linux-kernel - Re: [PATCH v6 07/25] iommufd/access: Add internal APIs for HW queue to use

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Message-ID: <aFDSNYOTToFSbFA2@nvidia.com>
Date: Mon, 16 Jun 2025 19:25:57 -0700
From: Nicolin Chen <nicolinc@...dia.com>
To: Jason Gunthorpe <jgg@...dia.com>
CC: <kevin.tian@...el.com>, <corbet@....net>, <will@...nel.org>,
	<bagasdotme@...il.com>, <robin.murphy@....com>, <joro@...tes.org>,
	<thierry.reding@...il.com>, <vdumpa@...dia.com>, <jonathanh@...dia.com>,
	<shuah@...nel.org>, <jsnitsel@...hat.com>, <nathan@...nel.org>,
	<peterz@...radead.org>, <yi.l.liu@...el.com>, <mshavit@...gle.com>,
	<praan@...gle.com>, <zhangzekun11@...wei.com>, <iommu@...ts.linux.dev>,
	<linux-doc@...r.kernel.org>, <linux-kernel@...r.kernel.org>,
	<linux-arm-kernel@...ts.infradead.org>, <linux-tegra@...r.kernel.org>,
	<linux-kselftest@...r.kernel.org>, <patches@...ts.linux.dev>,
	<mochs@...dia.com>, <alok.a.tiwari@...cle.com>, <vasant.hegde@....com>,
	<dwmw2@...radead.org>, <baolu.lu@...ux.intel.com>
Subject: Re: [PATCH v6 07/25] iommufd/access: Add internal APIs for HW queue
 to use

On Mon, Jun 16, 2025 at 10:37:19AM -0300, Jason Gunthorpe wrote:
> On Sat, Jun 14, 2025 at 12:14:32AM -0700, Nicolin Chen wrote:
> > Now, access->ops can be NULL, to support an internal use case for the new
> > HW queue object. Since an access object in this case will be allocated by
> > an inernal iommufd object, the refcount on the ictx should be skipped, so
> > as not to deadlock the release of the ictx as it would otherwise wait for
> > the release of the access first during the release of the internal object
> > that could wait for the release of ictx:
> >     ictx --releases--> hw_queue --releases--> access
> >       ^                                         |
> >       |_________________releases________________v
> > 
> > Add a set of lightweight internal APIs to unlink access and ictx:
> >     ictx --releases--> hw_queue --releases--> access
> > 
> > Signed-off-by: Nicolin Chen <nicolinc@...dia.com>
> > ---
> >  drivers/iommu/iommufd/iommufd_private.h |  8 ++++
> >  drivers/iommu/iommufd/device.c          | 59 +++++++++++++++++++++----
> >  2 files changed, 58 insertions(+), 9 deletions(-)
> > 
> > diff --git a/drivers/iommu/iommufd/iommufd_private.h b/drivers/iommu/iommufd/iommufd_private.h
> > index 4a375a8c9216..468717d5e5bc 100644
> > --- a/drivers/iommu/iommufd/iommufd_private.h
> > +++ b/drivers/iommu/iommufd/iommufd_private.h
> > @@ -484,6 +484,14 @@ void iopt_remove_access(struct io_pagetable *iopt,
> >  			struct iommufd_access *access, u32 iopt_access_list_id);
> >  void iommufd_access_destroy_object(struct iommufd_object *obj);
> >  
> > +/* iommufd_access for internal use */
> > +struct iommufd_access *iommufd_access_create_internal(struct iommufd_ctx *ictx);
> > +#define iommufd_access_destroy_internal(ictx, access) \
> > +	iommufd_object_destroy_user(ictx, &(access)->obj)
> 
> Use a static inline please
> 
> > +int iommufd_access_attach_internal(struct iommufd_access *access,
> > +				   struct iommufd_ioas *ioas);
> > +#define iommufd_access_detach_internal(access) iommufd_access_detach(access)
> 
> 
> >  struct iommufd_eventq {
> >  	struct iommufd_object obj;
> >  	struct iommufd_ctx *ictx;
> > diff --git a/drivers/iommu/iommufd/device.c b/drivers/iommu/iommufd/device.c
> > index 9293722b9cff..ad33f1e41a24 100644
> > --- a/drivers/iommu/iommufd/device.c
> > +++ b/drivers/iommu/iommufd/device.c
> > @@ -1084,7 +1084,39 @@ void iommufd_access_destroy_object(struct iommufd_object *obj)
> >  	if (access->ioas)
> >  		WARN_ON(iommufd_access_change_ioas(access, NULL));
> >  	mutex_unlock(&access->ioas_lock);
> > -	iommufd_ctx_put(access->ictx);
> > +	if (access->ops)
> > +		iommufd_ctx_put(access->ictx);
> 
> I was hoping we could null the ictx to signal internal? That didn't
> work out?

access->ictx should be NULL for internal. It should have been:
+	if (access->ictx)
+		iommufd_ctx_put(access->ictx);

> I would at least add a comment here this is filtering internal that
> doesn't have ictx. Maybe a little inline 'iommufd_access_is_internal'
> is appropriate. We'll be sad down the road if we need ops for
> internal.

Yea, an inline will be cleaner. Will add that.

Thanks
Nicolin