Re: [RFC PATCH v2 24/38] KVM: arm64: Respect virtual HCR_EL2.TWX setting

Christoffer Dall
2017-07-30T20:00:35Z

On Tue, Jul 18, 2017 at 11:58:50AM -0500, Jintack Lim wrote:
> Forward exceptions due to WFI or WFE instructions to the virtual EL2 if
> they are not coming from the virtual EL2 and virtual HCR_EL2.TWX is set.
>
> Signed-off-by: Jintack Lim <jintack.lim@linaro.org>
> ---
> arch/arm64/include/asm/kvm_host.h | 1 +
> arch/arm64/kvm/handle_exit.c | 13 ++++++++++++-
> arch/arm64/kvm/nested.c | 20 ++++++++++++++++++++
> 3 files changed, 33 insertions(+), 1 deletion(-)
>
> diff --git a/arch/arm64/include/asm/kvm_host.h b/arch/arm64/include/asm/kvm_host.h
> index 46880c3..53b0b33 100644
> --- a/arch/arm64/include/asm/kvm_host.h
> +++ b/arch/arm64/include/asm/kvm_host.h
> @@ -442,5 +442,6 @@ static inline void __cpu_init_stage2(void)
> int __init kvmarm_nested_cfg(char *buf);
> int init_nested_virt(void);
> bool nested_virt_in_use(struct kvm_vcpu *vcpu);
> +int handle_wfx_nested(struct kvm_vcpu *vcpu, bool is_wfe);
>
> #endif /* __ARM64_KVM_HOST_H__ */
> diff --git a/arch/arm64/kvm/handle_exit.c b/arch/arm64/kvm/handle_exit.c
> index 8b398b2..25ec824 100644
> --- a/arch/arm64/kvm/handle_exit.c
> +++ b/arch/arm64/kvm/handle_exit.c
> @@ -107,7 +107,18 @@ static int handle_no_fpsimd(struct kvm_vcpu *vcpu, struct kvm_run *run)
> */
> static int kvm_handle_wfx(struct kvm_vcpu *vcpu, struct kvm_run *run)
> {
> - if (kvm_vcpu_get_hsr(vcpu) & ESR_ELx_WFx_ISS_WFE) {
> + bool is_wfe = !!(kvm_vcpu_get_hsr(vcpu) & ESR_ELx_WFx_ISS_WFE);
> +
> + if (nested_virt_in_use(vcpu)) {
> + int ret = handle_wfx_nested(vcpu, is_wfe);
> +
> + if (ret < 0 && ret != -EINVAL)
> + return ret;
> + else if (ret >= 0)
> + return ret;

This is very complicated and you're not documenting the return value of
handle_wfx_nested.

If you get rid of the defensive statement in kvm_inject_nested, you can
turn that one into a void, and handle_wfx_nested can become a bool, and
then this becomes:

if (ret)
return 1;

If for some reason you don't like that, you can still just do:

if (ret == 1)
return 1;

> + }
> +
> + if (is_wfe) {
> trace_kvm_wfx_arm64(*vcpu_pc(vcpu), true);
> vcpu->stat.wfe_exit_stat++;
> kvm_vcpu_on_spin(vcpu);
> diff --git a/arch/arm64/kvm/nested.c b/arch/arm64/kvm/nested.c
> index 9a05c76..042d304 100644
> --- a/arch/arm64/kvm/nested.c
> +++ b/arch/arm64/kvm/nested.c
> @@ -18,6 +18,8 @@
> #include <linux/kvm.h>
> #include <linux/kvm_host.h>
>
> +#include <asm/kvm_emulate.h>
> +
> static bool nested_param;
>
> int __init kvmarm_nested_cfg(char *buf)
> @@ -41,3 +43,21 @@ bool nested_virt_in_use(struct kvm_vcpu *vcpu)
>
> return false;
> }
> +
> +/*
> + * Inject wfx to the virtual EL2 if this is not from the virtual EL2 and
> + * the virtual HCR_EL2.TWX is set. Otherwise, let the host hypervisor
> + * handle this.
> + */
> +int handle_wfx_nested(struct kvm_vcpu *vcpu, bool is_wfe)
> +{
> + u64 hcr_el2 = vcpu_sys_reg(vcpu, HCR_EL2);
> +
> + if (vcpu_mode_el2(vcpu))
> + return -EINVAL;
> +
> + if ((is_wfe && (hcr_el2 & HCR_TWE)) || (!is_wfe && (hcr_el2 & HCR_TWI)))
> + return kvm_inject_nested_sync(vcpu, kvm_vcpu_get_hsr(vcpu));
> +
> + return -EINVAL;
> +}
> --
> 1.9.1
>