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