Re: [PATCH 01/11] iommu: Add device dma ownership set/release interfaces

[Lu Baolu]

Hi Jason,

On 11/16/21 9:46 PM, Jason Gunthorpe wrote:
> On Tue, Nov 16, 2021 at 09:57:30AM +0800, Lu Baolu wrote:
> > Hi Christoph,
> >
> > On 11/15/21 9:14 PM, Christoph Hellwig wrote:
> > > On Mon, Nov 15, 2021 at 10:05:42AM +0800, Lu Baolu wrote:
> > > > +enum iommu_dma_owner {
> > > > +	DMA_OWNER_NONE,
> > > > +	DMA_OWNER_KERNEL,
> > > > +	DMA_OWNER_USER,
> > > > +};
> > > > +
> > >
> > > > +	enum iommu_dma_owner dma_owner;
> > > > +	refcount_t owner_cnt;
> > > > +	struct file *owner_user_file;
> > >
> > > I'd just overload the ownership into owner_user_file,
> > >
> > >    NULL			-> no owner
> > >    (struct file *)1UL)	-> kernel
> > >    real pointer		-> user
> > >
> > > Which could simplify a lot of the code dealing with the owner.
> >
> > Yeah! Sounds reasonable. I will make this in the next version.
>
> It would be good to figure out how to make iommu_attach_device()
> enforce no other driver binding as a kernel user without a file *, as
> Robin pointed to, before optimizing this.
>
> This fixes an existing bug where iommu_attach_device() only checks the
> group size and is vunerable to a hot plug increasing the group size
> after it returns. That check should be replaced by this series's logic
> instead.

As my my understanding, the essence of this problem is that only the
user owner of the iommu_group could attach an UNMANAGED domain to it.
If I understand it right, how about introducing a new interface to
allocate a user managed domain and storing the user file pointer in it.

--- a/include/linux/iommu.h
+++ b/include/linux/iommu.h
@@ -94,6 +94,7 @@ struct iommu_domain {
        void *handler_token;
        struct iommu_domain_geometry geometry;
        struct iommu_dma_cookie *iova_cookie;
+       struct file *owner_user_file;
 };
--- a/drivers/iommu/iommu.c
+++ b/drivers/iommu/iommu.c
@@ -1902,6 +1902,18 @@ struct iommu_domain *iommu_domain_alloc(struct 
bus_type *bus)
 }
 EXPORT_SYMBOL_GPL(iommu_domain_alloc);

+struct iommu_domain *iommu_domain_alloc_user(struct bus_type *bus,
+                                            struct file *filep)
+{
+       struct iommu_domain *domain;
+
+       domain = __iommu_domain_alloc(bus, IOMMU_DOMAIN_UNMANAGED);
+       if (domain)
+               domain->owner_user_file = filep;
+
+       return domain;
+}

When attaching a domain to an user-owned iommu_group, both group and
domain should have matched user fd.

Does above help here?

Best regards,
baolu