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

Atish Patra
2024-10-16T19:27:41Z

> 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@ventanamicro.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@rivosinc.com>