Re: [PATCH 12/13] RISC-V: KVM: Save trap CSRs in kvm_riscv_vcpu_enter_exit()

Atish Patra
2024-10-18T20:11:31Z

On Fri, Jul 19, 2024 at 9:10 AM Anup Patel <apatel@ventanamicro.com> wrote:
>
> Save trap CSRs in the kvm_riscv_vcpu_enter_exit() function instead of
> the kvm_arch_vcpu_ioctl_run() function so that HTVAL and HTINST CSRs
> are accessed in more optimized manner while running under some other
> hypervisor.
>
> Signed-off-by: Anup Patel <apatel@ventanamicro.com>
> ---
> arch/riscv/kvm/vcpu.c | 34 +++++++++++++++++++++-------------
> 1 file changed, 21 insertions(+), 13 deletions(-)
>
> diff --git a/arch/riscv/kvm/vcpu.c b/arch/riscv/kvm/vcpu.c
> index fe849fb1aaab..854d98aa165e 100644
> --- a/arch/riscv/kvm/vcpu.c
> +++ b/arch/riscv/kvm/vcpu.c
> @@ -757,12 +757,21 @@ static __always_inline void kvm_riscv_vcpu_swap_in_host_state(struct kvm_vcpu *v
> * This must be noinstr as instrumentation may make use of RCU, and this is not
> * safe during the EQS.
> */
> -static void noinstr kvm_riscv_vcpu_enter_exit(struct kvm_vcpu *vcpu)
> +static void noinstr kvm_riscv_vcpu_enter_exit(struct kvm_vcpu *vcpu,
> + struct kvm_cpu_trap *trap)
> {
> void *nsh;
> struct kvm_cpu_context *gcntx = &vcpu->arch.guest_context;
> struct kvm_cpu_context *hcntx = &vcpu->arch.host_context;
>
> + /*
> + * We save trap CSRs (such as SEPC, SCAUSE, STVAL, HTVAL, and
> + * HTINST) here because we do local_irq_enable() after this
> + * function in kvm_arch_vcpu_ioctl_run() which can result in
> + * an interrupt immediately after local_irq_enable() and can
> + * potentially change trap CSRs.
> + */
> +
> kvm_riscv_vcpu_swap_in_guest_state(vcpu);
> guest_state_enter_irqoff();
>
> @@ -805,14 +814,24 @@ static void noinstr kvm_riscv_vcpu_enter_exit(struct kvm_vcpu *vcpu)
> } else {
> gcntx->hstatus = csr_swap(CSR_HSTATUS, hcntx->hstatus);
> }
> +
> + trap->htval = nacl_csr_read(nsh, CSR_HTVAL);
> + trap->htinst = nacl_csr_read(nsh, CSR_HTINST);
> } else {
> hcntx->hstatus = csr_swap(CSR_HSTATUS, gcntx->hstatus);
>
> __kvm_riscv_switch_to(&vcpu->arch);
>
> gcntx->hstatus = csr_swap(CSR_HSTATUS, hcntx->hstatus);
> +
> + trap->htval = csr_read(CSR_HTVAL);
> + trap->htinst = csr_read(CSR_HTINST);
> }
>
> + trap->sepc = gcntx->sepc;
> + trap->scause = csr_read(CSR_SCAUSE);
> + trap->stval = csr_read(CSR_STVAL);
> +
> vcpu->arch.last_exit_cpu = vcpu->cpu;
> guest_state_exit_irqoff();
> kvm_riscv_vcpu_swap_in_host_state(vcpu);
> @@ -929,22 +948,11 @@ int kvm_arch_vcpu_ioctl_run(struct kvm_vcpu *vcpu)
>
> guest_timing_enter_irqoff();
>
> - kvm_riscv_vcpu_enter_exit(vcpu);
> + kvm_riscv_vcpu_enter_exit(vcpu, &trap);
>
> vcpu->mode = OUTSIDE_GUEST_MODE;
> vcpu->stat.exits++;
>
> - /*
> - * Save SCAUSE, STVAL, HTVAL, and HTINST because we might
> - * get an interrupt between __kvm_riscv_switch_to() and
> - * local_irq_enable() which can potentially change CSRs.
> - */
> - trap.sepc = vcpu->arch.guest_context.sepc;
> - trap.scause = csr_read(CSR_SCAUSE);
> - trap.stval = csr_read(CSR_STVAL);
> - trap.htval = ncsr_read(CSR_HTVAL);
> - trap.htinst = ncsr_read(CSR_HTINST);
> -
> /* Syncup interrupts state with HW */
> kvm_riscv_vcpu_sync_interrupts(vcpu);
>
> --
> 2.34.1
>

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