On Monday 01 Feb 2021 at 17:28:34 (+0000), Will Deacon wrote:

On Fri, Jan 08, 2021 at 12:15:01PM +0000, Quentin Perret wrote:

quoted

From: Will Deacon <will@kernel.org>

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 c11090474d70 ("arm64: locking: Replace ticket lock implementation
with qspinlock").

Signed-off-by: Will Deacon <will@kernel.org>
Signed-off-by: Quentin Perret <redacted>
---
 arch/arm64/kvm/hyp/include/nvhe/spinlock.h | 92 ++++++++++++++++++++++
 1 file changed, 92 insertions(+)
 create mode 100644 arch/arm64/kvm/hyp/include/nvhe/spinlock.h

diff --git a/arch/arm64/kvm/hyp/include/nvhe/spinlock.h b/arch/arm64/kvm/hyp/include/nvhe/spinlock.h
new file mode 100644
index 000000000000..7584c397bbac
--- /dev/null
+++ b/arch/arm64/kvm/hyp/include/nvhe/spinlock.h

@@ -0,0 +1,92 @@
+/* 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

Looks like I put this #endif in the wrong place; probably needs to be a line
higher.

Uh oh, missed that too. Fix now merged locally, thanks.

Quentin