linux-kernel - Re: [RFC 16/55] KVM: arm64: Forward VM reg traps to the guest hypervisor

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Date:   Wed, 22 Feb 2017 12:39:04 +0100
From:   Christoffer Dall <cdall@...aro.org>
To:     Jintack Lim <jintack@...columbia.edu>
Cc:     christoffer.dall@...aro.org, marc.zyngier@....com,
        pbonzini@...hat.com, rkrcmar@...hat.com, linux@...linux.org.uk,
        catalin.marinas@....com, will.deacon@....com,
        vladimir.murzin@....com, suzuki.poulose@....com,
        mark.rutland@....com, james.morse@....com,
        lorenzo.pieralisi@....com, kevin.brodsky@....com,
        wcohen@...hat.com, shankerd@...eaurora.org, geoff@...radead.org,
        andre.przywara@....com, eric.auger@...hat.com,
        anna-maria@...utronix.de, shihwei@...columbia.edu,
        linux-arm-kernel@...ts.infradead.org, kvmarm@...ts.cs.columbia.edu,
        kvm@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [RFC 16/55] KVM: arm64: Forward VM reg traps to the guest
 hypervisor

On Mon, Jan 09, 2017 at 01:24:12AM -0500, Jintack Lim wrote:
> Forward virtual memory register traps to the guest hypervisor
> if it has set corresponding bits to the virtual HCR_EL2.

I was a bit confused about the subject of this patch.  I would recommend
calling it something like
"Respect virtul HCR_EL2.TVM and HCR_EL2.TRVM settings"

> 
> Signed-off-by: Jintack Lim <jintack@...columbia.edu>
> ---
>  arch/arm64/kvm/sys_regs.c | 20 ++++++++++++++++++++
>  1 file changed, 20 insertions(+)
> 
> diff --git a/arch/arm64/kvm/sys_regs.c b/arch/arm64/kvm/sys_regs.c
> index b8e993a..0f5d21b 100644
> --- a/arch/arm64/kvm/sys_regs.c
> +++ b/arch/arm64/kvm/sys_regs.c
> @@ -90,6 +90,23 @@ static bool access_dcsw(struct kvm_vcpu *vcpu,
>  	return true;
>  }
>  
> +static bool forward_vm_traps(struct kvm_vcpu *vcpu, struct sys_reg_params *p)
> +{
> +	u64 hcr_el2 = vcpu_el2_reg(vcpu, HCR_EL2);
> +
> +	/* If this is a trap from the virtual EL2, the host handles */
> +	if (vcpu_mode_el2(vcpu))
> +		return false;
> +
> +	/* If the guest wants to trap on R/W operation, forward this trap */
> +	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
> @@ -101,6 +118,9 @@ static bool access_vm_reg(struct kvm_vcpu *vcpu,
>  {
>  	bool was_enabled = vcpu_has_cache_enabled(vcpu);
>  
> +	if (forward_vm_traps(vcpu, p))
> +		return kvm_inject_nested_sync(vcpu, kvm_vcpu_get_hsr(vcpu));
> +
>  	BUG_ON(!vcpu_mode_el2(vcpu) && !p->is_write);
>  
>  	if (!p->is_write) {
> -- 
> 1.9.1
> 
>