Commit ecbd8047 authored by Kumar Kartikeya Dwivedi's avatar Kumar Kartikeya Dwivedi Committed by Alexei Starovoitov
Browse files

rqspinlock: Add basic support for CONFIG_PARAVIRT 



We ripped out PV and virtualization related bits from rqspinlock in an
earlier commit, however, a fair lock performs poorly within a virtual
machine when the lock holder is preempted. As such, retain the
virt_spin_lock fallback to test and set lock, but with timeout and
deadlock detection. We can do this by simply depending on the
resilient_tas_spin_lock implementation from the previous patch.

We don't integrate support for CONFIG_PARAVIRT_SPINLOCKS yet, as that
requires more involved algorithmic changes and introduces more
complexity. It can be done when the need arises in the future.

Signed-off-by: default avatarKumar Kartikeya Dwivedi <memxor@gmail.com>
Link: https://lore.kernel.org/r/20250316040541.108729-15-memxor@gmail.com


Signed-off-by: default avatarAlexei Starovoitov <ast@kernel.org>
parent c9102a68

arch/x86/include/asm/rqspinlock.h

0 → 100644
+33 −0
Original line number Diff line number Diff line 
/* SPDX-License-Identifier: GPL-2.0 */

#ifndef _ASM_X86_RQSPINLOCK_H

#define _ASM_X86_RQSPINLOCK_H



#include <asm/paravirt.h>



#ifdef CONFIG_PARAVIRT

DECLARE_STATIC_KEY_FALSE(virt_spin_lock_key);



#define resilient_virt_spin_lock_enabled resilient_virt_spin_lock_enabled

static __always_inline bool resilient_virt_spin_lock_enabled(void)

{

       return static_branch_likely(&virt_spin_lock_key);

}



#ifdef CONFIG_QUEUED_SPINLOCKS

typedef struct qspinlock rqspinlock_t;

#else

typedef struct rqspinlock rqspinlock_t;

#endif

extern int resilient_tas_spin_lock(rqspinlock_t *lock);



#define resilient_virt_spin_lock resilient_virt_spin_lock

static inline int resilient_virt_spin_lock(rqspinlock_t *lock)

{

	return resilient_tas_spin_lock(lock);

}



#endif /* CONFIG_PARAVIRT */



#include <asm-generic/rqspinlock.h>



#endif /* _ASM_X86_RQSPINLOCK_H */

include/asm-generic/rqspinlock.h

+14 −0
Original line number Diff line number Diff line
@@ -35,6 +35,20 @@ extern int resilient_tas_spin_lock(rqspinlock_t *lock); 
extern int resilient_queued_spin_lock_slowpath(rqspinlock_t *lock, u32 val);

#endif



#ifndef resilient_virt_spin_lock_enabled

static __always_inline bool resilient_virt_spin_lock_enabled(void)

{

	return false;

}

#endif



#ifndef resilient_virt_spin_lock

static __always_inline int resilient_virt_spin_lock(rqspinlock_t *lock)

{

	return 0;

}

#endif



/*

 * Default timeout for waiting loops is 0.25 seconds

 */

kernel/bpf/rqspinlock.c

+3 −0
Original line number Diff line number Diff line
@@ -352,6 +352,9 @@ int __lockfunc resilient_queued_spin_lock_slowpath(rqspinlock_t *lock, u32 val) 


	BUILD_BUG_ON(CONFIG_NR_CPUS >= (1U << _Q_TAIL_CPU_BITS));



	if (resilient_virt_spin_lock_enabled())

		return resilient_virt_spin_lock(lock);



	RES_INIT_TIMEOUT(ts);



	/*