Re: [PATCH 03/13] RISC-V: KVM: Save/restore SCOUNTEREN in C source

Atish Patra
2024-10-16T21:36:59Z

On Fri, Jul 19, 2024 at 9:09 AM Anup Patel <apatel@ventanamicro.com> wrote:
>
> The SCOUNTEREN CSR need not be saved/restored in the low-level
> __kvm_riscv_switch_to() function hence move the SCOUNTEREN CSR
> save/restore to the kvm_riscv_vcpu_swap_in_guest_state() and
> kvm_riscv_vcpu_swap_in_host_state() functions in C sources.
>
> Also, re-arrange the CSR save/restore and related GPR usage in
> the low-level __kvm_riscv_switch_to() low-level function.
>
> Signed-off-by: Anup Patel <apatel@ventanamicro.com>
> ---
> arch/riscv/kvm/vcpu.c | 2 ++
> arch/riscv/kvm/vcpu_switch.S | 52 +++++++++++++++---------------------
> 2 files changed, 23 insertions(+), 31 deletions(-)
>
> diff --git a/arch/riscv/kvm/vcpu.c b/arch/riscv/kvm/vcpu.c
> index 93b1ce043482..957e1a5e081b 100644
> --- a/arch/riscv/kvm/vcpu.c
> +++ b/arch/riscv/kvm/vcpu.c
> @@ -691,6 +691,7 @@ static __always_inline void kvm_riscv_vcpu_swap_in_guest_state(struct kvm_vcpu *
> struct kvm_vcpu_csr *csr = &vcpu->arch.guest_csr;
> struct kvm_vcpu_config *cfg = &vcpu->arch.cfg;
>
> + vcpu->arch.host_scounteren = csr_swap(CSR_SCOUNTEREN, csr->scounteren);
> vcpu->arch.host_senvcfg = csr_swap(CSR_SENVCFG, csr->senvcfg);
> if (riscv_has_extension_unlikely(RISCV_ISA_EXT_SMSTATEEN) &&
> (cfg->hstateen0 & SMSTATEEN0_SSTATEEN0))
> @@ -704,6 +705,7 @@ static __always_inline void kvm_riscv_vcpu_swap_in_host_state(struct kvm_vcpu *v
> struct kvm_vcpu_csr *csr = &vcpu->arch.guest_csr;
> struct kvm_vcpu_config *cfg = &vcpu->arch.cfg;
>
> + csr->scounteren = csr_swap(CSR_SCOUNTEREN, vcpu->arch.host_scounteren);
> csr->senvcfg = csr_swap(CSR_SENVCFG, vcpu->arch.host_senvcfg);
> if (riscv_has_extension_unlikely(RISCV_ISA_EXT_SMSTATEEN) &&
> (cfg->hstateen0 & SMSTATEEN0_SSTATEEN0))
> diff --git a/arch/riscv/kvm/vcpu_switch.S b/arch/riscv/kvm/vcpu_switch.S
> index f83643c4fdb9..3f8cbc21a644 100644
> --- a/arch/riscv/kvm/vcpu_switch.S
> +++ b/arch/riscv/kvm/vcpu_switch.S
> @@ -43,30 +43,25 @@ 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_SCOUNTEREN)(a0)
> - la t3, .Lkvm_switch_return
> - REG_L t4, (KVM_ARCH_GUEST_SEPC)(a0)
> + la t1, .Lkvm_switch_return
> + REG_L t2, (KVM_ARCH_GUEST_SEPC)(a0)
>
> /* Save Host and Restore Guest SSTATUS */
> csrrw t0, CSR_SSTATUS, t0
>
> - /* Save Host and Restore Guest SCOUNTEREN */
> - csrrw t1, CSR_SCOUNTEREN, t1
> -
> /* Save Host STVEC and change it to return path */
> - csrrw t3, CSR_STVEC, t3
> -
> - /* Save Host SSCRATCH and change it to struct kvm_vcpu_arch pointer */
> - csrrw t2, CSR_SSCRATCH, a0
> + csrrw t1, CSR_STVEC, t1
>
> /* Restore Guest SEPC */
> - csrw CSR_SEPC, t4
> + csrw CSR_SEPC, t2
> +
> + /* Save Host SSCRATCH and change it to struct kvm_vcpu_arch pointer */
> + csrrw t3, CSR_SSCRATCH, a0
>
> /* Store Host CSR values */
> REG_S t0, (KVM_ARCH_HOST_SSTATUS)(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)
> + REG_S t1, (KVM_ARCH_HOST_STVEC)(a0)
> + REG_S t3, (KVM_ARCH_HOST_SSCRATCH)(a0)
>
> /* Restore Guest GPRs (except A0) */
> REG_L ra, (KVM_ARCH_GUEST_RA)(a0)
> @@ -145,31 +140,26 @@ SYM_FUNC_START(__kvm_riscv_switch_to)
> REG_S t6, (KVM_ARCH_GUEST_T6)(a0)
>
> /* Load Host CSR values */
> - 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_SSTATUS)(a0)
> -
> - /* Save Guest SEPC */
> - csrr t0, CSR_SEPC
> + REG_L t0, (KVM_ARCH_HOST_STVEC)(a0)
> + REG_L t1, (KVM_ARCH_HOST_SSCRATCH)(a0)
> + REG_L t2, (KVM_ARCH_HOST_SSTATUS)(a0)
>
> /* Save Guest A0 and Restore Host SSCRATCH */
> - csrrw t2, CSR_SSCRATCH, t2
> + csrrw t1, CSR_SSCRATCH, t1
>
> - /* Restore Host STVEC */
> - csrw CSR_STVEC, t1
> + /* Save Guest SEPC */
> + csrr t3, CSR_SEPC
>
> - /* Save Guest and Restore Host SCOUNTEREN */
> - csrrw t3, CSR_SCOUNTEREN, t3
> + /* Restore Host STVEC */
> + csrw CSR_STVEC, t0
>
> /* Save Guest and Restore Host SSTATUS */
> - csrrw t4, CSR_SSTATUS, t4
> + csrrw t2, CSR_SSTATUS, t2
>
> /* 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_SSTATUS)(a0)
> + REG_S t1, (KVM_ARCH_GUEST_A0)(a0)
> + REG_S t2, (KVM_ARCH_GUEST_SSTATUS)(a0)
> + REG_S t3, (KVM_ARCH_GUEST_SEPC)(a0)
>
> /* Restore Host GPRs (except A0 and T0-T6) */
> REG_L ra, (KVM_ARCH_HOST_RA)(a0)
> --
> 2.34.1
>

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

--
Regards,
Atish