Re: [PATCH v3 01/10] vfio: Make vfio_unpin_pages() return void

[Anthony Krowiak <akrowiak@linux.ibm.com>]

On 7/8/22 6:44 PM, Nicolin Chen wrote:
> There's only one caller that checks its return value with a WARN_ON_ONCE,
> while all other callers don't check the return value at all. Above that,
> an undo function should not fail. So, simplify the API to return void by
> embedding similar WARN_ONs.
>
> Also for users to pinpoint which condition fails, separate WARN_ON lines,
> yet remove the "driver->ops->unpin_pages" check, since it's unreasonable
> for callers to unpin on something totally random that wasn't even pinned.
> And remove NULL pointer checks for they would trigger oops vs. warnings.
> Note that npage is already validated in the vfio core, thus drop the same
> check in the type1 code.
>
> Suggested-by: Christoph Hellwig <hch@infradead.org>
> Reviewed-by: Christoph Hellwig <hch@lst.de>
> Reviewed-by: Jason Gunthorpe <jgg@nvidia.com>
> Reviewed-by: Kirti Wankhede <kwankhede@nvidia.com>
> Tested-by: Terrence Xu <terrence.xu@intel.com>
> Signed-off-by: Nicolin Chen <nicolinc@nvidia.com>
> ---
>   .../driver-api/vfio-mediated-device.rst       |  2 +-
>   drivers/gpu/drm/i915/gvt/kvmgt.c              |  5 +----
>   drivers/vfio/vfio.c                           | 21 +++++++------------
>   drivers/vfio/vfio.h                           |  2 +-
>   drivers/vfio/vfio_iommu_type1.c               | 15 ++++++-------
>   include/linux/vfio.h                          |  4 ++--
>   6 files changed, 18 insertions(+), 31 deletions(-)
>
> diff --git a/Documentation/driver-api/vfio-mediated-device.rst b/Documentation/driver-api/vfio-mediated-device.rst
> index d7a512676853..4307421dcaa0 100644
> --- a/Documentation/driver-api/vfio-mediated-device.rst
> +++ b/Documentation/driver-api/vfio-mediated-device.rst
> @@ -263,7 +263,7 @@ driver::
>   	int vfio_pin_pages(struct vfio_device *device, unsigned long *user_pfn,
>   				  int npage, int prot, unsigned long *phys_pfn);
>   
> -	int vfio_unpin_pages(struct vfio_device *device, unsigned long *user_pfn,
> +	void vfio_unpin_pages(struct vfio_device *device, unsigned long *user_pfn,
>   				    int npage);
>   
>   These functions call back into the back-end IOMMU module by using the pin_pages
> diff --git a/drivers/gpu/drm/i915/gvt/kvmgt.c b/drivers/gpu/drm/i915/gvt/kvmgt.c
> index e2f6c56ab342..8c67c9aba82d 100644
> --- a/drivers/gpu/drm/i915/gvt/kvmgt.c
> +++ b/drivers/gpu/drm/i915/gvt/kvmgt.c
> @@ -231,18 +231,15 @@ static void intel_gvt_cleanup_vgpu_type_groups(struct intel_gvt *gvt)
>   static void gvt_unpin_guest_page(struct intel_vgpu *vgpu, unsigned long gfn,
>   		unsigned long size)
>   {
> -	struct drm_i915_private *i915 = vgpu->gvt->gt->i915;
>   	int total_pages;
>   	int npage;
> -	int ret;
>   
>   	total_pages = roundup(size, PAGE_SIZE) / PAGE_SIZE;
>   
>   	for (npage = 0; npage < total_pages; npage++) {
>   		unsigned long cur_gfn = gfn + npage;
>   
> -		ret = vfio_unpin_pages(&vgpu->vfio_device, &cur_gfn, 1);
> -		drm_WARN_ON(&i915->drm, ret != 1);
> +		vfio_unpin_pages(&vgpu->vfio_device, &cur_gfn, 1);
>   	}
>   }
>   
> diff --git a/drivers/vfio/vfio.c b/drivers/vfio/vfio.c
> index 100a3d84380c..ad90adbfddc8 100644
> --- a/drivers/vfio/vfio.c
> +++ b/drivers/vfio/vfio.c
> @@ -1964,31 +1964,24 @@ EXPORT_SYMBOL(vfio_pin_pages);
>    *		   PFNs should not be greater than VFIO_PIN_PAGES_MAX_ENTRIES.
>    * @npage [in]   : count of elements in user_pfn array.  This count should not
>    *                 be greater than VFIO_PIN_PAGES_MAX_ENTRIES.
> - * Return error or number of pages unpinned.
>    */
> -int vfio_unpin_pages(struct vfio_device *device, unsigned long *user_pfn,
> -		     int npage)
> +void vfio_unpin_pages(struct vfio_device *device, unsigned long *user_pfn,
> +		      int npage)
>   {
>   	struct vfio_container *container;
>   	struct vfio_iommu_driver *driver;
> -	int ret;
>   
> -	if (!user_pfn || !npage || !vfio_assert_device_open(device))
> -		return -EINVAL;


You left out the check for !user_pfn?


> +	if (WARN_ON(npage <= 0 || npage > VFIO_PIN_PAGES_MAX_ENTRIES))
> +		return;
>   
> -	if (npage > VFIO_PIN_PAGES_MAX_ENTRIES)
> -		return -E2BIG;
> +	if (WARN_ON(!vfio_assert_device_open(device)))
> +		return;
>   
>   	/* group->container cannot change while a vfio device is open */
>   	container = device->group->container;
>   	driver = container->iommu_driver;
> -	if (likely(driver && driver->ops->unpin_pages))
> -		ret = driver->ops->unpin_pages(container->iommu_data, user_pfn,
> -					       npage);
> -	else
> -		ret = -ENOTTY;
>   
> -	return ret;
> +	driver->ops->unpin_pages(container->iommu_data, user_pfn, npage);
>   }
>   EXPORT_SYMBOL(vfio_unpin_pages);
>   
> diff --git a/drivers/vfio/vfio.h b/drivers/vfio/vfio.h
> index a67130221151..bef4edf58138 100644
> --- a/drivers/vfio/vfio.h
> +++ b/drivers/vfio/vfio.h
> @@ -53,7 +53,7 @@ struct vfio_iommu_driver_ops {
>   				     unsigned long *user_pfn,
>   				     int npage, int prot,
>   				     unsigned long *phys_pfn);
> -	int		(*unpin_pages)(void *iommu_data,
> +	void		(*unpin_pages)(void *iommu_data,
>   				       unsigned long *user_pfn, int npage);
>   	int		(*register_notifier)(void *iommu_data,
>   					     unsigned long *events,
> diff --git a/drivers/vfio/vfio_iommu_type1.c b/drivers/vfio/vfio_iommu_type1.c
> index db24062fb343..cfeea4efd625 100644
> --- a/drivers/vfio/vfio_iommu_type1.c
> +++ b/drivers/vfio/vfio_iommu_type1.c
> @@ -948,20 +948,16 @@ static int vfio_iommu_type1_pin_pages(void *iommu_data,
>   	return ret;
>   }
>   
> -static int vfio_iommu_type1_unpin_pages(void *iommu_data,
> -					unsigned long *user_pfn,
> -					int npage)
> +static void vfio_iommu_type1_unpin_pages(void *iommu_data,
> +					 unsigned long *user_pfn, int npage)
>   {
>   	struct vfio_iommu *iommu = iommu_data;
>   	bool do_accounting;
>   	int i;
>   
> -	if (!iommu || !user_pfn || npage <= 0)
> -		return -EINVAL;


Is there a reason the checks above were not checked for WARN_ON?


> -
>   	/* Supported for v2 version only */
> -	if (!iommu->v2)
> -		return -EACCES;
> +	if (WARN_ON(!iommu->v2))
> +		return;
>   
>   	mutex_lock(&iommu->lock);
>   
> @@ -979,7 +975,8 @@ static int vfio_iommu_type1_unpin_pages(void *iommu_data,
>   	}
>   
>   	mutex_unlock(&iommu->lock);
> -	return i > 0 ? i : -EINVAL;
> +
> +	WARN_ON(i != npage);
>   }
>   
>   static long vfio_sync_unpin(struct vfio_dma *dma, struct vfio_domain *domain,
> diff --git a/include/linux/vfio.h b/include/linux/vfio.h
> index 4d26e149db81..5348ef353029 100644
> --- a/include/linux/vfio.h
> +++ b/include/linux/vfio.h
> @@ -159,8 +159,8 @@ bool vfio_file_has_dev(struct file *file, struct vfio_device *device);
>   
>   int vfio_pin_pages(struct vfio_device *device, unsigned long *user_pfn,
>   		   int npage, int prot, unsigned long *phys_pfn);
> -int vfio_unpin_pages(struct vfio_device *device, unsigned long *user_pfn,
> -		     int npage);
> +void vfio_unpin_pages(struct vfio_device *device, unsigned long *user_pfn,
> +		      int npage);
>   int vfio_dma_rw(struct vfio_device *device, dma_addr_t user_iova,
>   		void *data, size_t len, bool write);
>