On Thu, Jan 24, 2019 at 03:14:44PM -0800, Dave Hansen wrote:
>
> From: Dave Hansen <dave.hansen@xxxxxxxxxxxxxxx>
>
> HMM consumes physical address space for its own use, even
> though nothing is mapped or accessible there. It uses a
> special resource description (IORES_DESC_DEVICE_PRIVATE_MEMORY)
> to uniquely identify these areas.
>
> When HMM consumes address space, it makes a best guess about
> what to consume. However, it is possible that a future memory
> or device hotplug can collide with the reserved area. In the
> case of these conflicts, there is an error message in
> register_memory_resource().
>
> Later patches in this series move register_memory_resource()
> from using request_resource_conflict() to __request_region().
> Unfortunately, __request_region() does not return the conflict
> like the previous function did, which makes it impossible to
> check for IORES_DESC_DEVICE_PRIVATE_MEMORY in a conflicting
> resource.
>
> Instead of warning in register_memory_resource(), move the
> check into the core resource code itself (__request_region())
> where the conflicting resource _is_ available. This has the
> added bonus of producing a warning in case of HMM conflicts
> with devices *or* RAM address space, as opposed to the RAM-
> only warnings that were there previously.
>
> Signed-off-by: Dave Hansen <dave.hansen@xxxxxxxxxxxxxxx>
> Cc: Dan Williams <dan.j.williams@xxxxxxxxx>
> Cc: Dave Jiang <dave.jiang@xxxxxxxxx>
> Cc: Ross Zwisler <zwisler@xxxxxxxxxx>
> Cc: Vishal Verma <vishal.l.verma@xxxxxxxxx>
> Cc: Tom Lendacky <thomas.lendacky@xxxxxxx>
> Cc: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>
> Cc: Michal Hocko <mhocko@xxxxxxxx>
> Cc: linux-nvdimm@xxxxxxxxxxxx
> Cc: linux-kernel@xxxxxxxxxxxxxxx
> Cc: linux-mm@xxxxxxxxx
> Cc: Huang Ying <ying.huang@xxxxxxxxx>
> Cc: Fengguang Wu <fengguang.wu@xxxxxxxxx>
Reviewed-by: Jerome Glisse <jglisse@xxxxxxxxxx>
> ---
>
> b/kernel/resource.c | 10 ++++++++++
> b/mm/memory_hotplug.c | 5 -----
> 2 files changed, 10 insertions(+), 5 deletions(-)
>
> diff -puN kernel/resource.c~move-request_region-check kernel/resource.c
> --- a/kernel/resource.c~move-request_region-check 2019-01-24 15:13:14.453199539 -0800
> +++ b/kernel/resource.c 2019-01-24 15:13:14.458199539 -0800
> @@ -1123,6 +1123,16 @@ struct resource * __request_region(struc
> conflict = __request_resource(parent, res);
> if (!conflict)
> break;
> + /*
> + * mm/hmm.c reserves physical addresses which then
> + * become unavailable to other users. Conflicts are
> + * not expected. Be verbose if one is encountered.
> + */
> + if (conflict->desc == IORES_DESC_DEVICE_PRIVATE_MEMORY) {
> + pr_debug("Resource conflict with unaddressable "
> + "device memory at %#010llx !\n",
> + (unsigned long long)start);
> + }
> if (conflict != parent) {
> if (!(conflict->flags & IORESOURCE_BUSY)) {
> parent = conflict;
> diff -puN mm/memory_hotplug.c~move-request_region-check mm/memory_hotplug.c
> --- a/mm/memory_hotplug.c~move-request_region-check 2019-01-24 15:13:14.455199539 -0800
> +++ b/mm/memory_hotplug.c 2019-01-24 15:13:14.459199539 -0800
> @@ -109,11 +109,6 @@ static struct resource *register_memory_
> 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);
> return ERR_PTR(-EEXIST);
> _
