Re: [RFC 21/55] KVM: arm64: Forward HVC instruction to the guest hypervisor

[Christoffer Dall]

On Mon, Jan 09, 2017 at 01:24:17AM -0500, Jintack Lim wrote:
> Forward exceptions due to hvc instruction to the guest hypervisor.
> 
> Signed-off-by: Jintack Lim <jintack@xxxxxxxxxxxxxxx>
> ---
>  arch/arm64/include/asm/kvm_nested.h |  5 +++++
>  arch/arm64/kvm/Makefile             |  1 +
>  arch/arm64/kvm/handle_exit.c        | 11 +++++++++++
>  arch/arm64/kvm/handle_exit_nested.c | 27 +++++++++++++++++++++++++++
>  4 files changed, 44 insertions(+)
>  create mode 100644 arch/arm64/include/asm/kvm_nested.h
>  create mode 100644 arch/arm64/kvm/handle_exit_nested.c
> 
> diff --git a/arch/arm64/include/asm/kvm_nested.h b/arch/arm64/include/asm/kvm_nested.h
> new file mode 100644
> index 0000000..620b4d3
> --- /dev/null
> +++ b/arch/arm64/include/asm/kvm_nested.h
> @@ -0,0 +1,5 @@
> +#ifndef __ARM64_KVM_NESTED_H__
> +#define __ARM64_KVM_NESTED_H__
> +
> +int handle_hvc_nested(struct kvm_vcpu *vcpu);
> +#endif
> diff --git a/arch/arm64/kvm/Makefile b/arch/arm64/kvm/Makefile
> index b342bdd..9c35e9a 100644
> --- a/arch/arm64/kvm/Makefile
> +++ b/arch/arm64/kvm/Makefile
> @@ -35,4 +35,5 @@ kvm-$(CONFIG_KVM_ARM_HOST) += $(KVM)/irqchip.o
>  kvm-$(CONFIG_KVM_ARM_HOST) += $(KVM)/arm/arch_timer.o
>  kvm-$(CONFIG_KVM_ARM_PMU) += $(KVM)/arm/pmu.o
>  
> +kvm-$(CONFIG_KVM_ARM_NESTED_HYP) += handle_exit_nested.o
>  kvm-$(CONFIG_KVM_ARM_NESTED_HYP) += emulate-nested.o
> diff --git a/arch/arm64/kvm/handle_exit.c b/arch/arm64/kvm/handle_exit.c
> index a891684..208be16 100644
> --- a/arch/arm64/kvm/handle_exit.c
> +++ b/arch/arm64/kvm/handle_exit.c
> @@ -29,6 +29,10 @@
>  #include <asm/kvm_mmu.h>
>  #include <asm/kvm_psci.h>
>  
> +#ifdef CONFIG_KVM_ARM_NESTED_HYP
> +#include <asm/kvm_nested.h>
> +#endif
> +
>  #define CREATE_TRACE_POINTS
>  #include "trace.h"
>  
> @@ -42,6 +46,13 @@ static int handle_hvc(struct kvm_vcpu *vcpu, struct kvm_run *run)
>  			    kvm_vcpu_hvc_get_imm(vcpu));
>  	vcpu->stat.hvc_exit_stat++;
>  
> +#ifdef CONFIG_KVM_ARM_NESTED_HYP
> +	ret = handle_hvc_nested(vcpu);
> +	if (ret < 0 && ret != -EINVAL)
> +		return ret;
> +	else if (ret >= 0)
> +		return ret;
> +#endif
>  	ret = kvm_psci_call(vcpu);
>  	if (ret < 0) {
>  		kvm_inject_undefined(vcpu);
> diff --git a/arch/arm64/kvm/handle_exit_nested.c b/arch/arm64/kvm/handle_exit_nested.c
> new file mode 100644
> index 0000000..a6ce23b
> --- /dev/null
> +++ b/arch/arm64/kvm/handle_exit_nested.c
> @@ -0,0 +1,27 @@
> +/*
> + * Copyright (C) 2016 - Columbia University
> + * Author: Jintack Lim <jintack@xxxxxxxxxxxxxxx>
> + *
> + * This program is free software; you can redistribute it and/or modify
> + * it under the terms of the GNU General Public License version 2 as
> + * published by the Free Software Foundation.
> + *
> + * This program is distributed in the hope that it will be useful,
> + * but WITHOUT ANY WARRANTY; without even the implied warranty of
> + * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
> + * GNU General Public License for more details.
> + *
> + * You should have received a copy of the GNU General Public License
> + * along with this program.  If not, see <http://www.gnu.org/licenses/>.
> + */
> +
> +#include <linux/kvm.h>
> +#include <linux/kvm_host.h>
> +
> +#include <asm/kvm_emulate.h>
> +
> +/* We forward all hvc instruction to the guest hypervisor. */
> +int handle_hvc_nested(struct kvm_vcpu *vcpu)
> +{
> +	return kvm_inject_nested_sync(vcpu, kvm_vcpu_get_hsr(vcpu));
> +}

I don't understand the logic here or in the caller above.  Do we really
forward *all" hvc calls to the guest hypervisor now, so that we no
longer support any hypercalls from the VM?  That seems a little rough
and probably requires some more discussions.

Thanks,
-Christoffer