linux-kernel - Re: [02/13] RISC-V: KVM: Save/restore HSTATUS in C source

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Message-Id: <20241016192738.646447-1-atishp@rivosinc.com>
Date: Wed, 16 Oct 2024 12:27:38 -0700
From: Atish Patra <atishp@...osinc.com>
To: apatel@...tanamicro.com
Cc: Palmer Dabbelt <palmer@...belt.com>,
	Paul Walmsley <paul.walmsley@...ive.com>,
	Atish Patra <atishp@...shpatra.org>,
	Andrew Jones <ajones@...tanamicro.com>,
	Anup Patel <anup@...infault.org>,
	kvm@...r.kernel.org,
	kvm-riscv@...ts.infradead.org,
	linux-riscv@...ts.infradead.org,
	linux-kernel@...r.kernel.org,
	Atish Patra <atishp@...osinc.com>
Subject: Re: [02/13] RISC-V: KVM: Save/restore HSTATUS in C source

> We will be optimizing HSTATUS CSR access via shared memory setup
> using the SBI nested acceleration extension. To facilitate this,
> we first move HSTATUS save/restore in kvm_riscv_vcpu_enter_exit().
> 
> Signed-off-by: Anup Patel <apatel@...tanamicro.com>
> ---
>  arch/riscv/kvm/vcpu.c        |  9 +++++++++
>  arch/riscv/kvm/vcpu_switch.S | 36 +++++++++++++-----------------------
>  2 files changed, 22 insertions(+), 23 deletions(-)
> diff --git a/arch/riscv/kvm/vcpu.c b/arch/riscv/kvm/vcpu.c
> index 449e5bb948c2..93b1ce043482 100644
> --- a/arch/riscv/kvm/vcpu.c
> +++ b/arch/riscv/kvm/vcpu.c
> @@ -720,9 +720,18 @@ static __always_inline void kvm_riscv_vcpu_swap_in_host_state(struct kvm_vcpu *v
>   */
>  static void noinstr kvm_riscv_vcpu_enter_exit(struct kvm_vcpu *vcpu)
>  {
> +	struct kvm_cpu_context *gcntx = &vcpu->arch.guest_context;
> +	struct kvm_cpu_context *hcntx = &vcpu->arch.host_context;
> +
>  	kvm_riscv_vcpu_swap_in_guest_state(vcpu);
>  	guest_state_enter_irqoff();
> +
> +	hcntx->hstatus = csr_swap(CSR_HSTATUS, gcntx->hstatus);
> +
>  	__kvm_riscv_switch_to(&vcpu->arch);
> +
> +	gcntx->hstatus = csr_swap(CSR_HSTATUS, hcntx->hstatus);
> +
>  	vcpu->arch.last_exit_cpu = vcpu->cpu;
>  	guest_state_exit_irqoff();
>  	kvm_riscv_vcpu_swap_in_host_state(vcpu);
> diff --git a/arch/riscv/kvm/vcpu_switch.S b/arch/riscv/kvm/vcpu_switch.S
> index 0c26189aa01c..f83643c4fdb9 100644
> --- a/arch/riscv/kvm/vcpu_switch.S
> +++ b/arch/riscv/kvm/vcpu_switch.S
> @@ -43,35 +43,30 @@ SYM_FUNC_START(__kvm_riscv_switch_to)
>  
>  	/* Load Guest CSR values */
>  	REG_L	t0, (KVM_ARCH_GUEST_SSTATUS)(a0)
> -	REG_L	t1, (KVM_ARCH_GUEST_HSTATUS)(a0)
> -	REG_L	t2, (KVM_ARCH_GUEST_SCOUNTEREN)(a0)
> -	la	t4, .Lkvm_switch_return
> -	REG_L	t5, (KVM_ARCH_GUEST_SEPC)(a0)
> +	REG_L	t1, (KVM_ARCH_GUEST_SCOUNTEREN)(a0)
> +	la	t3, .Lkvm_switch_return
> +	REG_L	t4, (KVM_ARCH_GUEST_SEPC)(a0)
>  
>  	/* Save Host and Restore Guest SSTATUS */
>  	csrrw	t0, CSR_SSTATUS, t0
>  
> -	/* Save Host and Restore Guest HSTATUS */
> -	csrrw	t1, CSR_HSTATUS, t1
> -
>  	/* Save Host and Restore Guest SCOUNTEREN */
> -	csrrw	t2, CSR_SCOUNTEREN, t2
> +	csrrw	t1, CSR_SCOUNTEREN, t1
>  
>  	/* Save Host STVEC and change it to return path */
> -	csrrw	t4, CSR_STVEC, t4
> +	csrrw	t3, CSR_STVEC, t3
>  
>  	/* Save Host SSCRATCH and change it to struct kvm_vcpu_arch pointer */
> -	csrrw	t3, CSR_SSCRATCH, a0
> +	csrrw	t2, CSR_SSCRATCH, a0
>  
>  	/* Restore Guest SEPC */
> -	csrw	CSR_SEPC, t5
> +	csrw	CSR_SEPC, t4
>  
>  	/* Store Host CSR values */
>  	REG_S	t0, (KVM_ARCH_HOST_SSTATUS)(a0)
> -	REG_S	t1, (KVM_ARCH_HOST_HSTATUS)(a0)
> -	REG_S	t2, (KVM_ARCH_HOST_SCOUNTEREN)(a0)
> -	REG_S	t3, (KVM_ARCH_HOST_SSCRATCH)(a0)
> -	REG_S	t4, (KVM_ARCH_HOST_STVEC)(a0)
> +	REG_S	t1, (KVM_ARCH_HOST_SCOUNTEREN)(a0)
> +	REG_S	t2, (KVM_ARCH_HOST_SSCRATCH)(a0)
> +	REG_S	t3, (KVM_ARCH_HOST_STVEC)(a0)
>  
>  	/* Restore Guest GPRs (except A0) */
>  	REG_L	ra, (KVM_ARCH_GUEST_RA)(a0)
> @@ -153,8 +148,7 @@ SYM_FUNC_START(__kvm_riscv_switch_to)
>  	REG_L	t1, (KVM_ARCH_HOST_STVEC)(a0)
>  	REG_L	t2, (KVM_ARCH_HOST_SSCRATCH)(a0)
>  	REG_L	t3, (KVM_ARCH_HOST_SCOUNTEREN)(a0)
> -	REG_L	t4, (KVM_ARCH_HOST_HSTATUS)(a0)
> -	REG_L	t5, (KVM_ARCH_HOST_SSTATUS)(a0)
> +	REG_L	t4, (KVM_ARCH_HOST_SSTATUS)(a0)
>  
>  	/* Save Guest SEPC */
>  	csrr	t0, CSR_SEPC
> @@ -168,18 +162,14 @@ SYM_FUNC_START(__kvm_riscv_switch_to)
>  	/* Save Guest and Restore Host SCOUNTEREN */
>  	csrrw	t3, CSR_SCOUNTEREN, t3
>  
> -	/* Save Guest and Restore Host HSTATUS */
> -	csrrw	t4, CSR_HSTATUS, t4
> -
>  	/* Save Guest and Restore Host SSTATUS */
> -	csrrw	t5, CSR_SSTATUS, t5
> +	csrrw	t4, CSR_SSTATUS, t4
>  
>  	/* Store Guest CSR values */
>  	REG_S	t0, (KVM_ARCH_GUEST_SEPC)(a0)
>  	REG_S	t2, (KVM_ARCH_GUEST_A0)(a0)
>  	REG_S	t3, (KVM_ARCH_GUEST_SCOUNTEREN)(a0)
> -	REG_S	t4, (KVM_ARCH_GUEST_HSTATUS)(a0)
> -	REG_S	t5, (KVM_ARCH_GUEST_SSTATUS)(a0)
> +	REG_S	t4, (KVM_ARCH_GUEST_SSTATUS)(a0)
>  
>  	/* Restore Host GPRs (except A0 and T0-T6) */
>  	REG_L	ra, (KVM_ARCH_HOST_RA)(a0)
>

Reviewed-by: Atish Patra <atishp@...osinc.com>