+ lib-test_hmm-use-device-devt-for-coherent-device-range-selection.patch added to mm-hotfixes-unstable branch

[Andrew Morton <akpm@linux-foundation.org>]

The patch titled
     Subject: lib: test_hmm: use device devt for coherent device range selection
has been added to the -mm mm-hotfixes-unstable branch.  Its filename is
     lib-test_hmm-use-device-devt-for-coherent-device-range-selection.patch

This patch will shortly appear at
     https://git.kernel.org/pub/scm/linux/kernel/git/akpm/25-new.git/tree/patches/lib-test_hmm-use-device-devt-for-coherent-device-range-selection.patch

This patch will later appear in the mm-hotfixes-unstable branch at
    git://git.kernel.org/pub/scm/linux/kernel/git/akpm/mm

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------------------------------------------------------
From: Stanislav Kinsburskii <skinsburskii@gmail.com>
Subject: lib: test_hmm: use device devt for coherent device range selection
Date: Mon, 29 Jun 2026 16:30:14 -0700

Commit af69016dab96 ("lib: test_hmm: implement a device release method")
moved the initial dmirror_allocate_chunk() call before cdev_device_add(). 
That means the struct cdev has not been added yet, so cdev_add() has not
initialized mdevice->cdevice.dev.

The coherent-device range selection uses the device minor to choose
between spm_addr_dev0 and spm_addr_dev1.  Reading
MINOR(mdevice->cdevice.dev) before cdev_add() therefore always sees an
uninitialized dev_t.  As a result, both coherent devices select the same
physical range, and adding the second device fails due to the overlapping
dev_pagemap range.

Use mdevice->device.devt instead.  It is initialized in
dmirror_device_init() before dmirror_allocate_chunk() is called and is the
same dev_t later passed to cdev_device_add().

Link: https://lore.kernel.org/178277581197.172200.16265155329935822153.stgit@skinsburskii
Fixes: af69016dab96 ("lib: test_hmm: implement a device release method")
Signed-off-by: Stanislav Kinsburskii <skinsburskii@gmail.com>
Cc: Alistair Popple <apopple@nvidia.com>
Cc: Balbir Singh <balbirs@nvidia.com>
Cc: Zenghui Yu (Huawei) <zenghui.yu@linux.dev>
Cc: Jason Gunthorpe <jgg@ziepe.ca>
Cc: Leon Romanovsky <leon@kernel.org>
Cc: <stable@vger.kernel.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
---

 lib/test_hmm.c |    2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

--- a/lib/test_hmm.c~lib-test_hmm-use-device-devt-for-coherent-device-range-selection
+++ a/lib/test_hmm.c
@@ -581,7 +581,7 @@ static int dmirror_allocate_chunk(struct
 		devmem->pagemap.type = MEMORY_DEVICE_PRIVATE;
 		break;
 	case HMM_DMIRROR_MEMORY_DEVICE_COHERENT:
-		devmem->pagemap.range.start = (MINOR(mdevice->cdevice.dev) - 2) ?
+		devmem->pagemap.range.start = (MINOR(mdevice->device.devt) - 2) ?
 							spm_addr_dev0 :
 							spm_addr_dev1;
 		devmem->pagemap.range.end = devmem->pagemap.range.start +
_

Patches currently in -mm which might be from skinsburskii@gmail.com are

lib-test_hmm-use-device-devt-for-coherent-device-range-selection.patch