linux-kernel - [PATCH] lib/test_hmm: reduce stack usage

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Message-Id: <20250610092159.2639515-1-arnd@kernel.org>
Date: Tue, 10 Jun 2025 11:21:50 +0200
From: Arnd Bergmann <arnd@...nel.org>
To: Andrew Morton <akpm@...ux-foundation.org>,
	Jérôme Glisse <jglisse@...hat.com>
Cc: Arnd Bergmann <arnd@...db.de>,
	David Hildenbrand <david@...hat.com>,
	Alistair Popple <apopple@...dia.com>,
	Jason Gunthorpe <jgg@...pe.ca>,
	Thorsten Blum <thorsten.blum@...ux.dev>,
	Jeff Johnson <jeff.johnson@....qualcomm.com>,
	linux-mm@...ck.org,
	linux-kernel@...r.kernel.org
Subject: [PATCH] lib/test_hmm: reduce stack usage

From: Arnd Bergmann <arnd@...db.de>

The various test ioctl handlers use arrays of 64 integers that add up to 1KiB
of stack data, which in turn leads to exceeding the warning limit in some
configurations:

lib/test_hmm.c:935:12: error: stack frame size (1408) exceeds limit (1280) in 'dmirror_migrate_to_device' [-Werror,-Wframe-larger-than]

Use half the size for these arrays, in order to stay under the warning limits.
The code can already deal with arbitrary lengths, but this may be a little less
efficient.

Signed-off-by: Arnd Bergmann <arnd@...db.de>
---
 lib/test_hmm.c | 14 +++++++-------
 1 file changed, 7 insertions(+), 7 deletions(-)

diff --git a/lib/test_hmm.c b/lib/test_hmm.c
index 5b144bc5c4ec..761725bc713c 100644
--- a/lib/test_hmm.c
+++ b/lib/test_hmm.c
@@ -330,7 +330,7 @@ static int dmirror_fault(struct dmirror *dmirror, unsigned long start,
 {
 	struct mm_struct *mm = dmirror->notifier.mm;
 	unsigned long addr;
-	unsigned long pfns[64];
+	unsigned long pfns[32];
 	struct hmm_range range = {
 		.notifier = &dmirror->notifier,
 		.hmm_pfns = pfns,
@@ -879,8 +879,8 @@ static int dmirror_migrate_to_system(struct dmirror *dmirror,
 	unsigned long size = cmd->npages << PAGE_SHIFT;
 	struct mm_struct *mm = dmirror->notifier.mm;
 	struct vm_area_struct *vma;
-	unsigned long src_pfns[64] = { 0 };
-	unsigned long dst_pfns[64] = { 0 };
+	unsigned long src_pfns[32] = { 0 };
+	unsigned long dst_pfns[32] = { 0 };
 	struct migrate_vma args = { 0 };
 	unsigned long next;
 	int ret;
@@ -939,8 +939,8 @@ static int dmirror_migrate_to_device(struct dmirror *dmirror,
 	unsigned long size = cmd->npages << PAGE_SHIFT;
 	struct mm_struct *mm = dmirror->notifier.mm;
 	struct vm_area_struct *vma;
-	unsigned long src_pfns[64] = { 0 };
-	unsigned long dst_pfns[64] = { 0 };
+	unsigned long src_pfns[32] = { 0 };
+	unsigned long dst_pfns[32] = { 0 };
 	struct dmirror_bounce bounce;
 	struct migrate_vma args = { 0 };
 	unsigned long next;
@@ -1144,8 +1144,8 @@ static int dmirror_snapshot(struct dmirror *dmirror,
 	unsigned long size = cmd->npages << PAGE_SHIFT;
 	unsigned long addr;
 	unsigned long next;
-	unsigned long pfns[64];
-	unsigned char perm[64];
+	unsigned long pfns[32];
+	unsigned char perm[32];
 	char __user *uptr;
 	struct hmm_range range = {
 		.hmm_pfns = pfns,
-- 
2.39.5