linux-kernel - Re: [PATCH v3 03/11] iommufd: Introduce IOMMUFD_OBJ

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Message-ID: <CABQgh9GAyGNPz1KNCm3ZT9dtECdGyKU-L_aNnahY8K=RG7AODg@mail.gmail.com>
Date: Wed, 16 Oct 2024 15:08:49 +0800
From: Zhangfei Gao <zhangfei.gao@...aro.org>
To: Nicolin Chen <nicolinc@...dia.com>
Cc: jgg@...dia.com, kevin.tian@...el.com, will@...nel.org, joro@...tes.org, 
	suravee.suthikulpanit@....com, robin.murphy@....com, dwmw2@...radead.org, 
	baolu.lu@...ux.intel.com, shuah@...nel.org, linux-kernel@...r.kernel.org, 
	iommu@...ts.linux.dev, linux-arm-kernel@...ts.infradead.org, 
	linux-kselftest@...r.kernel.org, eric.auger@...hat.com, 
	jean-philippe@...aro.org, mdf@...nel.org, mshavit@...gle.com, 
	shameerali.kolothum.thodi@...wei.com, smostafa@...gle.com, yi.l.liu@...el.com, 
	aik@....com, patches@...ts.linux.dev
Subject: Re: [PATCH v3 03/11] iommufd: Introduce IOMMUFD_OBJ_VIOMMU and its
 related struct

On Wed, 16 Oct 2024 at 14:52, Nicolin Chen <nicolinc@...dia.com> wrote:
>
> On Wed, Oct 16, 2024 at 09:56:51AM +0800, Zhangfei Gao wrote:
> > On Wed, 16 Oct 2024 at 02:44, Nicolin Chen <nicolinc@...dia.com> wrote:
> > >
> > > On Mon, Oct 14, 2024 at 07:01:40PM -0700, Nicolin Chen wrote:
> > > > On Tue, Oct 15, 2024 at 09:15:01AM +0800, Zhangfei Gao wrote:
> > > >
> > > > > > > iommufd_device_bind
> > > > > > > iommufd_device_attach
> > > > > > > iommufd_vdevice_alloc_ioctl
> > > > > > >
> > > > > > > iommufd_device_detach
> > > > > > > iommufd_device_unbind // refcount check fail
> > > > > > > iommufd_vdevice_destroy ref--
> > > > > >
> > > > > > Things should be symmetric. As you suspected, vdevice should be
> > > > > > destroyed before iommufd_device_detach.
> > > > >
> > > > > I am trying based on your for_iommufd_viommu_p2-v3 branch, do you have
> > > > > this issue?
> > > > > In checking whether close fd before unbind?
> > > >
> > > > Oops, my bad. I will provide a fix.
> > >
> > > This should fix the problem:
> > >
> > > ---------------------------------------------------------------------
> > > diff --git a/drivers/iommu/iommufd/device.c b/drivers/iommu/iommufd/device.c
> > > index 5fd3dd420290..13100cfea29d 100644
> > > --- a/drivers/iommu/iommufd/device.c
> > > +++ b/drivers/iommu/iommufd/device.c
> > > @@ -277,6 +277,11 @@ EXPORT_SYMBOL_NS_GPL(iommufd_ctx_has_group, IOMMUFD);
> > >   */
> > >  void iommufd_device_unbind(struct iommufd_device *idev)
> > >  {
> > > +       mutex_lock(&idev->igroup->lock);
> > > +       /* idev->vdev object should be destroyed prior, yet just in case.. */
> > > +       if (idev->vdev)
> > > +               iommufd_object_remove(idev->ictx, NULL, idev->vdev->obj.id, 0);
> > > +       mutex_unlock(&idev->igroup->lock);
> > >         iommufd_object_destroy_user(idev->ictx, &idev->obj);
> > >  }
> > >  EXPORT_SYMBOL_NS_GPL(iommufd_device_unbind, IOMMUFD);
> > > ---------------------------------------------------------------------
> >
> > Not yet
> > [  574.162112] Unable to handle kernel NULL pointer dereference at
> > virtual address 0000000000000004
> > [  574.261102] pc : iommufd_object_remove+0x7c/0x278
> > [  574.265795] lr : iommufd_device_unbind+0x44/0x98
> > in check
>
> Hmm, it's kinda odd it crashes inside iommufd_object_remove().
> Did you happen to change something there?
>
> The added iommufd_object_remove() is equivalent to userspace
> calling the destroy ioctl on the vDEVICE object.
>
Yes, double confirmed, it can solve the issue.
The guest can stop and run again

The Null pointer may be caused by the added debug.

Thanks Nico.

> Nicolin