linux-kernel - Re: [RFC PATCH v2 24/38] KVM: arm64: Respect virtual HCR

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Date:   Sun, 30 Jul 2017 22:00:25 +0200
From:   Christoffer Dall <cdall@...aro.org>
To:     Jintack Lim <jintack.lim@...aro.org>
Cc:     kvmarm@...ts.cs.columbia.edu, christoffer.dall@...aro.org,
        marc.zyngier@....com, corbet@....net, pbonzini@...hat.com,
        rkrcmar@...hat.com, linux@...linux.org.uk, catalin.marinas@....com,
        will.deacon@....com, akpm@...ux-foundation.org, mchehab@...nel.org,
        cov@...eaurora.org, daniel.lezcano@...aro.org,
        david.daney@...ium.com, mark.rutland@....com,
        suzuki.poulose@....com, stefan@...lo-penguin.com,
        andy.gross@...aro.org, wcohen@...hat.com,
        ard.biesheuvel@...aro.org, shankerd@...eaurora.org,
        vladimir.murzin@....com, james.morse@....com,
        linux-doc@...r.kernel.org, linux-kernel@...r.kernel.org,
        kvm@...r.kernel.org, linux-arm-kernel@...ts.infradead.org
Subject: Re: [RFC PATCH v2 24/38] KVM: arm64: Respect virtual HCR_EL2.TWX
 setting

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@...aro.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
>