In order to produce a generic kernel, a user can select
CONFIG_COMBO_SPINLOCKS which will fallback at runtime to the ticket
spinlock implementation if Zabha or Ziccrse are not present.
Note that we can't use alternatives here because the discovery of
extensions is done too late and we need to start with the qspinlock
implementation because the ticket spinlock implementation would pollute
the spinlock value, so let's use static keys.
This is largely based on Guo's work and Leonardo reviews at [1].
Link: https://lore.kernel.org/linux-riscv/20231225125847.2778638-1-guoren@xxxxxxxxxx/ [1]
Signed-off-by: Guo Ren <guoren@xxxxxxxxxx>
Signed-off-by: Alexandre Ghiti <alexghiti@xxxxxxxxxxxx>
---
.../locking/queued-spinlocks/arch-support.txt | 2 +-
arch/riscv/Kconfig | 29 ++++++++++++++
arch/riscv/include/asm/Kbuild | 4 +-
arch/riscv/include/asm/spinlock.h | 39 +++++++++++++++++++
arch/riscv/kernel/setup.c | 33 ++++++++++++++++
include/asm-generic/qspinlock.h | 2 +
include/asm-generic/ticket_spinlock.h | 2 +
7 files changed, 109 insertions(+), 2 deletions(-)
create mode 100644 arch/riscv/include/asm/spinlock.h
diff --git a/Documentation/features/locking/queued-spinlocks/arch-support.txt b/Documentation/features/locking/queued-spinlocks/arch-support.txt
index 22f2990392ff..cf26042480e2 100644
--- a/Documentation/features/locking/queued-spinlocks/arch-support.txt
+++ b/Documentation/features/locking/queued-spinlocks/arch-support.txt
@@ -20,7 +20,7 @@
| openrisc: | ok |
| parisc: | TODO |
| powerpc: | ok |
- | riscv: | TODO |
+ | riscv: | ok |
| s390: | TODO |
| sh: | TODO |
| sparc: | ok |
diff --git a/arch/riscv/Kconfig b/arch/riscv/Kconfig
index 0bbaec0444d0..5040c7eac70d 100644
--- a/arch/riscv/Kconfig
+++ b/arch/riscv/Kconfig
@@ -72,6 +72,7 @@ config RISCV
select ARCH_WANT_OPTIMIZE_HUGETLB_VMEMMAP
select ARCH_WANTS_NO_INSTR
select ARCH_WANTS_THP_SWAP if HAVE_ARCH_TRANSPARENT_HUGEPAGE
+ select ARCH_WEAK_RELEASE_ACQUIRE if ARCH_USE_QUEUED_SPINLOCKS
select BINFMT_FLAT_NO_DATA_START_OFFSET if !MMU
select BUILDTIME_TABLE_SORT if MMU
select CLINT_TIMER if RISCV_M_MODE
@@ -482,6 +483,34 @@ config NODES_SHIFT
Specify the maximum number of NUMA Nodes available on the target
system. Increases memory reserved to accommodate various tables.
+choice
+ prompt "RISC-V spinlock type"
+ default RISCV_COMBO_SPINLOCKS
+
+config RISCV_TICKET_SPINLOCKS
+ bool "Using ticket spinlock"
+
+config RISCV_QUEUED_SPINLOCKS
+ bool "Using queued spinlock"
+ depends on SMP && MMU
+ select ARCH_USE_QUEUED_SPINLOCKS
+ help
+ The queued spinlock implementation requires the forward progress
+ guarantee of cmpxchg()/xchg() atomic operations: CAS with Zabha or
+ LR/SC with Ziccrse provide such guarantee.
+
+ Select this if and only if Zabha or Ziccrse is available on your
+ platform.
+
+config RISCV_COMBO_SPINLOCKS
+ bool "Using combo spinlock"
+ depends on SMP && MMU
+ select ARCH_USE_QUEUED_SPINLOCKS
+ help
+ Embed both queued spinlock and ticket lock so that the spinlock
+ implementation can be chosen at runtime.
+endchoice
+
config RISCV_ALTERNATIVE
bool
depends on !XIP_KERNEL
diff --git a/arch/riscv/include/asm/Kbuild b/arch/riscv/include/asm/Kbuild
index 504f8b7e72d4..ad72f2bd4cc9 100644
--- a/arch/riscv/include/asm/Kbuild
+++ b/arch/riscv/include/asm/Kbuild
@@ -2,10 +2,12 @@
generic-y += early_ioremap.h
generic-y += flat.h
generic-y += kvm_para.h
+generic-y += mcs_spinlock.h
generic-y += parport.h
-generic-y += spinlock.h
generic-y += spinlock_types.h
+generic-y += ticket_spinlock.h
generic-y += qrwlock.h
generic-y += qrwlock_types.h
+generic-y += qspinlock.h
generic-y += user.h
generic-y += vmlinux.lds.h
diff --git a/arch/riscv/include/asm/spinlock.h b/arch/riscv/include/asm/spinlock.h
new file mode 100644
index 000000000000..4856d50006f2
--- /dev/null
+++ b/arch/riscv/include/asm/spinlock.h
@@ -0,0 +1,39 @@
+/* SPDX-License-Identifier: GPL-2.0 */
+
+#ifndef __ASM_RISCV_SPINLOCK_H
+#define __ASM_RISCV_SPINLOCK_H
+
+#ifdef CONFIG_RISCV_COMBO_SPINLOCKS
+#define _Q_PENDING_LOOPS (1 << 9)
+
+#define __no_arch_spinlock_redefine
+#include <asm/ticket_spinlock.h>
+#include <asm/qspinlock.h>
+#include <asm/alternative.h>
+
+DECLARE_STATIC_KEY_TRUE(qspinlock_key);
+
+#define SPINLOCK_BASE_DECLARE(op, type, type_lock) \
+static __always_inline type arch_spin_##op(type_lock lock) \
+{ \
+ if (static_branch_unlikely(&qspinlock_key)) \
+ return queued_spin_##op(lock); \
+ return ticket_spin_##op(lock); \
+}
+
+SPINLOCK_BASE_DECLARE(lock, void, arch_spinlock_t *)
+SPINLOCK_BASE_DECLARE(unlock, void, arch_spinlock_t *)
+SPINLOCK_BASE_DECLARE(is_locked, int, arch_spinlock_t *)
+SPINLOCK_BASE_DECLARE(is_contended, int, arch_spinlock_t *)
+SPINLOCK_BASE_DECLARE(trylock, bool, arch_spinlock_t *)
+SPINLOCK_BASE_DECLARE(value_unlocked, int, arch_spinlock_t)
+
+#else
+
+#include <asm/ticket_spinlock.h>
+
+#endif
+
+#include <asm/qrwlock.h>
+
+#endif /* __ASM_RISCV_SPINLOCK_H */
diff --git a/arch/riscv/kernel/setup.c b/arch/riscv/kernel/setup.c
index 4f73c0ae44b2..d7c31c9b8ead 100644
--- a/arch/riscv/kernel/setup.c
+++ b/arch/riscv/kernel/setup.c
@@ -244,6 +244,38 @@ static void __init parse_dtb(void)
#endif
}
+DEFINE_STATIC_KEY_TRUE(qspinlock_key);
+EXPORT_SYMBOL(qspinlock_key);
+
+static void __init riscv_spinlock_init(void)
+{
+ char *using_ext;
+
+ if (IS_ENABLED(CONFIG_RISCV_ISA_ZACAS) &&
+ IS_ENABLED(CONFIG_RISCV_ISA_ZABHA)) {
+ using_ext = "using Zabha";
+
+ asm goto(ALTERNATIVE("j %[no_zacas]", "nop", 0, RISCV_ISA_EXT_ZACAS, 1)
+ : : : : no_zacas);
+ asm goto(ALTERNATIVE("nop", "j %[qspinlock]", 0, RISCV_ISA_EXT_ZABHA, 1)
+ : : : : qspinlock);
+ }
