On Mon, Jan 13, 2025 at 07:35:07PM -0800, Dan Williams wrote: > Alistair Popple wrote: [...] > ...and here is that aformentioned patch: This patch is different from what you originally posted here: https://yhbt.net/lore/linux-s390/172721874675.497781.3277495908107141898.stgit@xxxxxxxxxxxxxxxxxxxxxxxxx/ > -- 8< -- > Subject: dcssblk: Mark DAX broken, remove FS_DAX_LIMITED support > > From: Dan Williams <dan.j.williams@xxxxxxxxx> > > 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). Specifically it no longer removes PFN_SPECIAL. Was this intentional? Or should I really have picked up the original patch from the mailing list? - Alistair > 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] > Reviewed-by: Gerald Schaefer <gerald.schaefer@xxxxxxxxxxxxx> > Tested-by: Alexander Gordeev <agordeev@xxxxxxxxxxxxx> > Acked-by: David Hildenbrand <david@xxxxxxxxxx> > 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> > Signed-off-by: Dan Williams <dan.j.williams@xxxxxxxxx> > --- > Documentation/filesystems/dax.rst | 1 - > drivers/s390/block/Kconfig | 12 ++++++++++-- > drivers/s390/block/dcssblk.c | 27 +++++++++++++++++---------- > 3 files changed, 27 insertions(+), 13 deletions(-) > > diff --git a/Documentation/filesystems/dax.rst b/Documentation/filesystems/dax.rst > index 719e90f1988e..08dd5e254cc5 100644 > --- a/Documentation/filesystems/dax.rst > +++ b/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 > > > diff --git a/drivers/s390/block/Kconfig b/drivers/s390/block/Kconfig > index e3710a762aba..4bfe469c04aa 100644 > --- a/drivers/s390/block/Kconfig > +++ b/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" > diff --git a/drivers/s390/block/dcssblk.c b/drivers/s390/block/dcssblk.c > index 0f14d279d30b..7248e547fefb 100644 > --- a/drivers/s390/block/dcssblk.c > +++ b/drivers/s390/block/dcssblk.c > @@ -534,6 +534,21 @@ static const struct attribute_group *dcssblk_dev_attr_groups[] = { > 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, struct device_attribute *attr, const char > 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, struct device_attribute *attr, const char > 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_dev_info *dev_info, pgoff_t pgoff, > *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; > }
