linux-kernel - [PATCH 2/5] mm/resource: move HMM pr

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Message-Id: <20190124231444.38182DD8@viggo.jf.intel.com>
Date:   Thu, 24 Jan 2019 15:14:44 -0800
From:   Dave Hansen <dave.hansen@...ux.intel.com>
To:     linux-kernel@...r.kernel.org
Cc:     Dave Hansen <dave.hansen@...ux.intel.com>,
        dan.j.williams@...el.com, dave.jiang@...el.com, zwisler@...nel.org,
        vishal.l.verma@...el.com, thomas.lendacky@....com,
        akpm@...ux-foundation.org, mhocko@...e.com,
        linux-nvdimm@...ts.01.org, linux-mm@...ck.org,
        ying.huang@...el.com, fengguang.wu@...el.com, jglisse@...hat.com
Subject: [PATCH 2/5] mm/resource: move HMM pr_debug() deeper into resource code


From: Dave Hansen <dave.hansen@...ux.intel.com>

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@...ux.intel.com>
Cc: Dan Williams <dan.j.williams@...el.com>
Cc: Dave Jiang <dave.jiang@...el.com>
Cc: Ross Zwisler <zwisler@...nel.org>
Cc: Vishal Verma <vishal.l.verma@...el.com>
Cc: Tom Lendacky <thomas.lendacky@....com>
Cc: Andrew Morton <akpm@...ux-foundation.org>
Cc: Michal Hocko <mhocko@...e.com>
Cc: linux-nvdimm@...ts.01.org
Cc: linux-kernel@...r.kernel.org
Cc: linux-mm@...ck.org
Cc: Huang Ying <ying.huang@...el.com>
Cc: Fengguang Wu <fengguang.wu@...el.com>
Cc: Jerome Glisse <jglisse@...hat.com>
---

 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);
_