1 /* SPDX-License-Identifier: GPL-2.0-only */
2 /*
3  * A stand-alone ticket spinlock implementation for use by the non-VHE
4  * KVM hypervisor code running at EL2.
5  *
6  * Copyright (C) 2020 Google LLC
7  * Author: Will Deacon <will@kernel.org>
8  *
9  * Heavily based on the implementation removed by c11090474d70 which was:
10  * Copyright (C) 2012 ARM Ltd.
11  */
12 
13 #ifndef __ARM64_KVM_NVHE_SPINLOCK_H__
14 #define __ARM64_KVM_NVHE_SPINLOCK_H__
15 
16 #include <asm/alternative.h>
17 #include <asm/lse.h>
18 #include <asm/rwonce.h>
19 
20 typedef union hyp_spinlock {
21 	u32	__val;
22 	struct {
23 #ifdef __AARCH64EB__
24 		u16 next, owner;
25 #else
26 		u16 owner, next;
27 #endif
28 	};
29 } hyp_spinlock_t;
30 
31 #define hyp_spin_lock_init(l)						\
32 do {									\
33 	*(l) = (hyp_spinlock_t){ .__val = 0 };				\
34 } while (0)
35 
36 static inline void hyp_spin_lock(hyp_spinlock_t *lock)
37 {
38 	u32 tmp;
39 	hyp_spinlock_t lockval, newval;
40 
41 	asm volatile(
42 	/* Atomically increment the next ticket. */
43 	ARM64_LSE_ATOMIC_INSN(
44 	/* LL/SC */
45 "	prfm	pstl1strm, %3\n"
46 "1:	ldaxr	%w0, %3\n"
47 "	add	%w1, %w0, #(1 << 16)\n"
48 "	stxr	%w2, %w1, %3\n"
49 "	cbnz	%w2, 1b\n",
50 	/* LSE atomics */
51 "	mov	%w2, #(1 << 16)\n"
52 "	ldadda	%w2, %w0, %3\n"
53 	__nops(3))
54 
55 	/* Did we get the lock? */
56 "	eor	%w1, %w0, %w0, ror #16\n"
57 "	cbz	%w1, 3f\n"
58 	/*
59 	 * No: spin on the owner. Send a local event to avoid missing an
60 	 * unlock before the exclusive load.
61 	 */
62 "	sevl\n"
63 "2:	wfe\n"
64 "	ldaxrh	%w2, %4\n"
65 "	eor	%w1, %w2, %w0, lsr #16\n"
66 "	cbnz	%w1, 2b\n"
67 	/* We got the lock. Critical section starts here. */
68 "3:"
69 	: "=&r" (lockval), "=&r" (newval), "=&r" (tmp), "+Q" (*lock)
70 	: "Q" (lock->owner)
71 	: "memory");
72 }
73 
74 static inline void hyp_spin_unlock(hyp_spinlock_t *lock)
75 {
76 	u64 tmp;
77 
78 	asm volatile(
79 	ARM64_LSE_ATOMIC_INSN(
80 	/* LL/SC */
81 	"	ldrh	%w1, %0\n"
82 	"	add	%w1, %w1, #1\n"
83 	"	stlrh	%w1, %0",
84 	/* LSE atomics */
85 	"	mov	%w1, #1\n"
86 	"	staddlh	%w1, %0\n"
87 	__nops(1))
88 	: "=Q" (lock->owner), "=&r" (tmp)
89 	:
90 	: "memory");
91 }
92 
93 static inline bool hyp_spin_is_locked(hyp_spinlock_t *lock)
94 {
95 	hyp_spinlock_t lockval = READ_ONCE(*lock);
96 
97 	return lockval.owner != lockval.next;
98 }
99 
100 #ifdef CONFIG_NVHE_EL2_DEBUG
101 static inline void hyp_assert_lock_held(hyp_spinlock_t *lock)
102 {
103 	/*
104 	 * The __pkvm_init() path accesses protected data-structures without
105 	 * holding locks as the other CPUs are guaranteed to not enter EL2
106 	 * concurrently at this point in time. The point by which EL2 is
107 	 * initialized on all CPUs is reflected in the pkvm static key, so
108 	 * wait until it is set before checking the lock state.
109 	 */
110 	if (static_branch_likely(&kvm_protected_mode_initialized))
111 		BUG_ON(!hyp_spin_is_locked(lock));
112 }
113 #else
114 static inline void hyp_assert_lock_held(hyp_spinlock_t *lock) { }
115 #endif
116 
117 #endif /* __ARM64_KVM_NVHE_SPINLOCK_H__ */
118