patches/old/mm-shmem-update-shmem-to-use-mmap_prepare.patch

From: Lorenzo Stoakes <lorenzo.stoakes@oracle.com>
Subject: mm/shmem: update shmem to use mmap_prepare
Date: Wed, 17 Sep 2025 20:11:03 +0100

Patch series "expand mmap_prepare functionality, port more users", v4.

Since commit c84bf6dd2b83 ("mm: introduce new .mmap_prepare() file
callback"), The f_op->mmap hook has been deprecated in favour of
f_op->mmap_prepare.

This was introduced in order to make it possible for us to eventually
eliminate the f_op->mmap hook which is highly problematic as it allows
drivers and filesystems raw access to a VMA which is not yet correctly
initialised.

This hook also introduced complexity for the memory mapping operation, as
we must correctly unwind what we do should an error arises.

Overall this interface being so open has caused significant problems for
us, including security issues, it is important for us to simply eliminate
this as a source of problems.

Therefore this series continues what was established by extending the
functionality further to permit more drivers and filesystems to use
mmap_prepare.

We start by udpating some existing users who can use the mmap_prepare
functionality as-is.

We then introduce the concept of an mmap 'action', which a user, on
mmap_prepare, can request to be performed upon the VMA:

* Nothing - default, we're done
* Remap PFN - perform PFN remap with specified parameters
* I/O remap PFN - perform I/O PFN remap with specified parameters

By setting the action in mmap_prepare, this allows us to dynamically decide
what to do next, so if a driver/filesystem needs to determine whether to
e.g. remap or use a mixed map, it can do so then change which is done.

This significantly expands the capabilities of the mmap_prepare hook, while
maintaining as much control as possible in the mm logic.

We split [io_]remap_pfn_range*() functions which allow for PFN remap (a
typical mapping prepopulation operation) split between a prepare/complete
step, as well as io_mremap_pfn_range_prepare, complete for a similar
purpose.

From there we update various mm-adjacent logic to use this functionality as
a first set of changes.

We also add success and error hooks for post-action processing for e.g. 
output debug log on success and filtering error codes.


This patch (of 14):

This simply assigns the vm_ops so is easily updated - do so.

Link: https://lkml.kernel.org/r/cover.1758135681.git.lorenzo.stoakes@oracle.com
Link: https://lkml.kernel.org/r/86029a4f59733826c8419e48f6ad4000932a6d08.1758135681.git.lorenzo.stoakes@oracle.com
Signed-off-by: Lorenzo Stoakes <lorenzo.stoakes@oracle.com>
Reviewed-by: Baolin Wang <baolin.wang@linux.alibaba.com>
Reviewed-by: David Hildenbrand <david@redhat.com>
Reviewed-by: Jan Kara <jack@suse.cz>
Reviewed-by: Jason Gunthorpe <jgg@nvidia.com>
Reviewed-by: Pedro Falcato <pfalcato@suse.de>
Cc: Alexander Gordeev <agordeev@linux.ibm.com>
Cc: Al Viro <viro@zeniv.linux.org.uk>
Cc: Andreas Larsson <andreas@gaisler.com>
Cc: Andrey Konovalov <andreyknvl@gmail.com>
Cc: Arnd Bergmann <arnd@arndb.de>
Cc: Baoquan He <bhe@redhat.com>
Cc: Chatre, Reinette <reinette.chatre@intel.com>
Cc: Christian Borntraeger <borntraeger@linux.ibm.com>
Cc: Christian Brauner <brauner@kernel.org>
Cc: Dan Williams <dan.j.williams@intel.com>
Cc: Dave Jiang <dave.jiang@intel.com>
Cc: Dave Martin <dave.martin@arm.com>
Cc: Dave Young <dyoung@redhat.com>
Cc: David S. Miller <davem@davemloft.net>
Cc: Dmitriy Vyukov <dvyukov@google.com>
Cc: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Cc: Guo Ren <guoren@kernel.org>
Cc: Heiko Carstens <hca@linux.ibm.com>
Cc: Hugh Dickins <hughd@google.com>
Cc: James Morse <james.morse@arm.com>
Cc: Jann Horn <jannh@google.com>
Cc: Jonathan Corbet <corbet@lwn.net>
Cc: Kevin Tian <kevin.tian@intel.com>
Cc: Konstantin Komarov <almaz.alexandrovich@paragon-software.com>
Cc: Liam Howlett <liam.howlett@oracle.com>
Cc: "Luck, Tony" <tony.luck@intel.com>
Cc: Matthew Wilcox (Oracle) <willy@infradead.org>
Cc: Michal Hocko <mhocko@suse.com>
Cc: Mike Rapoport <rppt@kernel.org>
Cc: Muchun Song <muchun.song@linux.dev>
Cc: Nicolas Pitre <nico@fluxnic.net>
Cc: Oscar Salvador <osalvador@suse.de>
Cc: Robin Murohy <robin.murphy@arm.com>
Cc: Suren Baghdasaryan <surenb@google.com>
Cc: Sven Schnelle <svens@linux.ibm.com>
Cc: Thomas Bogendoerfer <tsbogend@alpha.franken.de>
Cc: "Uladzislau Rezki (Sony)" <urezki@gmail.com>
Cc: Vasily Gorbik <gor@linux.ibm.com>
Cc: Vishal Verma <vishal.l.verma@intel.com>
Cc: Vivek Goyal <vgoyal@redhat.com>
Cc: Vlastimil Babka <vbabka@suse.cz>
Cc: Will Deacon <will@kernel.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
---

 mm/shmem.c |    9 +++++----
 1 file changed, 5 insertions(+), 4 deletions(-)

--- a/mm/shmem.c~mm-shmem-update-shmem-to-use-mmap_prepare
+++ a/mm/shmem.c
@@ -2924,16 +2924,17 @@ out_nomem:
 	return retval;
 }
 
-static int shmem_mmap(struct file *file, struct vm_area_struct *vma)
+static int shmem_mmap_prepare(struct vm_area_desc *desc)
 {
+	struct file *file = desc->file;
 	struct inode *inode = file_inode(file);
 
 	file_accessed(file);
 	/* This is anonymous shared memory if it is unlinked at the time of mmap */
 	if (inode->i_nlink)
-		vma->vm_ops = &shmem_vm_ops;
+		desc->vm_ops = &shmem_vm_ops;
 	else
-		vma->vm_ops = &shmem_anon_vm_ops;
+		desc->vm_ops = &shmem_anon_vm_ops;
 	return 0;
 }
 
@@ -5203,7 +5204,7 @@ static const struct address_space_operat
 };
 
 static const struct file_operations shmem_file_operations = {
-	.mmap		= shmem_mmap,
+	.mmap_prepare	= shmem_mmap_prepare,
 	.open		= shmem_file_open,
 	.get_unmapped_area = shmem_get_unmapped_area,
 #ifdef CONFIG_TMPFS
_