linux-kernel - Re: [PATCH v4 2/3] LoongArch: KVM: Allow to access HW timer CSR registers always

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Message-ID: <4b729d67-dd56-6ba2-652c-8d52c3429e35@loongson.cn>
Date:   Mon, 4 Dec 2023 16:48:47 +0800
From:   zhaotianrui <zhaotianrui@...ngson.cn>
To:     Bibo Mao <maobibo@...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: Re: [PATCH v4 2/3] LoongArch: KVM: Allow to access HW timer CSR
 registers always

Reviewed-by: Tianrui Zhao <zhaotianrui@...ngson.cn>

在 2023/11/16 上午10:30, Bibo Mao 写道:
> 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 437e960d8fdb..e37c0ebffabd 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.
> @@ -175,21 +166,15 @@ 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);