Re: [Xen-devel] [PATCH 5/6] xen-gntalloc: Userspace grant allocation driver

[Daniel De Graaf <dgdegra@xxxxxxxxxxxxx>]

On 01/27/2011 02:23 PM, Konrad Rzeszutek Wilk wrote:
> On Thu, Jan 27, 2011 at 01:52:10PM -0500, Konrad Rzeszutek Wilk wrote:
>> On Fri, Jan 21, 2011 at 10:59:07AM -0500, Daniel De Graaf wrote:
>>> This allows a userspace application to allocate a shared page for
>>> implementing inter-domain communication or device drivers. These
>>> shared pages can be mapped using the gntdev device or by the kernel
>>> in another domain.
>>>
>>> Signed-off-by: Daniel De Graaf <dgdegra@xxxxxxxxxxxxx>
>>> ---
>>>  drivers/xen/Kconfig    |    8 +
>>>  drivers/xen/Makefile   |    2 +
>>>  drivers/xen/gntalloc.c |  477 
>>> ++++++++++++++++++++++++++++++++++++++++++++++++
>>>  include/xen/gntalloc.h |   70 +++++++
>>>  4 files changed, 557 insertions(+), 0 deletions(-)
>>>  create mode 100644 drivers/xen/gntalloc.c
>>>  create mode 100644 include/xen/gntalloc.h
>>>
>>> diff --git a/drivers/xen/Kconfig b/drivers/xen/Kconfig
>>> index 07bec09..a3d7afb 100644
>>> --- a/drivers/xen/Kconfig
>>> +++ b/drivers/xen/Kconfig
>>> @@ -80,6 +80,14 @@ config XEN_GNTDEV
>>>     help
>>>       Allows userspace processes to use grants.
>>>  
>>> +config XEN_GRANT_DEV_ALLOC
>>> +   tristate "User-space grant reference allocator driver"
>>> +   depends on XEN
>>> +   help
>>> +     Allows userspace processes to create pages with access granted
>>> +     to other domains. This can be used to implement frontend drivers
>>> +     or as part of an inter-domain shared memory channel.
> 
> 
>>> +
>>>  config XEN_PLATFORM_PCI
>>>     tristate "xen platform pci device driver"
>>>     depends on XEN_PVHVM && PCI
>>> diff --git a/drivers/xen/Makefile b/drivers/xen/Makefile
>>> index 5088cc2..9585a1d 100644
>>> --- a/drivers/xen/Makefile
>>> +++ b/drivers/xen/Makefile
>>> @@ -10,6 +10,7 @@ obj-$(CONFIG_XEN_XENCOMM) += xencomm.o
>>>  obj-$(CONFIG_XEN_BALLOON)  += balloon.o
>>>  obj-$(CONFIG_XEN_DEV_EVTCHN)       += xen-evtchn.o
>>>  obj-$(CONFIG_XEN_GNTDEV)   += xen-gntdev.o
>>> +obj-$(CONFIG_XEN_GRANT_DEV_ALLOC)  += xen-gntalloc.o
>>>  obj-$(CONFIG_XENFS)                += xenfs/
>>>  obj-$(CONFIG_XEN_SYS_HYPERVISOR)   += sys-hypervisor.o
>>>  obj-$(CONFIG_XEN_PLATFORM_PCI)     += xen-platform-pci.o
>>> @@ -18,5 +19,6 @@ obj-$(CONFIG_XEN_DOM0)            += pci.o
>>>  
>>>  xen-evtchn-y                       := evtchn.o
>>>  xen-gntdev-y                               := gntdev.o
>>> +xen-gntalloc-y                             := gntalloc.o
>>>  
>>>  xen-platform-pci-y         := platform-pci.o
>>> diff --git a/drivers/xen/gntalloc.c b/drivers/xen/gntalloc.c
>>> new file mode 100644
>>> index 0000000..a230dc4
>>> --- /dev/null
>>> +++ b/drivers/xen/gntalloc.c
>>> @@ -0,0 +1,477 @@
>>> +/******************************************************************************
>>> + * gntalloc.c
>>> + *
>>> + * Device for creating grant references (in user-space) that may be shared
>>> + * with other domains.
>>> + *
>>> + * This program is distributed in the hope that it will be useful,
>>> + * but WITHOUT ANY WARRANTY; without even the implied warranty of
>>> + * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
>>> + * GNU General Public License for more details.
>>> + *
>>> + * You should have received a copy of the GNU General Public License
>>> + * along with this program; if not, write to the Free Software
>>> + * Foundation, Inc., 59 Temple Place, Suite 330, Boston, MA  02111-1307  
>>> USA
>>> + */
>>> +
>>> +/*
>>> + * This driver exists to allow userspace programs in Linux to allocate 
>>> kernel
>>> + * memory that will later be shared with another domain.  Without this 
>>> device,
>>> + * Linux userspace programs cannot create grant references.
> 
> Why can't this be done in gntdev? Is there a simple test program for this?
> 

I didn't do this in gntdev so that it would be possible to allow programs to map
grants without also giving them rights to allocate (or vice versa). The actions
taken on the pages are also different (gntdev remaps them, gntalloc just shares)
so much of the surrounding map/unmap logic is different.

If it's preferred, I could try to add the ioctls to gntdev; there is some 
overlap
in functionality, especially when using the HVM code in gntdev. The limits for
gntalloc need to remain different, because a page allocated by gntalloc is
impossible to reclaim using the OOM killer (unlike pages allocated by gntdev).

Simple test program (for gntdev and gntalloc) attached.

-- 
Daniel De Graaf
National Security Agency

Attachment: test_gnt.c
Description: Text document

_______________________________________________
Xen-devel mailing list
Xen-devel@xxxxxxxxxxxxxxxxxxx
http://lists.xensource.com/xen-devel