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FROMLIST: arm64: kvm: Add standalone ticket spinlock implementation for use at hyp

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We will soon need to synchronise multiple CPUs in the hyp text at EL2.
The qspinlock-based locking used by the host is overkill for this purpose
and relies on the kernel's "percpu" implementation for the MCS nodes.

Implement a simple ticket locking scheme based heavily on the code removed
by commit c11090474d ("arm64: locking: Replace ticket lock implementation
with qspinlock").

Signed-off-by: Will Deacon <will@kernel.org>
Signed-off-by: Quentin Perret <qperret@google.com>
Link: https://lore.kernel.org/r/20210315143536.214621-4-qperret@google.com
Bug: 178098380
Change-Id: Iecc108a89c71689ba281bf3e15dd0b1015595f1a
This commit is contained in:
Will Deacon
2021-03-15 14:35:03 +00:00
committed by Quentin Perret
parent 9833905e2d
commit ce5e848201
1 changed files with 92 additions and 0 deletions
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92
arch/arm64/kvm/hyp/include/nvhe/spinlock.h Normal file
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/* SPDX-License-Identifier: GPL-2.0-only */
/*
* A stand-alone ticket spinlock implementation for use by the non-VHE
* KVM hypervisor code running at EL2.
*
* Copyright (C) 2020 Google LLC
* Author: Will Deacon <will@kernel.org>
*
* Heavily based on the implementation removed by c11090474d70 which was:
* Copyright (C) 2012 ARM Ltd.
*/
#ifndef __ARM64_KVM_NVHE_SPINLOCK_H__
#define __ARM64_KVM_NVHE_SPINLOCK_H__
#include <asm/alternative.h>
#include <asm/lse.h>
typedef union hyp_spinlock {
u32 __val;
struct {
#ifdef __AARCH64EB__
u16 next, owner;
#else
u16 owner, next;
#endif
};
} hyp_spinlock_t;
#define hyp_spin_lock_init(l) \
do { \
*(l) = (hyp_spinlock_t){ .__val = 0 }; \
} while (0)
static inline void hyp_spin_lock(hyp_spinlock_t *lock)
{
u32 tmp;
hyp_spinlock_t lockval, newval;
asm volatile(
/* Atomically increment the next ticket. */
ARM64_LSE_ATOMIC_INSN(
/* LL/SC */
" prfm pstl1strm, %3\n"
"1: ldaxr %w0, %3\n"
" add %w1, %w0, #(1 << 16)\n"
" stxr %w2, %w1, %3\n"
" cbnz %w2, 1b\n",
/* LSE atomics */
" mov %w2, #(1 << 16)\n"
" ldadda %w2, %w0, %3\n"
__nops(3))
/* Did we get the lock? */
" eor %w1, %w0, %w0, ror #16\n"
" cbz %w1, 3f\n"
/*
* No: spin on the owner. Send a local event to avoid missing an
* unlock before the exclusive load.
*/
" sevl\n"
"2: wfe\n"
" ldaxrh %w2, %4\n"
" eor %w1, %w2, %w0, lsr #16\n"
" cbnz %w1, 2b\n"
/* We got the lock. Critical section starts here. */
"3:"
: "=&r" (lockval), "=&r" (newval), "=&r" (tmp), "+Q" (*lock)
: "Q" (lock->owner)
: "memory");
}
static inline void hyp_spin_unlock(hyp_spinlock_t *lock)
{
u64 tmp;
asm volatile(
ARM64_LSE_ATOMIC_INSN(
/* LL/SC */
" ldrh %w1, %0\n"
" add %w1, %w1, #1\n"
" stlrh %w1, %0",
/* LSE atomics */
" mov %w1, #1\n"
" staddlh %w1, %0\n"
__nops(1))
: "=Q" (lock->owner), "=&r" (tmp)
:
: "memory");
}
#endif /* __ARM64_KVM_NVHE_SPINLOCK_H__ */