linux-kernel - Re: [RFC PATCH v2 36/38] KVM: arm64: Respect virtual HCR

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Date:   Mon, 31 Jul 2017 14:42:07 +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 36/38] KVM: arm64: Respect virtual HCR_EL2.TVM and
 TRVM settings

On Tue, Jul 18, 2017 at 11:59:02AM -0500, Jintack Lim wrote:
> Forward the EL1 virtual memory register traps to the virtual EL2 if they
> are not coming from the virtual EL2 and the virtual HCR_EL2.TVM or TRVM
> bit is set.

I noticed that all these recursive patches don't change how we program
the physical HCR_EL2.  Is that because we always respect the guest
hypervisor's configuration of the virtual HCR_EL2 into the physical one
when running the VM?

If so, perhaps we should add a single sentence in the commit messages
about that.

> 
> This is for recursive nested virtualization.
> 
> Signed-off-by: Jintack Lim <jintack.lim@...aro.org>
> ---
>  arch/arm64/kvm/sys_regs.c | 24 ++++++++++++++++++++++++
>  1 file changed, 24 insertions(+)
> 
> diff --git a/arch/arm64/kvm/sys_regs.c b/arch/arm64/kvm/sys_regs.c
> index 3559cf7..3e4ec5e 100644
> --- a/arch/arm64/kvm/sys_regs.c
> +++ b/arch/arm64/kvm/sys_regs.c
> @@ -135,6 +135,27 @@ static inline bool el12_reg(struct sys_reg_params *p)
>  	return (p->Op1 == 5);
>  }
>  
> +/* This function is to support the recursive nested virtualization */

it's just 'recursive nested virtualization', not 'the recursive nested
virtualization', and I also think 'recursive virtualization' is
sufficient.

> +static bool forward_vm_traps(struct kvm_vcpu *vcpu, struct sys_reg_params *p)
> +{
> +	u64 hcr_el2 = vcpu_sys_reg(vcpu, HCR_EL2);
> +
> +	/* If a trap comes from the virtual EL2, the host hypervisor handles. */
> +	if (vcpu_mode_el2(vcpu))
> +		return false;
> +
> +	/*
> +	 * If the virtual HCR_EL2.TVM or TRVM bit is set, we need to foward
> +	 * this trap to the virtual EL2.
> +	 */
> +	if ((hcr_el2 & HCR_TVM) && p->is_write)
> +		return true;
> +	else if ((hcr_el2 & HCR_TRVM) && !p->is_write)
> +		return true;
> +
> +	return false;
> +}
> +
>  /*
>   * Generic accessor for VM registers. Only called as long as HCR_TVM
>   * is set. If the guest enables the MMU, we stop trapping the VM
> @@ -152,6 +173,9 @@ static bool access_vm_reg(struct kvm_vcpu *vcpu,
>  	if (el12_reg(p) && forward_nv_traps(vcpu))
>  		return kvm_inject_nested_sync(vcpu, kvm_vcpu_get_hsr(vcpu));
>  
> +	if (!el12_reg(p) && forward_vm_traps(vcpu, p))
> +		return kvm_inject_nested_sync(vcpu, kvm_vcpu_get_hsr(vcpu));

why do you need the !el12_reg(p) check here?

> +
>  	/*
>  	 * Redirect EL1 register accesses to the corresponding EL2 registers if
>  	 * they are meant to access EL2 registers.
> -- 
> 1.9.1
> 

Thanks,
-Christoffer