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