linux-kernel - Re: [PATCH v3 6/8] KVM: kvm-vfio: wrapper to VFIO external API device helpers

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Date:	Mon, 24 Nov 2014 13:56:02 -0700
From:	Alex Williamson <alex.williamson@...hat.com>
To:	Eric Auger <eric.auger@...aro.org>
Cc:	eric.auger@...com, christoffer.dall@...aro.org,
	marc.zyngier@....com, linux-arm-kernel@...ts.infradead.org,
	kvmarm@...ts.cs.columbia.edu, kvm@...r.kernel.org,
	joel.schopp@....com, kim.phillips@...escale.com, paulus@...ba.org,
	gleb@...nel.org, pbonzini@...hat.com, agraf@...e.de,
	linux-kernel@...r.kernel.org, patches@...aro.org,
	will.deacon@....com, a.motakis@...tualopensystems.com,
	a.rigo@...tualopensystems.com, john.liuli@...wei.com,
	ming.lei@...onical.com, feng.wu@...el.com
Subject: Re: [PATCH v3 6/8] KVM: kvm-vfio: wrapper to VFIO external API
 device helpers

On Sun, 2014-11-23 at 19:35 +0100, Eric Auger wrote:
> Provide wrapper functions that allow KVM-VFIO device code to
> interact with a vfio device:
> - kvm_vfio_device_get_external_user gets a handle to a struct
>   vfio_device from the vfio device file descriptor and increments
>   its reference counter,
> - kvm_vfio_device_put_external_user decrements the reference counter
>   to a vfio device,
> - kvm_vfio_external_base_device returns a handle to the struct device
>   of the vfio device.
> 
> The KVM-VFIO device uses the VFIO external API device functions.
> 
> Signed-off-by: Eric Auger <eric.auger@...aro.org>
> 
> ---
> 
> v2 -> v3:
> reword the commit message and title
> 
> v1 -> v2:
> - kvm_vfio_external_get_base_device renamed into
>   kvm_vfio_external_base_device
> - kvm_vfio_external_get_type removed
> ---
>  arch/arm/include/asm/kvm_host.h |  5 +++++
>  virt/kvm/vfio.c                 | 45 +++++++++++++++++++++++++++++++++++++++++
>  2 files changed, 50 insertions(+)
> 
> diff --git a/arch/arm/include/asm/kvm_host.h b/arch/arm/include/asm/kvm_host.h
> index 53036e2..bca5b79 100644
> --- a/arch/arm/include/asm/kvm_host.h
> +++ b/arch/arm/include/asm/kvm_host.h
> @@ -169,6 +169,11 @@ void kvm_set_spte_hva(struct kvm *kvm, unsigned long hva, pte_t pte);
>  unsigned long kvm_arm_num_regs(struct kvm_vcpu *vcpu);
>  int kvm_arm_copy_reg_indices(struct kvm_vcpu *vcpu, u64 __user *indices);
>  
> +struct vfio_device;
> +struct vfio_device *kvm_vfio_device_get_external_user(struct file *filep);
> +void kvm_vfio_device_put_external_user(struct vfio_device *vdev);
> +struct device *kvm_vfio_external_base_device(struct vfio_device *vdev);
> +

This doesn't look right, why doesn't kvm-vfio send the struct dev to the
arch callback?  Then the below functions can be static.  Nothing outside
of kvm-vfio device should need to do anything with vfio_device
references.

>  /* We do not have shadow page tables, hence the empty hooks */
>  static inline int kvm_age_hva(struct kvm *kvm, unsigned long start,
>  			      unsigned long end)
> diff --git a/virt/kvm/vfio.c b/virt/kvm/vfio.c
> index 620e37f..6f0cc34 100644
> --- a/virt/kvm/vfio.c
> +++ b/virt/kvm/vfio.c
> @@ -60,6 +60,51 @@ static void kvm_vfio_group_put_external_user(struct vfio_group *vfio_group)
>  	symbol_put(vfio_group_put_external_user);
>  }
>  
> +struct vfio_device *kvm_vfio_device_get_external_user(struct file *filep)
> +{
> +	struct vfio_device *vdev;
> +	struct vfio_device *(*fn)(struct file *);
> +
> +	fn = symbol_get(vfio_device_get_external_user);
> +	if (!fn)
> +		return ERR_PTR(-EINVAL);
> +
> +	vdev = fn(filep);
> +
> +	symbol_put(vfio_device_get_external_user);
> +
> +	return vdev;
> +}
> +
> +void kvm_vfio_device_put_external_user(struct vfio_device *vdev)
> +{
> +	void (*fn)(struct vfio_device *);
> +
> +	fn = symbol_get(vfio_device_put_external_user);
> +	if (!fn)
> +		return;
> +
> +	fn(vdev);
> +
> +	symbol_put(vfio_device_put_external_user);
> +}
> +
> +struct device *kvm_vfio_external_base_device(struct vfio_device *vdev)
> +{
> +	struct device *(*fn)(struct vfio_device *);
> +	struct device *dev;
> +
> +	fn = symbol_get(vfio_external_base_device);
> +	if (!fn)
> +		return NULL;
> +
> +	dev = fn(vdev);
> +
> +	symbol_put(vfio_external_base_device);
> +
> +	return dev;
> +}
> +
>  static bool kvm_vfio_group_is_coherent(struct vfio_group *vfio_group)
>  {
>  	long (*fn)(struct vfio_group *, unsigned long);



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