All of lore.kernel.org
 help / color / mirror / Atom feed
From: Joerg Roedel <jroedel@suse.de>
To: Robin Murphy <robin.murphy@arm.com>
Cc: iommu@lists.linux-foundation.org, Tom Murphy <murphyt7@tcd.ie>,
	linux-kernel@vger.kernel.org
Subject: Re: [PATCH] iommu: Implement deferred domain attachment
Date: Fri, 15 May 2020 20:26:00 +0200	[thread overview]
Message-ID: <20200515182600.GJ8135@suse.de> (raw)
In-Reply-To: <e7bdcbf1-a713-618d-3e02-037f509a17e9@arm.com>

On Fri, May 15, 2020 at 05:28:53PM +0100, Robin Murphy wrote:
> On 2020-05-15 17:14, Joerg Roedel wrote:
> > diff --git a/drivers/iommu/dma-iommu.c b/drivers/iommu/dma-iommu.c
> > index ba128d1cdaee..403fda04ea98 100644
> > --- a/drivers/iommu/dma-iommu.c
> > +++ b/drivers/iommu/dma-iommu.c
> > @@ -362,8 +362,8 @@ static int iommu_dma_deferred_attach(struct device *dev,
> >   		return 0;
> >   	if (unlikely(ops->is_attach_deferred &&
> > -			ops->is_attach_deferred(domain, dev)))
> > -		return iommu_attach_device(domain, dev);
> > +		     ops->is_attach_deferred(domain, dev)))
> > +		return iommu_attach_device_no_defer(domain, dev);
> 
> Wouldn't it be simpler to just invoke ops->attach_dev directly and avoid
> having to formalise a public interface that nobody else should ever use
> anyway?

That would omit the ops->attach_dev != NULL check and the trace-point on
device attach. Besides that, it would be a layering violation. But the
function is of course entirely internal to the iommu subsytem and is a
good canditate to be moved to a header file in drivers/iommu.

> @@ -746,8 +747,11 @@ int iommu_group_add_device(struct iommu_group *group,
> struct device *dev)
> 
>         mutex_lock(&group->mutex);
>         list_add_tail(&device->list, &group->devices);
> -       if (group->domain)
> -               ret = __iommu_attach_device(group->domain, dev);
> +       domain = group->domain;
> +       if (domain && (!domain->ops->is_attach_deferred ||
> +                      !domain->ops->is_attach_deferred(domain, dev)))
> +               ret = __iommu_attach_device(domain, dev);
> +       }
>         mutex_unlock(&group->mutex);
>         if (ret)
>                 goto err_put_group;

No, doing this in iommu_group_add_device() doesn't solve the problem.
The attach must not happen before a device driver took control of the
device and silenced any DMA initiated by the old kernel. At probe time
this isn't guaranteed.


	Joerg

_______________________________________________
iommu mailing list
iommu@lists.linux-foundation.org
https://lists.linuxfoundation.org/mailman/listinfo/iommu

WARNING: multiple messages have this Message-ID (diff)
From: Joerg Roedel <jroedel@suse.de>
To: Robin Murphy <robin.murphy@arm.com>
Cc: Joerg Roedel <joro@8bytes.org>,
	iommu@lists.linux-foundation.org, linux-kernel@vger.kernel.org,
	Tom Murphy <murphyt7@tcd.ie>,
	jsnitsel@redhat.com
Subject: Re: [PATCH] iommu: Implement deferred domain attachment
Date: Fri, 15 May 2020 20:26:00 +0200	[thread overview]
Message-ID: <20200515182600.GJ8135@suse.de> (raw)
In-Reply-To: <e7bdcbf1-a713-618d-3e02-037f509a17e9@arm.com>

On Fri, May 15, 2020 at 05:28:53PM +0100, Robin Murphy wrote:
> On 2020-05-15 17:14, Joerg Roedel wrote:
> > diff --git a/drivers/iommu/dma-iommu.c b/drivers/iommu/dma-iommu.c
> > index ba128d1cdaee..403fda04ea98 100644
> > --- a/drivers/iommu/dma-iommu.c
> > +++ b/drivers/iommu/dma-iommu.c
> > @@ -362,8 +362,8 @@ static int iommu_dma_deferred_attach(struct device *dev,
> >   		return 0;
> >   	if (unlikely(ops->is_attach_deferred &&
> > -			ops->is_attach_deferred(domain, dev)))
> > -		return iommu_attach_device(domain, dev);
> > +		     ops->is_attach_deferred(domain, dev)))
> > +		return iommu_attach_device_no_defer(domain, dev);
> 
> Wouldn't it be simpler to just invoke ops->attach_dev directly and avoid
> having to formalise a public interface that nobody else should ever use
> anyway?

That would omit the ops->attach_dev != NULL check and the trace-point on
device attach. Besides that, it would be a layering violation. But the
function is of course entirely internal to the iommu subsytem and is a
good canditate to be moved to a header file in drivers/iommu.

> @@ -746,8 +747,11 @@ int iommu_group_add_device(struct iommu_group *group,
> struct device *dev)
> 
>         mutex_lock(&group->mutex);
>         list_add_tail(&device->list, &group->devices);
> -       if (group->domain)
> -               ret = __iommu_attach_device(group->domain, dev);
> +       domain = group->domain;
> +       if (domain && (!domain->ops->is_attach_deferred ||
> +                      !domain->ops->is_attach_deferred(domain, dev)))
> +               ret = __iommu_attach_device(domain, dev);
> +       }
>         mutex_unlock(&group->mutex);
>         if (ret)
>                 goto err_put_group;

No, doing this in iommu_group_add_device() doesn't solve the problem.
The attach must not happen before a device driver took control of the
device and silenced any DMA initiated by the old kernel. At probe time
this isn't guaranteed.


	Joerg


  reply	other threads:[~2020-05-15 18:26 UTC|newest]

Thread overview: 22+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2020-05-15  9:45 [PATCH] iommu: Implement deferred domain attachment Joerg Roedel
2020-05-15  9:45 ` Joerg Roedel
2020-05-15 13:51 ` Lu Baolu
2020-05-15 13:51   ` Lu Baolu
2020-05-15 14:20   ` Joerg Roedel
2020-05-15 14:20     ` Joerg Roedel
2020-05-15 15:42 ` Robin Murphy
2020-05-15 15:42   ` Robin Murphy
2020-05-15 16:14   ` Joerg Roedel
2020-05-15 16:14     ` Joerg Roedel
2020-05-15 16:28     ` Robin Murphy
2020-05-15 16:28       ` Robin Murphy
2020-05-15 18:26       ` Joerg Roedel [this message]
2020-05-15 18:26         ` Joerg Roedel
2020-05-15 19:23         ` Robin Murphy
2020-05-15 19:23           ` Robin Murphy
2020-05-18 13:26           ` Joerg Roedel
2020-05-18 13:26             ` Joerg Roedel
2020-05-18 22:15             ` Jerry Snitselaar
2020-05-18 22:15               ` Jerry Snitselaar
2020-05-19  7:09             ` Jerry Snitselaar
2020-05-19  7:09               ` Jerry Snitselaar

Reply instructions:

You may reply publicly to this message via plain-text email
using any one of the following methods:

* Save the following mbox file, import it into your mail client,
  and reply-to-all from there: mbox

  Avoid top-posting and favor interleaved quoting:
  https://en.wikipedia.org/wiki/Posting_style#Interleaved_style

* Reply using the --to, --cc, and --in-reply-to
  switches of git-send-email(1):

  git send-email \
    --in-reply-to=20200515182600.GJ8135@suse.de \
    --to=jroedel@suse.de \
    --cc=iommu@lists.linux-foundation.org \
    --cc=linux-kernel@vger.kernel.org \
    --cc=murphyt7@tcd.ie \
    --cc=robin.murphy@arm.com \
    /path/to/YOUR_REPLY

  https://kernel.org/pub/software/scm/git/docs/git-send-email.html

* If your mail client supports setting the In-Reply-To header
  via mailto: links, try the mailto: link
Be sure your reply has a Subject: header at the top and a blank line before the message body. 
This is an external index of several public inboxes,
see mirroring instructions on how to clone and mirror
all data and code used by this external index.