linux-kernel - Re: [PATCH v2 03/10] iommufd: Create access in vfio_iommufd_emulated

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Date:   Thu, 09 Feb 2023 13:58:47 -0500
From:   Eric Farman <farman@...ux.ibm.com>
To:     Nicolin Chen <nicolinc@...dia.com>, jgg@...dia.com,
        kevin.tian@...el.com, joro@...tes.org, will@...nel.org,
        robin.murphy@....com, alex.williamson@...hat.com, shuah@...nel.org
Cc:     yi.l.liu@...el.com, linux-kernel@...r.kernel.org,
        iommu@...ts.linux.dev, kvm@...r.kernel.org,
        linux-kselftest@...r.kernel.org, baolu.lu@...ux.intel.com,
        Matthew Rosato <mjrosato@...ux.ibm.com>
Subject: Re: [PATCH v2 03/10] iommufd: Create access in
 vfio_iommufd_emulated_bind()

On Tue, 2023-02-07 at 13:17 -0800, Nicolin Chen wrote:
...snip...
> diff --git a/drivers/vfio/iommufd.c b/drivers/vfio/iommufd.c
> index 026f81a87dd7..dc9feab73db7 100644
> --- a/drivers/vfio/iommufd.c
> +++ b/drivers/vfio/iommufd.c
> @@ -141,10 +141,19 @@ static const struct iommufd_access_ops
> vfio_user_ops = {
>  int vfio_iommufd_emulated_bind(struct vfio_device *vdev,
>                                struct iommufd_ctx *ictx, u32
> *out_device_id)
>  {
> +       struct iommufd_access *user;
> +
>         lockdep_assert_held(&vdev->dev_set->lock);
>  
> -       vdev->iommufd_ictx = ictx;
>         iommufd_ctx_get(ictx);
> +       user = iommufd_access_create(vdev->iommufd_ictx,
> &vfio_user_ops, vdev);
> +       if (IS_ERR(user)) {
> +               iommufd_ctx_put(vdev->iommufd_ictx);

Matthew noticed a vfio-ccw and -ap regression that blames this patch.

Probably both the iommufd_access_create() and iommufd_ctx_put() calls
want the ictx variable itself, instead of the (uninitialized) pointer
in the vfio_device. (At least that gets -ccw and -ap working again.)

Thanks,
Eric

> +               return PTR_ERR(user);
> +       }
> +       iommufd_access_set_ioas(user, 0);
> +       vdev->iommufd_access = user;
> +       vdev->iommufd_ictx = ictx;
>         return 0;
>  }
>  EXPORT_SYMBOL_GPL(vfio_iommufd_emulated_bind);