Re: [PATCH kernel v9 26/32] powerpc/iommu: Add userspace view of TCE table

[Alexey Kardashevskiy]

On 05/05/2015 10:02 PM, David Gibson wrote:
> On Fri, May 01, 2015 at 05:12:45PM +1000, Alexey Kardashevskiy wrote:
> > On 05/01/2015 02:23 PM, David Gibson wrote:
> > > On Fri, May 01, 2015 at 02:01:17PM +1000, Alexey Kardashevskiy wrote:
> > > > On 04/29/2015 04:31 PM, David Gibson wrote:
> > > > > On Sat, Apr 25, 2015 at 10:14:50PM +1000, Alexey Kardashevskiy wrote:
> > > > > > In order to support memory pre-registration, we need a way to track
> > > > > > the use of every registered memory region and only allow unregistration
> > > > > > if a region is not in use anymore. So we need a way to tell from what
> > > > > > region the just cleared TCE was from.
> > > > > >
> > > > > > This adds a userspace view of the TCE table into iommu_table struct.
> > > > > > It contains userspace address, one per TCE entry. The table is only
> > > > > > allocated when the ownership over an IOMMU group is taken which means
> > > > > > it is only used from outside of the powernv code (such as VFIO).
> > > > > >
> > > > > > Signed-off-by: Alexey Kardashevskiy <aik@xxxxxxxxx>
> > > > > > ---
> > > > > > Changes:
> > > > > > v9:
> > > > > > * fixed code flow in error cases added in v8
> > > > > >
> > > > > > v8:
> > > > > > * added ENOMEM on failed vzalloc()
> > > > > > ---
> > > > > >   arch/powerpc/include/asm/iommu.h          |  6 ++++++
> > > > > >   arch/powerpc/kernel/iommu.c               | 18 ++++++++++++++++++
> > > > > >   arch/powerpc/platforms/powernv/pci-ioda.c | 22 ++++++++++++++++++++--
> > > > > >   3 files changed, 44 insertions(+), 2 deletions(-)
> > > > > >
> > > > > > diff --git a/arch/powerpc/include/asm/iommu.h b/arch/powerpc/include/asm/iommu.h
> > > > > > index 7694546..1472de3 100644
> > > > > > --- a/arch/powerpc/include/asm/iommu.h
> > > > > > +++ b/arch/powerpc/include/asm/iommu.h
> > > > > > @@ -111,9 +111,15 @@ struct iommu_table {
> > > > > >   	unsigned long *it_map;       /* A simple allocation bitmap for now */
> > > > > >   	unsigned long  it_page_shift;/* table iommu page size */
> > > > > >   	struct iommu_table_group *it_table_group;
> > > > > > +	unsigned long *it_userspace; /* userspace view of the table */
> > > > >
> > > > > A single unsigned long doesn't seem like enough.
> > > >
> > > > Why single? This is an array.
> > >
> > > As in single per page.
> >
> >
> > Sorry, I am not following you here.
> > It is per IOMMU page. MAP/UNMAP work with IOMMU pages which are fully backed
> > with either system page or a huge page.
> >
> >
> > > > > How do you know
> > > > > which process's address space this address refers to?
> > > >
> > > > It is a current task. Multiple userspaces cannot use the same container/tables.
> > >
> > > Where is that enforced?
> >
> >
> > It is accessed from VFIO DMA map/unmap which are ioctls() to a container's
> > fd which is per a process.
>
> Usually, but what enforces that.  If you open a container fd, then
> fork(), and attempt to map from both parent and child, what happens?


vfio_group_fops::open() checks if the group is already opened, and I want 
to believe open() is called from fork() for new fd so no mapping can happen 
later.


--
Alexey
--
To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to majordomo@xxxxxxxxxxxxxxx
More majordomo info at  http://vger.kernel.org/majordomo-info.html
Please read the FAQ at  http://www.tux.org/lkml/