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

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Date:   Thu, 9 Feb 2023 11:54:07 -0800
From:   Nicolin Chen <nicolinc@...dia.com>
To:     Eric Farman <farman@...ux.ibm.com>
CC:     <jgg@...dia.com>, <kevin.tian@...el.com>, <joro@...tes.org>,
        <will@...nel.org>, <robin.murphy@....com>,
        <alex.williamson@...hat.com>, <shuah@...nel.org>,
        <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 Thu, Feb 09, 2023 at 01:58:47PM -0500, Eric Farman wrote:
> External email: Use caution opening links or attachments
> 
> 
> 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.)

Oops. Yes, it should be:

	iommufd_ctx_get(ictx);
	user = iommufd_access_create(ictx, &vfio_user_ops, vdev);
	if (IS_ERR(user)) {
		iommufd_ctx_put(ictx);

Will fix in v3.

Thanks!
Nic