On 11.08.20 11:44, Roger Pau Monne wrote:
To be used in order to create foreign mappings. This is based on the ZONE_DEVICE facility which is used by persistent memory devices in order to create struct pages and kernel virtual mappings for the IOMEM areas of such devices. Note that on kernels without support for ZONE_DEVICE Xen will fallback to use ballooned pages in order to create foreign mappings.
The newly added helpers use the same parameters as the existing {alloc/free}_xenballooned_pages functions, which allows for in-place replacement of the callers. Once a memory region has been added to be used as scratch mapping space it will no longer be released, and pages returned are kept in a linked list. This allows to have a buffer of pages and prevents resorting to frequent additions and removals of regions.
If enabled (because ZONE_DEVICE is supported) the usage of the new functionality untangles Xen balloon and RAM hotplug from the usage of unpopulated physical memory ranges to map foreign pages, which is the correct thing to do in order to avoid mappings of foreign pages depend on memory hotplug.
Note the driver is currently not enabled on Arm platforms because it would interfere with the identity mapping required on some platforms.
Signed-off-by: Roger Pau Monné roger.pau@citrix.com
Cc: Oleksandr Andrushchenko oleksandr_andrushchenko@epam.com Cc: David Airlie airlied@linux.ie Cc: Daniel Vetter daniel@ffwll.ch Cc: Boris Ostrovsky boris.ostrovsky@oracle.com Cc: Juergen Gross jgross@suse.com Cc: Stefano Stabellini sstabellini@kernel.org Cc: Dan Carpenter dan.carpenter@oracle.com Cc: Roger Pau Monne roger.pau@citrix.com Cc: Wei Liu wl@xen.org Cc: Yan Yankovskyi yyankovskyi@gmail.com Cc: dri-devel@lists.freedesktop.org Cc: xen-devel@lists.xenproject.org Cc: linux-mm@kvack.org Cc: David Hildenbrand david@redhat.com Cc: Michal Hocko mhocko@kernel.org Cc: Dan Williams dan.j.williams@intel.com
Changes since v3:
- Introduce a Kconfig option that gates the addition of the unpopulated alloc driver. This allows to easily disable it on Arm platforms.
- Dropped Juergen RB due to the addition of the Kconfig option.
- Switched from MEMORY_DEVICE_DEVDAX to MEMORY_DEVICE_GENERIC.
Changes since v2:
- Drop BUILD_BUG_ON regarding PVMMU page sizes.
- Use a SPDX license identifier.
- Call fill with only the minimum required number of pages.
- Include xen.h header in xen_drm_front_gem.c.
- Use less generic function names.
- Exit early from the init function if not a PV guest.
- Don't use all caps for region name.
drivers/gpu/drm/xen/xen_drm_front_gem.c | 9 +- drivers/xen/Kconfig | 4 + drivers/xen/Makefile | 1 + drivers/xen/balloon.c | 4 +- drivers/xen/grant-table.c | 4 +- drivers/xen/privcmd.c | 4 +- drivers/xen/unpopulated-alloc.c | 185 ++++++++++++++++++++++++ drivers/xen/xenbus/xenbus_client.c | 6 +- drivers/xen/xlate_mmu.c | 4 +- include/xen/xen.h | 9 ++ 10 files changed, 215 insertions(+), 15 deletions(-) create mode 100644 drivers/xen/unpopulated-alloc.c
diff --git a/drivers/xen/Kconfig b/drivers/xen/Kconfig index 1d339ef92422..018020b91baa 100644 --- a/drivers/xen/Kconfig +++ b/drivers/xen/Kconfig @@ -327,4 +327,8 @@ config XEN_HAVE_VPMU config XEN_FRONT_PGDIR_SHBUF tristate
+config XEN_UNPOPULATED_ALLOC
- bool
- default y if ZONE_DEVICE && !ARM && !ARM64
There is a current effort to enable Xen on RISC-V. Do we expect this option to be usable for this architecture? If yes, I'm fine with the exclusion of Arm, otherwise I'd opt for defaulting to yes only for X86.
Either way you can have my:
Reviewed-by: Juergen Gross jgross@suse.com
Juergen