inline u32 yield_count_of(int cpu)
39 {
40 	__be32 yield_count = READ_ONCE(lppaca_of(cpu).yield_count);
41 	return be32_to_cpu(yield_count);
42 }
43 
44 /*
45  * Spinlock code confers and prods, so don't trace the hcalls because the
46  * tracing code takes spinlocks which can cause recursion deadlocks.
47  *
48  * These calls are made while the lock is not held: the lock slowpath yields if
49  * it can not acquire the lock, and unlock slow path might prod if a waiter has
50  * yielded). So this may not be a problem for simple spin locks because the
51  * tracing does not technically recurse on the lock, but we avoid it anyway.
52  *
53  * However the queued spin lock contended path is more strictly ordered: the
54  * H_CONFER hcall is made after the task has queued itself on the lock, so then
55  * recursing on that lock will cause the task to then queue up again behind the
56  * first instance (or worse: queued spinlocks use tricks that assume a context
57  * never waits on more than one spinlock, so such recursion may cause random
58  * corruption in the lock code).
59  */
60 static inline void yield_to_preempted(int cpu, u32 yield_count)
61 {
62 	plpar_hcall_norets_notrace(H_CONFER, get_hard_smp_processor_id(cpu), yield_count);
63 }
64 
65 static inline void prod_cpu(int cpu)
66 {
67 	plpar_hcall_norets_notrace(H_PROD, get_hard_smp_processor_id(cpu));
68 }
69 
70 static inline void yield_to_any(void)
71 {
72 	plpar_hcall_norets_notrace(H_CONFER, -1, 0);
73 }
74 #else
75 static inline bool is_shared_processor(void)
76 {
77 	return false;
78 }
79 
80 static inline u32 yield_count_of(int cpu)
81 {
82 	return 0;
83 }
84 
85 extern void ___bad_yield_to_preempted(void);
86 static inline void yield_to_preempted(int cpu, u32 yield_count)
87 {
88 	___bad_yield_to_preempted(); /* This would be a bug */
89 }
90 
91 extern void ___bad_yield_to_any(void);
92 static inline void yield_to_any(void)
93 {
94 	___bad_yield_to_any(); /* This would be a bug */
95 }
96 
97 extern void ___bad_prod_cpu(void);
98 static inline void prod_cpu(int cpu)
99 {
100 	___bad_prod_cpu(); /* This would be a bug */
101 }
102 
103 #endif
104 
105 #define vcpu_is_preempted vcpu_is_preempted
106 static inline bool vcpu_is_preempted(int cpu)
107 {
108 	/*
109 	 * The dispatch/yield bit alone is an imperfect indicator of
110 	 * whether the hypervisor has dispatched @cpu to run on a physical
111 	 * processor. When it is clear, @cpu is definitely not preempted.
112 	 * But when it is set, it means only that it *might* be, subject to
113 	 * other conditions. So we check other properties of the VM and
114 	 * @cpu first, resorting to the yield count last.
115 	 */
116 
117 	/*
118 	 * Hypervisor preemption isn't possible in dedicated processor
119 	 * mode by definition.
120 	 */
121 	if (!is_shared_processor())
122 		return false;
123 
124 #ifdef CONFIG_PPC_SPLPAR
125 	if (!is_kvm_guest()) {
126 		int first_cpu;
127 
128 		/*
129 		 * The result of vcpu_is_preempted() is used in a
130 		 * speculative way, and is always subject to invalidation
131 		 * by events internal and external to Linux. While we can
132 		 * be called in preemptable context (in the Linux sense),
133 		 * we're not accessing per-cpu resources in a way that can
134 		 * race destructively with Linux scheduler preemption and
135 		 * migration, and callers can tolerate the potential for
136 		 * error introduced by sampling the CPU index without
137 		 * pinning the task to it. So it is permissible to use
138 		 * raw_smp_processor_id() here to defeat the preempt debug
139 		 * warnings that can arise from using smp_processor_id()
140 		 * in arbitrary contexts.
141 		 */
142 		first_cpu = cpu_first_thread_sibling(raw_smp_processor_id());
143 
144 		/*
145 		 * The PowerVM hypervisor dispatches VMs on a whole core
146 		 * basis. So we know that a thread sibling of the local CPU
147 		 * cannot have been preempted by the hypervisor, even if it
148 		 * has called H_CONFER, which will set the yield bit.
149 		 */
150 		if (cpu_first_thread_sibling(cpu) == first_cpu)
151 			return false;
152 	}
153 #endif
154 
155 	if (yield_count_of(cpu) & 1)
156 		return true;
157 	return false;
158 }
159 
160 static inline bool pv_is_native_spin_unlock(void)
161 {
162 	return !is_shared_processor();
163 }
164 
165 #endif /* _ASM_POWERPC_PARAVIRT_H */
166