linux-kernel - Re: [RFC PATCH 1/4] ARM: KVM: on unhandled IO mem abort, route the call to the KVM MMIO bus

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Date:	Fri, 28 Mar 2014 12:09:13 -0700
From:	Christoffer Dall <christoffer.dall@...aro.org>
To:	Antonios Motakis <a.motakis@...tualopensystems.com>
Cc:	kvmarm@...ts.cs.columbia.edu, tech@...tualopensystems.com,
	n.nikolaev@...tualopensystems.com, agraf@...e.de,
	marc.zyngier@....com, Gleb Natapov <gleb@...nel.org>,
	Paolo Bonzini <pbonzini@...hat.com>,
	Russell King <linux@....linux.org.uk>,
	"open list:KERNEL VIRTUAL MA..." <kvm@...r.kernel.org>,
	"moderated list:ARM PORT" <linux-arm-kernel@...ts.infradead.org>,
	open list <linux-kernel@...r.kernel.org>
Subject: Re: [RFC PATCH 1/4] ARM: KVM: on unhandled IO mem abort, route the
 call to the KVM MMIO bus

On Thu, Mar 13, 2014 at 04:57:26PM +0100, Antonios Motakis wrote:
> On an unhandled IO memory abort, use the kvm_io_bus_* API in order to
> handle the MMIO access through any registered read/write callbacks. This
> is a dependency for eventfd support (ioeventfd and irqfd).
> 
> However, accesses to the VGIC are still left implemented independently,
> since the kvm_io_bus_* API doesn't pass the VCPU pointer doing the access.
> 
> Signed-off-by: Antonios Motakis <a.motakis@...tualopensystems.com>
> Signed-off-by: Nikolay Nikolaev <n.nikolaev@...tualopensystems.com>
> ---
>  arch/arm/kvm/mmio.c | 32 ++++++++++++++++++++++++++++++++
>  virt/kvm/arm/vgic.c |  5 ++++-
>  2 files changed, 36 insertions(+), 1 deletion(-)
> 
> diff --git a/arch/arm/kvm/mmio.c b/arch/arm/kvm/mmio.c
> index 4cb5a93..1d17831 100644
> --- a/arch/arm/kvm/mmio.c
> +++ b/arch/arm/kvm/mmio.c
> @@ -162,6 +162,35 @@ static int decode_hsr(struct kvm_vcpu *vcpu, phys_addr_t fault_ipa,
>  	return 0;
>  }
>  
> +/**
> + * kvm_handle_mmio - handle an in-kernel MMIO access
> + * @vcpu:	pointer to the vcpu performing the access
> + * @run:	pointer to the kvm_run structure
> + * @mmio:	pointer to the data describing the access
> + *
> + * returns true if the MMIO access has been performed in kernel space,
> + * and false if it needs to be emulated in user space.
> + */
> +static bool handle_kernel_mmio(struct kvm_vcpu *vcpu, struct kvm_run *run,
> +		struct kvm_exit_mmio *mmio)
> +{
> +	int ret;
> +	if (mmio->is_write) {
> +		ret = kvm_io_bus_write(vcpu->kvm, KVM_MMIO_BUS, mmio->phys_addr,
> +				mmio->len, &mmio->data);
> +
> +	} else {
> +		ret = kvm_io_bus_read(vcpu->kvm, KVM_MMIO_BUS, mmio->phys_addr,
> +				mmio->len, &mmio->data);
> +	}
> +	if (!ret) {
> +		kvm_prepare_mmio(run, mmio);
> +		kvm_handle_mmio_return(vcpu, run);
> +	}
> +
> +	return !ret;
> +}
> +
>  int io_mem_abort(struct kvm_vcpu *vcpu, struct kvm_run *run,
>  		 phys_addr_t fault_ipa)
>  {
> @@ -200,6 +229,9 @@ int io_mem_abort(struct kvm_vcpu *vcpu, struct kvm_run *run,
>  	if (vgic_handle_mmio(vcpu, run, &mmio))
>  		return 1;
>  
> +	if (handle_kernel_mmio(vcpu, run, &mmio))
> +		return 1;
> +

this special-casing of the vgic is now really terrible.  Is there
anything holding you back from doing the necessary restructure of the
kvm_bus_io_*() API instead?  That would allow us to get rid of the ugly
Fix it! in the vgic driver as well.

-Christoffer

>  	kvm_prepare_mmio(run, &mmio);
>  	return 0;
>  }
> diff --git a/virt/kvm/arm/vgic.c b/virt/kvm/arm/vgic.c
> index 8ca405c..afdecc3 100644
> --- a/virt/kvm/arm/vgic.c
> +++ b/virt/kvm/arm/vgic.c
> @@ -849,13 +849,16 @@ struct mmio_range *find_matching_range(const struct mmio_range *ranges,
>  }
>  
>  /**
> - * vgic_handle_mmio - handle an in-kernel MMIO access
> + * vgic_handle_mmio - handle an in-kernel vgic MMIO access
>   * @vcpu:	pointer to the vcpu performing the access
>   * @run:	pointer to the kvm_run structure
>   * @mmio:	pointer to the data describing the access
>   *
>   * returns true if the MMIO access has been performed in kernel space,
>   * and false if it needs to be emulated in user space.
> + *
> + * This is handled outside of kvm_handle_mmio because the kvm_io_bus only
> + * passes the VM pointer, while we need the VCPU performing the access.
>   */
>  bool vgic_handle_mmio(struct kvm_vcpu *vcpu, struct kvm_run *run,
>  		      struct kvm_exit_mmio *mmio)
> -- 
> 1.8.3.2
> 
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