On Wed, Jan 16, 2019 at 10:19:02AM -0800, Dave Hansen wrote:
>
> From: Dave Hansen <dave.han...@linux.intel.com>
>
> The mm/resource.c code is used to manage the physical address
> space. We can view the current resource configuration in
> /proc/iomem. An example of this is at the bottom of this
> description.
>
> The nvdimm subsystem "owns" the physical address resources which
> map to persistent memory and has resources inserted for them as
> "Persistent Memory". We want to use this persistent memory, but
> as volatile memory, just like RAM. The best way to do this is
> to leave the existing resource in place, but add a "System RAM"
> resource underneath it. This clearly communicates the ownership
> relationship of this memory.
>
> The request_resource_conflict() API only deals with the
> top-level resources. Replace it with __request_region() which
> will search for !IORESOURCE_BUSY areas lower in the resource
> tree than the top level.
>
> We also rework the old error message a bit since we do not get
> the conflicting entry back: only an indication that we *had* a
> conflict.
We should keep the device private check (moving it in __request_region)
as device private can try to register un-use physical address (un-use
at time of device private registration) that latter can block valid
physical address the error message you are removing report such event.
>
> We *could* also simply truncate the existing top-level
> "Persistent Memory" resource and take over the released address
> space. But, this means that if we ever decide to hot-unplug the
> "RAM" and give it back, we need to recreate the original setup,
> which may mean going back to the BIOS tables.
>
> This should have no real effect on the existing collision
> detection because the areas that truly conflict should be marked
> IORESOURCE_BUSY.
Still i am worrying that this might allow device private to register
itself as a child of some un-busy resource as this patch obviously
change the behavior of register_memory_resource()
What about instead explicitly providing parent resource to add_memory()
and then to register_memory_resource() so if it is provided as an
argument (!NULL) then you can __request_region(arg_res, ...) otherwise
you keep existing code intact ?
Cheers,
Jérôme
>
> 00000000-00000fff : Reserved
> 00001000-0009fbff : System RAM
> 0009fc00-0009ffff : Reserved
> 000a0000-000bffff : PCI Bus 0000:00
> 000c0000-000c97ff : Video ROM
> 000c9800-000ca5ff : Adapter ROM
> 000f0000-000fffff : Reserved
> 000f0000-000fffff : System ROM
> 00100000-9fffffff : System RAM
> 01000000-01e071d0 : Kernel code
> 01e071d1-027dfdff : Kernel data
> 02dc6000-0305dfff : Kernel bss
> a0000000-afffffff : Persistent Memory (legacy)
> a0000000-a7ffffff : System RAM
> b0000000-bffdffff : System RAM
> bffe0000-bfffffff : Reserved
> c0000000-febfffff : PCI Bus 0000:00
>
> Cc: Dan Williams <dan.j.willi...@intel.com>
> Cc: Dave Jiang <dave.ji...@intel.com>
> Cc: Ross Zwisler <zwis...@kernel.org>
> Cc: Vishal Verma <vishal.l.ve...@intel.com>
> Cc: Tom Lendacky <thomas.lenda...@amd.com>
> Cc: Andrew Morton <a...@linux-foundation.org>
> Cc: Michal Hocko <mho...@suse.com>
> Cc: linux-nvd...@lists.01.org
> Cc: linux-kernel@vger.kernel.org
> Cc: linux...@kvack.org
> Cc: Huang Ying <ying.hu...@intel.com>
> Cc: Fengguang Wu <fengguang...@intel.com>
>
> Signed-off-by: Dave Hansen <dave.han...@linux.intel.com>
> ---
>
> b/mm/memory_hotplug.c | 31 ++++++++++++++-----------------
> 1 file changed, 14 insertions(+), 17 deletions(-)
>
> diff -puN
> mm/memory_hotplug.c~mm-memory-hotplug-allow-memory-resource-to-be-child
> mm/memory_hotplug.c
> --- a/mm/memory_hotplug.c~mm-memory-hotplug-allow-memory-resource-to-be-child
> 2018-12-20 11:48:42.317771933 -0800
> +++ b/mm/memory_hotplug.c 2018-12-20 11:48:42.322771933 -0800
> @@ -98,24 +98,21 @@ void mem_hotplug_done(void)
> /* add this memory to iomem resource */
> static struct resource *register_memory_resource(u64 start, u64 size)
> {
> - struct resource *res, *conflict;
> - res = kzalloc(sizeof(struct resource), GFP_KERNEL);
> - if (!res)
> - return ERR_PTR(-ENOMEM);
> + struct resource *res;
> + unsigned long flags = IORESOURCE_SYSTEM_RAM | IORESOURCE_BUSY;
> + char *resource_name = "System RAM";
>
> - res->name = "System RAM";
> - res->start = start;
> - res->end = start + size - 1;
> - res->flags = IORESOURCE_SYSTEM_RAM | IORESOURCE_BUSY;
> - conflict = request_resource_conflict(&iomem_resource, res);
> - if (conflict) {
> - if (conflict->desc == IORES_DESC_DEVICE_PRIVATE_MEMORY) {
> - pr_debug("Device unaddressable memory block "
> - "memory hotplug at %#010llx !\n",
> - (unsigned long long)start);
> - }
> - pr_debug("System RAM resource %pR cannot be added\n", res);
> - kfree(res);
> + /*
> + * Request ownership of the new memory range. This might be
> + * a child of an existing resource that was present but
> + * not marked as busy.
> + */
> + res = __request_region(&iomem_resource, start, size,
> + resource_name, flags);
> +
> + if (!res) {
> + pr_debug("Unable to reserve System RAM region:
> %016llx->%016llx\n",
> + start, start + size);
> return ERR_PTR(-EEXIST);
> }
> return res;
> _
>
