paravirt.h

  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
 75static inline bool is_vcpu_idle(int vcpu)
 76{
 77	return lppaca_of(vcpu).idle;
 78}
 79
 80static 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
 91static inline bool is_shared_processor(void)
 92{
 93	return false;
 94}
 95
 96static inline u32 yield_count_of(int cpu)
 97{
 98	return 0;
 99}
100
101extern void ___bad_yield_to_preempted(void);
102static inline void yield_to_preempted(int cpu, u32 yield_count)
103{
104	___bad_yield_to_preempted(); /* This would be a bug */
105}
106
107extern void ___bad_yield_to_any(void);
108static inline void yield_to_any(void)
109{
110	___bad_yield_to_any(); /* This would be a bug */
111}
112
113extern void ___bad_prod_cpu(void);
114static inline void prod_cpu(int cpu)
115{
116	___bad_prod_cpu(); /* This would be a bug */
117}
118
119static inline bool is_vcpu_idle(int vcpu)
120{
121	return false;
122}
123static inline bool vcpu_is_dispatched(int vcpu)
124{
125	return true;
126}
127#endif
128
129#define vcpu_is_preempted vcpu_is_preempted
130static 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
218static inline bool pv_is_native_spin_unlock(void)
219{
220	return !is_shared_processor();
221}
222
223#endif /* _ASM_POWERPC_PARAVIRT_H */