linux-kernel - [PATCH v3 2/3] LoongArch: KVM: Allow to access HW timer CSR registers always

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Date:   Fri, 10 Nov 2023 17:05:28 +0800
From:   Bibo Mao <maobibo@...ngson.cn>
To:     Tianrui Zhao <zhaotianrui@...ngson.cn>,
        Huacai Chen <chenhuacai@...nel.org>
Cc:     WANG Xuerui <kernel@...0n.name>, kvm@...r.kernel.org,
        loongarch@...ts.linux.dev, linux-kernel@...r.kernel.org
Subject: [PATCH v3 2/3] LoongArch: KVM: Allow to access HW timer CSR registers always

Currently HW timer CSR registers are allowed to access before entering to
vm and disabled if switch to SW timer in host mode, instead it is not
necessary to do so. HW timer CSR registers can be accessed always, it
is nothing to do with whether it is in vm mode or host mode. This patch
removes the limitation.

Signed-off-by: Bibo Mao <maobibo@...ngson.cn>
---
 arch/loongarch/kvm/main.c  |  1 -
 arch/loongarch/kvm/timer.c | 27 ++++++---------------------
 2 files changed, 6 insertions(+), 22 deletions(-)

diff --git a/arch/loongarch/kvm/main.c b/arch/loongarch/kvm/main.c
index 1c1d5199500e..86a2f2d0cb27 100644
--- a/arch/loongarch/kvm/main.c
+++ b/arch/loongarch/kvm/main.c
@@ -287,7 +287,6 @@ int kvm_arch_hardware_enable(void)
 	if (env & CSR_GCFG_MATC_ROOT)
 		gcfg |= CSR_GCFG_MATC_ROOT;
 
-	gcfg |= CSR_GCFG_TIT;
 	write_csr_gcfg(gcfg);
 
 	kvm_flush_tlb_all();
diff --git a/arch/loongarch/kvm/timer.c b/arch/loongarch/kvm/timer.c
index 284bf553fefe..1d29bd21a9da 100644
--- a/arch/loongarch/kvm/timer.c
+++ b/arch/loongarch/kvm/timer.c
@@ -70,15 +70,6 @@ void kvm_init_timer(struct kvm_vcpu *vcpu, unsigned long timer_hz)
  */
 void kvm_acquire_timer(struct kvm_vcpu *vcpu)
 {
-	unsigned long cfg;
-
-	cfg = read_csr_gcfg();
-	if (!(cfg & CSR_GCFG_TIT))
-		return;
-
-	/* Enable guest access to hard timer */
-	write_csr_gcfg(cfg & ~CSR_GCFG_TIT);
-
 	/*
 	 * Freeze the soft-timer and sync the guest stable timer with it. We do
 	 * this with interrupts disabled to avoid latency.
@@ -168,21 +159,15 @@ static void _kvm_save_timer(struct kvm_vcpu *vcpu)
  */
 void kvm_save_timer(struct kvm_vcpu *vcpu)
 {
-	unsigned long cfg;
 	struct loongarch_csrs *csr = vcpu->arch.csr;
 
 	preempt_disable();
-	cfg = read_csr_gcfg();
-	if (!(cfg & CSR_GCFG_TIT)) {
-		/* Disable guest use of hard timer */
-		write_csr_gcfg(cfg | CSR_GCFG_TIT);
-
-		/* Save hard timer state */
-		kvm_save_hw_gcsr(csr, LOONGARCH_CSR_TCFG);
-		kvm_save_hw_gcsr(csr, LOONGARCH_CSR_TVAL);
-		if (kvm_read_sw_gcsr(csr, LOONGARCH_CSR_TCFG) & CSR_TCFG_EN)
-			_kvm_save_timer(vcpu);
-	}
+
+	/* Save hard timer state */
+	kvm_save_hw_gcsr(csr, LOONGARCH_CSR_TCFG);
+	kvm_save_hw_gcsr(csr, LOONGARCH_CSR_TVAL);
+	if (kvm_read_sw_gcsr(csr, LOONGARCH_CSR_TCFG) & CSR_TCFG_EN)
+		_kvm_save_timer(vcpu);
 
 	/* Save timer-related state to vCPU context */
 	kvm_save_hw_gcsr(csr, LOONGARCH_CSR_ESTAT);
-- 
2.39.3