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
18DECLARE_STATIC_KEY_FALSE(shared_processor);
19
20static inline bool is_shared_processor(void)
21{
22	return static_branch_unlikely(&shared_processor);
23}
24
25#ifdef CONFIG_PARAVIRT_TIME_ACCOUNTING
26extern struct static_key paravirt_steal_enabled;
27extern struct static_key paravirt_steal_rq_enabled;
28
29u64 pseries_paravirt_steal_clock(int cpu);
30
31static 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 */
38static 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 */
60static 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
65static inline void prod_cpu(int cpu)
66{
67	plpar_hcall_norets_notrace(H_PROD, get_hard_smp_processor_id(cpu));
68}
69
70static inline void yield_to_any(void)
71{
72	plpar_hcall_norets_notrace(H_CONFER, -1, 0);
73}
74#else
75static inline bool is_shared_processor(void)
76{
77	return false;
78}
79
80static inline u32 yield_count_of(int cpu)
81{
82	return 0;
83}
84
85extern void ___bad_yield_to_preempted(void);
86static inline void yield_to_preempted(int cpu, u32 yield_count)
87{
88	___bad_yield_to_preempted(); /* This would be a bug */
89}
90
91extern void ___bad_yield_to_any(void);
92static inline void yield_to_any(void)
93{
94	___bad_yield_to_any(); /* This would be a bug */
95}
96
97extern void ___bad_prod_cpu(void);
98static 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
106static 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
160static inline bool pv_is_native_spin_unlock(void)
161{
162	return !is_shared_processor();
163}
164
165#endif /* _ASM_POWERPC_PARAVIRT_H */
166