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
75 static inline bool is_vcpu_idle(int vcpu)
76 {
77 return lppaca_of(vcpu).idle;
78 }
79
80 static inline bool vcpu_is_dispatched(int vcpu)
81 {
82 /*
83 * This is the yield_count. An "odd" value (low bit on) means that
84 * the processor is yielded (either because of an OS yield or a
85 * hypervisor preempt). An even value implies that the processor is
86 * currently executing.
87 */
88 return (!(yield_count_of(vcpu) & 1));
89 }
90 #else
91 static inline bool is_shared_processor(void)
92 {
93 return false;
94 }
95
96 static inline u32 yield_count_of(int cpu)
97 {
98 return 0;
99 }
100
101 extern void ___bad_yield_to_preempted(void);
102 static inline void yield_to_preempted(int cpu, u32 yield_count)
103 {
104 ___bad_yield_to_preempted(); /* This would be a bug */
105 }
106
107 extern void ___bad_yield_to_any(void);
108 static inline void yield_to_any(void)
109 {
110 ___bad_yield_to_any(); /* This would be a bug */
111 }
112
113 extern void ___bad_prod_cpu(void);
114 static inline void prod_cpu(int cpu)
115 {
116 ___bad_prod_cpu(); /* This would be a bug */
117 }
118
119 static inline bool is_vcpu_idle(int vcpu)
120 {
121 return false;
122 }
123 static inline bool vcpu_is_dispatched(int vcpu)
124 {
125 return true;
126 }
127 #endif
128
129 #define vcpu_is_preempted vcpu_is_preempted
130 static inline bool vcpu_is_preempted(int cpu)
131 {
132 /*
133 * The dispatch/yield bit alone is an imperfect indicator of
134 * whether the hypervisor has dispatched @cpu to run on a physical
135 * processor. When it is clear, @cpu is definitely not preempted.
136 * But when it is set, it means only that it *might* be, subject to
137 * other conditions. So we check other properties of the VM and
138 * @cpu first, resorting to the yield count last.
139 */
140
141 /*
142 * Hypervisor preemption isn't possible in dedicated processor
143 * mode by definition.
144 */
145 if (!is_shared_processor())
146 return false;
147
148 /*
149 * If the hypervisor has dispatched the target CPU on a physical
150 * processor, then the target CPU is definitely not preempted.
151 */
152 if (vcpu_is_dispatched(cpu))
153 return false;
154
155 /*
156 * if the target CPU is not dispatched and the guest OS
157 * has not marked the CPU idle, then it is hypervisor preempted.
158 */
159 if (!is_vcpu_idle(cpu))
160 return true;
161
162 #ifdef CONFIG_PPC_SPLPAR
163 if (!is_kvm_guest()) {
164 int first_cpu, i;
165
166 /*
167 * The result of vcpu_is_preempted() is used in a
168 * speculative way, and is always subject to invalidation
169 * by events internal and external to Linux. While we can
170 * be called in preemptable context (in the Linux sense),
171 * we're not accessing per-cpu resources in a way that can
172 * race destructively with Linux scheduler preemption and
173 * migration, and callers can tolerate the potential for
174 * error introduced by sampling the CPU index without
175 * pinning the task to it. So it is permissible to use
176 * raw_smp_processor_id() here to defeat the preempt debug
177 * warnings that can arise from using smp_processor_id()
178 * in arbitrary contexts.
179 */
180 first_cpu = cpu_first_thread_sibling(raw_smp_processor_id());
181
182 /*
183 * The PowerVM hypervisor dispatches VMs on a whole core
184 * basis. So we know that a thread sibling of the executing CPU
185 * cannot have been preempted by the hypervisor, even if it
186 * has called H_CONFER, which will set the yield bit.
187 */
188 if (cpu_first_thread_sibling(cpu) == first_cpu)
189 return false;
190
191 /*
192 * The specific target CPU was marked by guest OS as idle, but
193 * then also check all other cpus in the core for PowerVM
194 * because it does core scheduling and one of the vcpu
195 * of the core getting preempted by hypervisor implies
196 * other vcpus can also be considered preempted.
197 */
198 first_cpu = cpu_first_thread_sibling(cpu);
199 for (i = first_cpu; i < first_cpu + threads_per_core; i++) {
200 if (i == cpu)
201 continue;
202 if (vcpu_is_dispatched(i))
203 return false;
204 if (!is_vcpu_idle(i))
205 return true;
206 }
207 }
208 #endif
209
210 /*
211 * None of the threads in target CPU's core are running but none of
212 * them were preempted too. Hence assume the target CPU to be
213 * non-preempted.
214 */
215 return false;
216 }
217
218 static inline bool pv_is_native_spin_unlock(void)
219 {
220 return !is_shared_processor();
221 }
222
223 #endif /* _ASM_POWERPC_PARAVIRT_H */
224
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