153 lines
4.4 KiB
C
153 lines
4.4 KiB
C
/* SPDX-License-Identifier: GPL-2.0-or-later */
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#ifndef _ASM_POWERPC_PARAVIRT_H
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#define _ASM_POWERPC_PARAVIRT_H
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#include <linux/jump_label.h>
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#include <asm/smp.h>
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#ifdef CONFIG_PPC64
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#include <asm/paca.h>
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#include <asm/hvcall.h>
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#endif
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#ifdef CONFIG_PPC_SPLPAR
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#include <linux/smp.h>
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#include <asm/kvm_guest.h>
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#include <asm/cputhreads.h>
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DECLARE_STATIC_KEY_FALSE(shared_processor);
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static inline bool is_shared_processor(void)
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{
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return static_branch_unlikely(&shared_processor);
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}
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/* If bit 0 is set, the cpu has been ceded, conferred, or preempted */
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static inline u32 yield_count_of(int cpu)
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{
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__be32 yield_count = READ_ONCE(lppaca_of(cpu).yield_count);
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return be32_to_cpu(yield_count);
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}
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/*
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* Spinlock code confers and prods, so don't trace the hcalls because the
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* tracing code takes spinlocks which can cause recursion deadlocks.
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*
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* These calls are made while the lock is not held: the lock slowpath yields if
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* it can not acquire the lock, and unlock slow path might prod if a waiter has
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* yielded). So this may not be a problem for simple spin locks because the
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* tracing does not technically recurse on the lock, but we avoid it anyway.
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*
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* However the queued spin lock contended path is more strictly ordered: the
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* H_CONFER hcall is made after the task has queued itself on the lock, so then
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* recursing on that lock will cause the task to then queue up again behind the
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* first instance (or worse: queued spinlocks use tricks that assume a context
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* never waits on more than one spinlock, so such recursion may cause random
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* corruption in the lock code).
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*/
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static inline void yield_to_preempted(int cpu, u32 yield_count)
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{
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plpar_hcall_norets_notrace(H_CONFER, get_hard_smp_processor_id(cpu), yield_count);
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}
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static inline void prod_cpu(int cpu)
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{
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plpar_hcall_norets_notrace(H_PROD, get_hard_smp_processor_id(cpu));
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}
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static inline void yield_to_any(void)
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{
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plpar_hcall_norets_notrace(H_CONFER, -1, 0);
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}
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#else
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static inline bool is_shared_processor(void)
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{
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return false;
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}
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static inline u32 yield_count_of(int cpu)
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{
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return 0;
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}
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extern void ___bad_yield_to_preempted(void);
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static inline void yield_to_preempted(int cpu, u32 yield_count)
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{
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___bad_yield_to_preempted(); /* This would be a bug */
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}
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extern void ___bad_yield_to_any(void);
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static inline void yield_to_any(void)
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{
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___bad_yield_to_any(); /* This would be a bug */
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}
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extern void ___bad_prod_cpu(void);
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static inline void prod_cpu(int cpu)
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{
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___bad_prod_cpu(); /* This would be a bug */
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}
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#endif
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#define vcpu_is_preempted vcpu_is_preempted
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static inline bool vcpu_is_preempted(int cpu)
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{
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/*
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* The dispatch/yield bit alone is an imperfect indicator of
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* whether the hypervisor has dispatched @cpu to run on a physical
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* processor. When it is clear, @cpu is definitely not preempted.
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* But when it is set, it means only that it *might* be, subject to
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* other conditions. So we check other properties of the VM and
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* @cpu first, resorting to the yield count last.
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*/
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/*
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* Hypervisor preemption isn't possible in dedicated processor
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* mode by definition.
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*/
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if (!is_shared_processor())
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return false;
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#ifdef CONFIG_PPC_SPLPAR
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if (!is_kvm_guest()) {
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int first_cpu;
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/*
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* The result of vcpu_is_preempted() is used in a
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* speculative way, and is always subject to invalidation
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* by events internal and external to Linux. While we can
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* be called in preemptable context (in the Linux sense),
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* we're not accessing per-cpu resources in a way that can
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* race destructively with Linux scheduler preemption and
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* migration, and callers can tolerate the potential for
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* error introduced by sampling the CPU index without
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* pinning the task to it. So it is permissible to use
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* raw_smp_processor_id() here to defeat the preempt debug
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* warnings that can arise from using smp_processor_id()
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* in arbitrary contexts.
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*/
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first_cpu = cpu_first_thread_sibling(raw_smp_processor_id());
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/*
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* The PowerVM hypervisor dispatches VMs on a whole core
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* basis. So we know that a thread sibling of the local CPU
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* cannot have been preempted by the hypervisor, even if it
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* has called H_CONFER, which will set the yield bit.
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*/
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if (cpu_first_thread_sibling(cpu) == first_cpu)
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return false;
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}
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#endif
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if (yield_count_of(cpu) & 1)
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return true;
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return false;
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}
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static inline bool pv_is_native_spin_unlock(void)
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{
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return !is_shared_processor();
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}
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#endif /* _ASM_POWERPC_PARAVIRT_H */
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