The patch titled
Subject: dcssblk: mark DAX broken, remove FS_DAX_LIMITED support
has been added to the -mm mm-unstable branch. Its filename is
dcssblk-mark-dax-broken-remove-fs_dax_limited-support.patch
This patch will shortly appear at
https://git.kernel.org/pub/scm/linux/kernel/git/akpm/25-new.git/tree/patches/dcssblk-mark-dax-broken-remove-fs_dax_limited-support.patch
This patch will later appear in the mm-unstable branch at
git://git.kernel.org/pub/scm/linux/kernel/git/akpm/mm
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------------------------------------------------------
From: Dan Williams <dan.j.williams@xxxxxxxxx>
Subject: dcssblk: mark DAX broken, remove FS_DAX_LIMITED support
Date: Tue, 18 Feb 2025 14:55:34 +1100
The dcssblk driver has long needed special case supoprt to enable limited
dax operation, so called CONFIG_FS_DAX_LIMITED. This mode works around
the incomplete support for ZONE_DEVICE on s390 by forgoing the ability of
dax-mapped pages to support GUP.
Now, pending cleanups to fsdax that fix its reference counting [1] depend
on the ability of all dax drivers to supply ZONE_DEVICE pages.
To allow that work to move forward, dax support needs to be paused for
dcssblk until ZONE_DEVICE support arrives. That work has been known for a
few years [2], and the removal of "pte_devmap" requirements [3] makes the
conversion easier.
For now, place the support behind CONFIG_BROKEN, and remove PFN_SPECIAL
(dcssblk was the only user).
Link: http://lore.kernel.org/cover.9f0e45d52f5cff58807831b6b867084d0b14b61c.1725941415.git-series.apopple@xxxxxxxxxx [1]
Link: http://lore.kernel.org/20210820210318.187742e8@thinkpad/ [2]
Link: http://lore.kernel.org/4511465a4f8429f45e2ac70d2e65dc5e1df1eb47.1725941415.git-series.apopple@xxxxxxxxxx [3]
Link: https://lkml.kernel.org/r/f6a6adc9628745c5545378dcbd64fe68ea8e5ae2.1739850794.git-series.apopple@xxxxxxxxxx
Signed-off-by: Dan Williams <dan.j.williams@xxxxxxxxx>
Reviewed-by: Gerald Schaefer <gerald.schaefer@xxxxxxxxxxxxx>
Tested-by: Alexander Gordeev <agordeev@xxxxxxxxxxxxx>
Acked-by: David Hildenbrand <david@xxxxxxxxxx>
Tested-by: Alison Schofield <alison.schofield@xxxxxxxxx>
Cc: Heiko Carstens <hca@xxxxxxxxxxxxx>
Cc: Vasily Gorbik <gor@xxxxxxxxxxxxx>
Cc: Christian Borntraeger <borntraeger@xxxxxxxxxxxxx>
Cc: Sven Schnelle <svens@xxxxxxxxxxxxx>
Cc: Jan Kara <jack@xxxxxxx>
Cc: Matthew Wilcox <willy@xxxxxxxxxxxxx>
Cc: Christoph Hellwig <hch@xxxxxx>
Cc: Alistair Popple <apopple@xxxxxxxxxx>
Cc: Asahi Lina <lina@xxxxxxxxxxxxx>
Cc: Balbir Singh <balbirs@xxxxxxxxxx>
Cc: Bjorn Helgaas <bhelgaas@xxxxxxxxxx>
Cc: Catalin Marinas <catalin.marinas@xxxxxxx>
Cc: Chunyan Zhang <zhang.lyra@xxxxxxxxx>
Cc: "Darrick J. Wong" <djwong@xxxxxxxxxx>
Cc: Dave Chinner <david@xxxxxxxxxxxxx>
Cc: Dave Hansen <dave.hansen@xxxxxxxxxxxxxxx>
Cc: Dave Jiang <dave.jiang@xxxxxxxxx>
Cc: Huacai Chen <chenhuacai@xxxxxxxxxx>
Cc: Ira Weiny <ira.weiny@xxxxxxxxx>
Cc: Jason Gunthorpe <jgg@xxxxxxxxxx>
Cc: Jason Gunthorpe <jgg@xxxxxxxx>
Cc: John Hubbard <jhubbard@xxxxxxxxxx>
Cc: Logan Gunthorpe <logang@xxxxxxxxxxxx>
Cc: Miaohe Lin <linmiaohe@xxxxxxxxxx>
Cc: Michael Ellerman <mpe@xxxxxxxxxxxxxx>
Cc: Nicholas Piggin <npiggin@xxxxxxxxx>
Cc: Peter Xu <peterx@xxxxxxxxxx>
Cc: Ted Ts'o <tytso@xxxxxxx>
Cc: Vishal Verma <vishal.l.verma@xxxxxxxxx>
Cc: Vivek Goyal <vgoyal@xxxxxxxxxx>
Cc: WANG Xuerui <kernel@xxxxxxxxxx>
Cc: Will Deacon <will@xxxxxxxxxx>
Signed-off-by: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>
---
Documentation/filesystems/dax.rst | 1 -
drivers/s390/block/Kconfig | 12 ++++++++++--
drivers/s390/block/dcssblk.c | 27 +++++++++++++++++----------
3 files changed, 27 insertions(+), 13 deletions(-)
--- a/Documentation/filesystems/dax.rst~dcssblk-mark-dax-broken-remove-fs_dax_limited-support
+++ a/Documentation/filesystems/dax.rst
@@ -207,7 +207,6 @@ implement direct_access.
These block devices may be used for inspiration:
- brd: RAM backed block device driver
-- dcssblk: s390 dcss block device driver
- pmem: NVDIMM persistent memory driver
--- a/drivers/s390/block/dcssblk.c~dcssblk-mark-dax-broken-remove-fs_dax_limited-support
+++ a/drivers/s390/block/dcssblk.c
@@ -534,6 +534,21 @@ static const struct attribute_group *dcs
NULL,
};
+static int dcssblk_setup_dax(struct dcssblk_dev_info *dev_info)
+{
+ struct dax_device *dax_dev;
+
+ if (!IS_ENABLED(CONFIG_DCSSBLK_DAX))
+ return 0;
+
+ dax_dev = alloc_dax(dev_info, &dcssblk_dax_ops);
+ if (IS_ERR(dax_dev))
+ return PTR_ERR(dax_dev);
+ set_dax_synchronous(dax_dev);
+ dev_info->dax_dev = dax_dev;
+ return dax_add_host(dev_info->dax_dev, dev_info->gd);
+}
+
/*
* device attribute for adding devices
*/
@@ -547,7 +562,6 @@ dcssblk_add_store(struct device *dev, st
int rc, i, j, num_of_segments;
struct dcssblk_dev_info *dev_info;
struct segment_info *seg_info, *temp;
- struct dax_device *dax_dev;
char *local_buf;
unsigned long seg_byte_size;
@@ -674,14 +688,7 @@ dcssblk_add_store(struct device *dev, st
if (rc)
goto put_dev;
- dax_dev = alloc_dax(dev_info, &dcssblk_dax_ops);
- if (IS_ERR(dax_dev)) {
- rc = PTR_ERR(dax_dev);
- goto put_dev;
- }
- set_dax_synchronous(dax_dev);
- dev_info->dax_dev = dax_dev;
- rc = dax_add_host(dev_info->dax_dev, dev_info->gd);
+ rc = dcssblk_setup_dax(dev_info);
if (rc)
goto out_dax;
@@ -917,7 +924,7 @@ __dcssblk_direct_access(struct dcssblk_d
*kaddr = __va(dev_info->start + offset);
if (pfn)
*pfn = __pfn_to_pfn_t(PFN_DOWN(dev_info->start + offset),
- PFN_DEV|PFN_SPECIAL);
+ PFN_DEV);
return (dev_sz - offset) / PAGE_SIZE;
}
--- a/drivers/s390/block/Kconfig~dcssblk-mark-dax-broken-remove-fs_dax_limited-support
+++ a/drivers/s390/block/Kconfig
@@ -4,13 +4,21 @@ comment "S/390 block device drivers"
config DCSSBLK
def_tristate m
- select FS_DAX_LIMITED
- select DAX
prompt "DCSSBLK support"
depends on S390 && BLOCK
help
Support for dcss block device
+config DCSSBLK_DAX
+ def_bool y
+ depends on DCSSBLK
+ # requires S390 ZONE_DEVICE support
+ depends on BROKEN
+ select DAX
+ prompt "DCSSBLK DAX support"
+ help
+ Enable DAX operation for the dcss block device
+
config DASD
def_tristate y
prompt "Support for DASD devices"
_
Patches currently in -mm which might be from dan.j.williams@xxxxxxxxx are
dcssblk-mark-dax-broken-remove-fs_dax_limited-support.patch
