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From: guoren@kernel.org
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Cc: linux-riscv@lists.infradead.org,
	linux-kernel@vger.kernel.org,
	kvm@vger.kernel.org,
	virtualization@lists.linux-foundation.org,
	Guo Ren <guoren@linux.alibaba.com>
Subject: [PATCH V12 08/14] riscv: qspinlock: Force virt_spin_lock for KVM guests
Date: Mon, 25 Dec 2023 07:58:41 -0500
Message-Id: <20231225125847.2778638-9-guoren@kernel.org>
In-Reply-To: <20231225125847.2778638-1-guoren@kernel.org>
References: <20231225125847.2778638-1-guoren@kernel.org>
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From: Guo Ren <guoren@linux.alibaba.com>

Force to enable virt_spin_lock when KVM guest, because fair locks
have horrible lock 'holder' preemption issues.

Suggested-by: Leonardo Bras <leobras@redhat.com>
Link: https://lkml.kernel.org/kvm/ZQK9-tn2MepXlY1u@redhat.com/
Signed-off-by: Guo Ren <guoren@linux.alibaba.com>
Signed-off-by: Guo Ren <guoren@kernel.org>
---
 arch/riscv/include/asm/sbi.h | 8 ++++++++
 arch/riscv/kernel/sbi.c      | 2 +-
 arch/riscv/kernel/setup.c    | 6 +++++-
 3 files changed, 14 insertions(+), 2 deletions(-)

diff --git a/arch/riscv/include/asm/sbi.h b/arch/riscv/include/asm/sbi.h
index 0892f4421bc4..8f748d9e1b85 100644
--- a/arch/riscv/include/asm/sbi.h
+++ b/arch/riscv/include/asm/sbi.h
@@ -51,6 +51,13 @@ enum sbi_ext_base_fid {
 	SBI_EXT_BASE_GET_MIMPID,
 };
 
+enum sbi_ext_base_impl_id {
+	SBI_EXT_BASE_IMPL_ID_BBL = 0,
+	SBI_EXT_BASE_IMPL_ID_OPENSBI,
+	SBI_EXT_BASE_IMPL_ID_XVISOR,
+	SBI_EXT_BASE_IMPL_ID_KVM,
+};
+
 enum sbi_ext_time_fid {
 	SBI_EXT_TIME_SET_TIMER = 0,
 };
@@ -276,6 +283,7 @@ int sbi_console_getchar(void);
 long sbi_get_mvendorid(void);
 long sbi_get_marchid(void);
 long sbi_get_mimpid(void);
+long sbi_get_firmware_id(void);
 void sbi_set_timer(uint64_t stime_value);
 void sbi_shutdown(void);
 void sbi_send_ipi(unsigned int cpu);
diff --git a/arch/riscv/kernel/sbi.c b/arch/riscv/kernel/sbi.c
index 5a62ed1da453..4330aedf65fd 100644
--- a/arch/riscv/kernel/sbi.c
+++ b/arch/riscv/kernel/sbi.c
@@ -543,7 +543,7 @@ static inline long sbi_get_spec_version(void)
 	return __sbi_base_ecall(SBI_EXT_BASE_GET_SPEC_VERSION);
 }
 
-static inline long sbi_get_firmware_id(void)
+long sbi_get_firmware_id(void)
 {
 	return __sbi_base_ecall(SBI_EXT_BASE_GET_IMP_ID);
 }
diff --git a/arch/riscv/kernel/setup.c b/arch/riscv/kernel/setup.c
index 0bafb9fd6ea3..e33430e9d97e 100644
--- a/arch/riscv/kernel/setup.c
+++ b/arch/riscv/kernel/setup.c
@@ -281,6 +281,9 @@ DEFINE_STATIC_KEY_TRUE(virt_spin_lock_key);
 
 static void __init virt_spin_lock_init(void)
 {
+	if (sbi_get_firmware_id() != SBI_EXT_BASE_IMPL_ID_KVM)
+		no_virt_spin = true;
+
 	if (no_virt_spin)
 		static_branch_disable(&virt_spin_lock_key);
 	else
@@ -290,7 +293,8 @@ static void __init virt_spin_lock_init(void)
 
 static void __init riscv_spinlock_init(void)
 {
-	if (!enable_qspinlock) {
+	if ((!enable_qspinlock) &&
+	    (sbi_get_firmware_id() != SBI_EXT_BASE_IMPL_ID_KVM)) {
 		static_branch_disable(&combo_qspinlock_key);
 		pr_info("Ticket spinlock: enabled\n");
 	} else {
-- 
2.40.1