linux-kernel - Re: [RFC PATCH v2 35/38] KVM: arm64: Respect the virtual HCR_EL2.NV bit setting for EL12 register traps

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Date:   Mon, 31 Jul 2017 14:39:01 +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 35/38] KVM: arm64: Respect the virtual HCR_EL2.NV
 bit setting for EL12 register traps

On Tue, Jul 18, 2017 at 11:59:01AM -0500, Jintack Lim wrote:
> In addition to EL2 register accesses, setting NV bit will also make EL12
> register accesses trap to EL2. To emulate this for the virtual EL2,
> forword traps due to EL12 register accessses to the virtual EL2 if the
> virtual HCR_EL2.NV bit is set.
> 
> This is for recursive nested virtualization.

> 
> Signed-off-by: Jintack Lim <jintack.lim@...aro.org>
> ---
>  arch/arm64/kvm/sys_regs.c | 18 ++++++++++++++++++
>  1 file changed, 18 insertions(+)
> 
> diff --git a/arch/arm64/kvm/sys_regs.c b/arch/arm64/kvm/sys_regs.c
> index 4fd7090..3559cf7 100644
> --- a/arch/arm64/kvm/sys_regs.c
> +++ b/arch/arm64/kvm/sys_regs.c
> @@ -149,6 +149,9 @@ static bool access_vm_reg(struct kvm_vcpu *vcpu,
>  	int i;
>  	const struct el1_el2_map *map;
>  
> +	if (el12_reg(p) && forward_nv_traps(vcpu))
> +		return kvm_inject_nested_sync(vcpu, kvm_vcpu_get_hsr(vcpu));
> +
>  	/*
>  	 * Redirect EL1 register accesses to the corresponding EL2 registers if
>  	 * they are meant to access EL2 registers.
> @@ -959,6 +962,9 @@ static bool access_cntkctl_el12(struct kvm_vcpu *vcpu,
>  			 struct sys_reg_params *p,
>  			 const struct sys_reg_desc *r)
>  {
> +	if (forward_nv_traps(vcpu))
> +		return kvm_inject_nested_sync(vcpu, kvm_vcpu_get_hsr(vcpu));
> +
>  	access_rw(p, &vcpu_sys_reg(vcpu, r->reg));
>  	return true;
>  }
> @@ -1005,6 +1011,9 @@ static bool access_elr(struct kvm_vcpu *vcpu,
>  		struct sys_reg_params *p,
>  		const struct sys_reg_desc *r)
>  {
> +	if (el12_reg(p) && forward_nv_traps(vcpu))
> +		return kvm_inject_nested_sync(vcpu, kvm_vcpu_get_hsr(vcpu));
> +
>  	access_rw(p, &vcpu->arch.ctxt.gp_regs.elr_el1);
>  	return true;
>  }
> @@ -1013,6 +1022,9 @@ static bool access_spsr(struct kvm_vcpu *vcpu,
>  		struct sys_reg_params *p,
>  		const struct sys_reg_desc *r)
>  {
> +	if (el12_reg(p) && forward_nv_traps(vcpu))
> +		return kvm_inject_nested_sync(vcpu, kvm_vcpu_get_hsr(vcpu));
> +
>  	access_rw(p, &vcpu->arch.ctxt.gp_regs.spsr[KVM_SPSR_EL1]);
>  	return true;
>  }
> @@ -1021,6 +1033,9 @@ static bool access_vbar(struct kvm_vcpu *vcpu,
>  		struct sys_reg_params *p,
>  		const struct sys_reg_desc *r)
>  {
> +	if (el12_reg(p) && forward_nv_traps(vcpu))
> +		return kvm_inject_nested_sync(vcpu, kvm_vcpu_get_hsr(vcpu));
> +
>  	access_rw(p, &vcpu_sys_reg(vcpu, r->reg));
>  	return true;
>  }
> @@ -1031,6 +1046,9 @@ static bool access_cpacr(struct kvm_vcpu *vcpu,
>  {
>  	u64 reg = sys_reg(p->Op0, p->Op1, p->CRn, p->CRm, p->Op2);
>  
> +	if (el12_reg(p) && forward_nv_traps(vcpu))
> +		return kvm_inject_nested_sync(vcpu, kvm_vcpu_get_hsr(vcpu));
> +
>  	/*
>  	 * When the virtual HCR_EL2.E2H == 1, an access to CPACR_EL1
>  	 * in the virtual EL2 is to access CPTR_EL2.
> -- 
> 1.9.1
> 

I'm wondering instead of having all these handlers, could we add this at
a higher level, like kvm_handle_sys() instead?

Thanks,
-Christoffer