[merged mm-stable] scsi-sg-convert-mmap-hook-to-mmap_prepare-and-rework.patch removed from -mm tree

[merged mm-stable] scsi-sg-convert-mmap-hook-to-mmap_prepare-and-rework.patch removed from -mm tree

[Andrew Morton]

The quilt patch titled
     Subject: scsi: sg: convert mmap hook to mmap_prepare and rework
has been removed from the -mm tree.  Its filename was
     scsi-sg-convert-mmap-hook-to-mmap_prepare-and-rework.patch

This patch was dropped because it was merged into the mm-stable branch
of git://git.kernel.org/pub/scm/linux/kernel/git/akpm/mm

------------------------------------------------------
From: "Lorenzo Stoakes (ARM)" <ljs@kernel.org>
Subject: scsi: sg: convert mmap hook to mmap_prepare and rework
Date: Tue, 13 Oct 2026 16:04:58 +0100

Move from the deprecated mmap hook to the new mmap_prepare hook.

We are mapping kernel pages here, so use the discontiguous kernel mapping
mmap action to do so.

Unwind the rather confusing loop and instead map as many pages as we can at
one time.

Note that we do not need to pay attention to rsv_schp->k_use_sg here, as
the pages are populated for the length of the buffer at
rsv_schp->page_order granularity as compound pages.

The discontiguous kernel page mapping logic handles the compound pages for
us.

sfp->mmap_called keeps the buffer stable for us. As before it is never
cleared, so a failed mmap also leaves it set.

We also remove some useless vma, vma->vm_file NULL checks - these will
always be non-NULL if you reached the mmap hook logic.

We retain log output for consistency, but change what's output on page
mapping to indicate that sg_discontig_get() does the work now.

Note that we drop the VMA_IO_BIT flag for the VMA here. It was never
necessary as we invoke alloc_pages() which gives us refcounted folios that
are fine for GUP to access (VMA_IO_BIT would prevent that).

Link: https://lore.kernel.org/20261013-b4-mmap-prepare-vma-flag-sanify-v6-18-1aa3c9b139f9@kernel.org
Signed-off-by: Lorenzo Stoakes (ARM) <ljs@kernel.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Reviewed-by: Suren Baghdasaryan <surenb@google.com>
Cc: Liam R. Howlett <liam@infradead.org>
Cc: Vlastimil Babka <vbabka@kernel.org>
Cc: Jann Horn <jannh@google.com>
Cc: Pedro Falcato <pfalcato@suse.de>
Cc: David Hildenbrand <david@kernel.org>
Cc: Mike Rapoport <rppt@kernel.org>
Cc: Michal Hocko <mhocko@suse.com>
Cc: Jonathan Corbet <corbet@lwn.net>
Cc: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Cc: Dennis Dalessandro <dennis.dalessandro@cornelisnetworks.com>
Cc: Jason Gunthorpe <jgg@ziepe.ca>
Cc: Leon Romanovsky <leon@kernel.org>
Cc: Paul Moore <paul@paul-moore.com>
Cc: Stephen Smalley <stephen.smalley.work@gmail.com>
Cc: Jaroslav Kysela <perex@perex.cz>
Cc: Takashi Iwai <tiwai@suse.com>
Cc: Alexei Starovoitov <ast@kernel.org>
Cc: Daniel Borkmann <daniel@iogearbox.net>
Cc: Andrii Nakryiko <andrii@kernel.org>
Cc: Eduard Zingerman <eddyz87@gmail.com>
Cc: Kumar Kartikeya Dwivedi <memxor@gmail.com>
Cc: Zi Yan <ziy@nvidia.com>
Cc: Baolin Wang <baolin.wang@linux.alibaba.com>
Cc: Nico Pache <nico.pache@linux.dev>
Cc: Ryan Roberts <ryan.roberts@arm.com>
Cc: Dev Jain <dev.jain@arm.com>
Cc: Barry Song <baohua@kernel.org>
Cc: Lance Yang <lance.yang@linux.dev>
Cc: Usama Arif <usama.arif@linux.dev>
Cc: Kiryl Shutsemau <kas@kernel.org>
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Cc: Namhyung Kim <namhyung@kernel.org>
Cc: Mark Rutland <mark.rutland@arm.com>
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Cc: Harry Yoo <harry@kernel.org>
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Cc: Will Deacon <will@kernel.org>
Cc: Aneesh Kumar K.V <aneesh.kumar@kernel.org>
Cc: Nicholas Piggin <npiggin@gmail.com>
Cc: Arnd Bergmann <arnd@arndb.de>
Cc: Muchun Song <muchun.song@linux.dev>
Cc: Oscar Salvador <osalvador@suse.de>
Cc: Matthew Wilcox (Oracle) <willy@infradead.org>
Cc: Jan Kara <jack@suse.cz>
Cc: Marc Zyngier <maz@kernel.org>
Cc: Oliver Upton <oupton@kernel.org>
Cc: Catalin Marinas <catalin.marinas@arm.com>
Cc: Madhavan Srinivasan <maddy@linux.ibm.com>
Cc: Anup Patel <anup@brainfault.org>
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Cc: Albert Ou <aou@eecs.berkeley.edu>
Cc: Christian Borntraeger <borntraeger@linux.ibm.com>
Cc: Janosch Frank <frankja@linux.ibm.com>
Cc: Claudio Imbrenda <imbrenda@linux.ibm.com>
Cc: Alexander Gordeev <agordeev@linux.ibm.com>
Cc: Gerald Schaefer <gerald.schaefer@linux.ibm.com>
Cc: Heiko Carstens <hca@linux.ibm.com>
Cc: Vasily Gorbik <gor@linux.ibm.com>
Cc: David S. Miller <davem@davemloft.net>
Cc: Andreas Larsson <andreas@gaisler.com>
Cc: Al Viro <viro@zeniv.linux.org.uk>
Cc: Christian Brauner <brauner@kernel.org>
Cc: Matthew Brost <matthew.brost@intel.com>
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Cc: Rakie Kim <rakie.kim@sk.com>
Cc: Byungchul Park <byungchul@sk.com>
Cc: Gregory Price <gourry@gourry.net>
Cc: Ying Huang <ying.huang@linux.alibaba.com>
Cc: Alistair Popple <apopple@nvidia.com>
Cc: Chris Li <chrisl@kernel.org>
Cc: Kairui Song <kasong@tencent.com>
Cc: Kemeng Shi <shikemeng@huaweicloud.com>
Cc: Nhat Pham <nphamcs@gmail.com>
Cc: Baoquan He <baoquan.he@linux.dev>
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Cc: Chengming Zhou <chengming.zhou@linux.dev>
Cc: Michal Hocko <mhocko@kernel.org>
Cc: Miklos Szeredi <miklos@szeredi.hu>
Cc: Xu Xin <xu.xin@linux.dev>
Cc: Ihor Solodrai <ihor.solodrai@linux.dev>
Cc: Bert Karwatzki <spasswolf@web.de>
---

 drivers/scsi/sg.c |  115 +++++++++++++++++++-------------------------
 1 file changed, 51 insertions(+), 64 deletions(-)

--- a/drivers/scsi/sg.c~scsi-sg-convert-mmap-hook-to-mmap_prepare-and-rework
+++ a/drivers/scsi/sg.c
@@ -1212,85 +1212,72 @@ sg_fasync(int fd, struct file *filp, int
 	return fasync_helper(fd, filp, mode, &sfp->async_qp);
 }
 
-static vm_fault_t
-sg_vma_fault(struct vm_fault *vmf)
+static int sg_discontig_init(void *vm_private_data, void **private)
 {
-	struct vm_area_struct *vma = vmf->vma;
-	Sg_fd *sfp;
-	unsigned long offset, len, sa;
-	Sg_scatter_hold *rsv_schp;
-	int k, length;
-
-	if ((NULL == vma) || (!(sfp = (Sg_fd *) vma->vm_private_data)))
-		return VM_FAULT_SIGBUS;
-	rsv_schp = &sfp->reserve;
-	offset = vmf->pgoff << PAGE_SHIFT;
-	if (offset >= rsv_schp->bufflen)
-		return VM_FAULT_SIGBUS;
-	SCSI_LOG_TIMEOUT(3, sg_printk(KERN_INFO, sfp->parentdp,
-				      "sg_vma_fault: offset=%lu, scatg=%d\n",
-				      offset, rsv_schp->k_use_sg));
-	sa = vma->vm_start;
-	length = 1 << (PAGE_SHIFT + rsv_schp->page_order);
-	for (k = 0; k < rsv_schp->k_use_sg && sa < vma->vm_end; k++) {
-		len = vma->vm_end - sa;
-		len = (len < length) ? len : length;
-		if (offset < len) {
-			struct page *page = rsv_schp->pages[k] + (offset >> PAGE_SHIFT);
-			get_page(page);	/* increment page count */
-			vmf->page = page;
-			return 0; /* success */
-		}
-		sa += len;
-		offset -= len;
+	const unsigned long req_sz = (unsigned long)*private;
+	Sg_fd *sfp = vm_private_data;
+	Sg_scatter_hold *rsv_schp = &sfp->reserve;
+	int err = 0;
+
+	mutex_lock(&sfp->f_mutex);
+	if (req_sz > rsv_schp->bufflen) {
+		err = -ENOMEM;	/* cannot map more than reserved buffer */
+		goto out;
+	}
+	sfp->mmap_called = 1; /* Prevents changes to buffer size. */
+out:
+	mutex_unlock(&sfp->f_mutex);
+	return err;
+}
+
+static int
+sg_discontig_get(struct discontig_kernel_page_state *state)
+{
+	Sg_fd *sfp = state->vm_private_data;
+	Sg_scatter_hold *rsv_schp = &sfp->reserve;
+	const unsigned int order = rsv_schp->page_order;
+	const pgoff_t nr_pages = state->nr_pages_mapped;
+
+	if (nr_pages >= (rsv_schp->bufflen >> PAGE_SHIFT)) {
+		discontig_kernel_map_abort(state);
+		return 0;
 	}
 
-	return VM_FAULT_SIGBUS;
+	SCSI_LOG_TIMEOUT(3, sg_printk(KERN_INFO, sfp->parentdp,
+				      "%s: offset=%lu, scatg=%d\n", __func__,
+				      nr_pages << PAGE_SHIFT, rsv_schp->k_use_sg));
+
+	discontig_kernel_map_page(state, rsv_schp->pages[nr_pages >> order]);
+	return 0;
 }
 
-static const struct vm_operations_struct sg_mmap_vm_ops = {
-	.fault = sg_vma_fault,
+static const struct discontig_kernel_page_ops sg_discontig_ops = {
+	.init = sg_discontig_init,
+	.get = sg_discontig_get,
 };
 
 static int
-sg_mmap(struct file *filp, struct vm_area_struct *vma)
+sg_mmap_prepare(struct vm_area_desc *desc)
 {
-	Sg_fd *sfp;
-	unsigned long req_sz, len, sa;
-	Sg_scatter_hold *rsv_schp;
-	int k, length;
-	int ret = 0;
+	Sg_fd *sfp = desc->file->private_data;
+	const unsigned long req_sz = vma_desc_size(desc);
 
-	if ((!filp) || (!vma) || (!(sfp = (Sg_fd *) filp->private_data)))
+	if (!sfp)
 		return -ENXIO;
-	req_sz = vma->vm_end - vma->vm_start;
+
 	SCSI_LOG_TIMEOUT(3, sg_printk(KERN_INFO, sfp->parentdp,
 				      "sg_mmap starting, vm_start=%p, len=%d\n",
-				      (void *) vma->vm_start, (int) req_sz));
-	if (vma->vm_pgoff)
+				      (void *) desc->start, (int) req_sz));
+
+	if (desc->pgoff)
 		return -EINVAL;	/* want no offset */
-	rsv_schp = &sfp->reserve;
-	mutex_lock(&sfp->f_mutex);
-	if (req_sz > rsv_schp->bufflen) {
-		ret = -ENOMEM;	/* cannot map more than reserved buffer */
-		goto out;
-	}
 
-	sa = vma->vm_start;
-	length = 1 << (PAGE_SHIFT + rsv_schp->page_order);
-	for (k = 0; k < rsv_schp->k_use_sg && sa < vma->vm_end; k++) {
-		len = vma->vm_end - sa;
-		len = (len < length) ? len : length;
-		sa += len;
-	}
+	vma_desc_set_flags(desc, VMA_DONTEXPAND_BIT, VMA_DONTDUMP_BIT);
+	desc->private_data = sfp;
 
-	sfp->mmap_called = 1;
-	vm_flags_set(vma, VM_IO | VM_DONTEXPAND | VM_DONTDUMP);
-	vma->vm_private_data = sfp;
-	vma->vm_ops = &sg_mmap_vm_ops;
-out:
-	mutex_unlock(&sfp->f_mutex);
-	return ret;
+	mmap_action_map_discontig_kernel_pages(desc, (void *)req_sz,
+					       &sg_discontig_ops);
+	return 0;
 }
 
 static void
@@ -1415,7 +1402,7 @@ static const struct file_operations sg_f
 	.unlocked_ioctl = sg_ioctl,
 	.compat_ioctl = compat_ptr_ioctl,
 	.open = sg_open,
-	.mmap = sg_mmap,
+	.mmap_prepare = sg_mmap_prepare,
 	.release = sg_release,
 	.fasync = sg_fasync,
 };
_

Patches currently in -mm which might be from ljs@kernel.org are

mm-vma-fix-expansion-of-vma_mixedmap_bit-vmas.patch
mm-do-not-unintentionally-overwrite-atomic-vma-flags.patch
mm-vma-avoid-losing-atomic-vma-flags-when-setting-sticky-vma-flags.patch