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Message-ID: <20260107153332.64727-5-john@groves.net>
Date: Wed, 7 Jan 2026 09:33:13 -0600
From: John Groves <John@...ves.net>
To: John Groves <John@...ves.net>,
Miklos Szeredi <miklos@...redi.hu>,
Dan Williams <dan.j.williams@...el.com>,
Bernd Schubert <bschubert@....com>,
Alison Schofield <alison.schofield@...el.com>
Cc: John Groves <jgroves@...ron.com>,
Jonathan Corbet <corbet@....net>,
Vishal Verma <vishal.l.verma@...el.com>,
Dave Jiang <dave.jiang@...el.com>,
Matthew Wilcox <willy@...radead.org>,
Jan Kara <jack@...e.cz>,
Alexander Viro <viro@...iv.linux.org.uk>,
David Hildenbrand <david@...nel.org>,
Christian Brauner <brauner@...nel.org>,
"Darrick J . Wong" <djwong@...nel.org>,
Randy Dunlap <rdunlap@...radead.org>,
Jeff Layton <jlayton@...nel.org>,
Amir Goldstein <amir73il@...il.com>,
Jonathan Cameron <Jonathan.Cameron@...wei.com>,
Stefan Hajnoczi <shajnocz@...hat.com>,
Joanne Koong <joannelkoong@...il.com>,
Josef Bacik <josef@...icpanda.com>,
Bagas Sanjaya <bagasdotme@...il.com>,
Chen Linxuan <chenlinxuan@...ontech.com>,
James Morse <james.morse@....com>,
Fuad Tabba <tabba@...gle.com>,
Sean Christopherson <seanjc@...gle.com>,
Shivank Garg <shivankg@....com>,
Ackerley Tng <ackerleytng@...gle.com>,
Gregory Price <gourry@...rry.net>,
Aravind Ramesh <arramesh@...ron.com>,
Ajay Joshi <ajayjoshi@...ron.com>,
venkataravis@...ron.com,
linux-doc@...r.kernel.org,
linux-kernel@...r.kernel.org,
nvdimm@...ts.linux.dev,
linux-cxl@...r.kernel.org,
linux-fsdevel@...r.kernel.org,
John Groves <john@...ves.net>
Subject: [PATCH V3 04/21] dax: Add dax_operations for use by fs-dax on fsdev dax
From: John Groves <John@...ves.net>
* These methods are based on pmem_dax_ops from drivers/nvdimm/pmem.c
* fsdev_dax_direct_access() returns the hpa, pfn and kva. The kva was
newly stored as dev_dax->virt_addr by dev_dax_probe().
* The hpa/pfn are used for mmap (dax_iomap_fault()), and the kva is used
for read/write (dax_iomap_rw())
* fsdev_dax_recovery_write() and dev_dax_zero_page_range() have not been
tested yet. I'm looking for suggestions as to how to test those.
* dax-private.h: add dev_dax->cached_size, which fsdev needs to
remember. The dev_dax size cannot change while a driver is bound
(dev_dax_resize returns -EBUSY if dev->driver is set). Caching the size
at probe time allows fsdev's direct_access path can use it without
acquiring dax_dev_rwsem (which isn't exported anyway).
Signed-off-by: John Groves <john@...ves.net>
---
drivers/dax/dax-private.h | 1 +
drivers/dax/fsdev.c | 80 +++++++++++++++++++++++++++++++++++++++
2 files changed, 81 insertions(+)
diff --git a/drivers/dax/dax-private.h b/drivers/dax/dax-private.h
index 1bb1631af485..fbd8348cc71c 100644
--- a/drivers/dax/dax-private.h
+++ b/drivers/dax/dax-private.h
@@ -85,6 +85,7 @@ struct dev_dax {
struct dax_region *region;
struct dax_device *dax_dev;
void *virt_addr;
+ u64 cached_size;
unsigned int align;
int target_node;
bool dyn_id;
diff --git a/drivers/dax/fsdev.c b/drivers/dax/fsdev.c
index c5c660b193e5..9e2f83aa2584 100644
--- a/drivers/dax/fsdev.c
+++ b/drivers/dax/fsdev.c
@@ -27,6 +27,81 @@
* - No mmap support - all access is through fs-dax/iomap
*/
+static void fsdev_write_dax(void *pmem_addr, struct page *page,
+ unsigned int off, unsigned int len)
+{
+ while (len) {
+ void *mem = kmap_local_page(page);
+ unsigned int chunk = min_t(unsigned int, len, PAGE_SIZE - off);
+
+ memcpy_flushcache(pmem_addr, mem + off, chunk);
+ kunmap_local(mem);
+ len -= chunk;
+ off = 0;
+ page++;
+ pmem_addr += chunk;
+ }
+}
+
+static long __fsdev_dax_direct_access(struct dax_device *dax_dev, pgoff_t pgoff,
+ long nr_pages, enum dax_access_mode mode, void **kaddr,
+ unsigned long *pfn)
+{
+ struct dev_dax *dev_dax = dax_get_private(dax_dev);
+ size_t size = nr_pages << PAGE_SHIFT;
+ size_t offset = pgoff << PAGE_SHIFT;
+ void *virt_addr = dev_dax->virt_addr + offset;
+ phys_addr_t phys;
+ unsigned long local_pfn;
+
+ WARN_ON(!dev_dax->virt_addr);
+
+ phys = dax_pgoff_to_phys(dev_dax, pgoff, nr_pages << PAGE_SHIFT);
+
+ if (kaddr)
+ *kaddr = virt_addr;
+
+ local_pfn = PHYS_PFN(phys);
+ if (pfn)
+ *pfn = local_pfn;
+
+ /*
+ * Use cached_size which was computed at probe time. The size cannot
+ * change while the driver is bound (resize returns -EBUSY).
+ */
+ return PHYS_PFN(min_t(size_t, size, dev_dax->cached_size - offset));
+}
+
+static int fsdev_dax_zero_page_range(struct dax_device *dax_dev,
+ pgoff_t pgoff, size_t nr_pages)
+{
+ void *kaddr;
+
+ WARN_ONCE(nr_pages > 1, "%s: nr_pages > 1\n", __func__);
+ __fsdev_dax_direct_access(dax_dev, pgoff, 1, DAX_ACCESS, &kaddr, NULL);
+ fsdev_write_dax(kaddr, ZERO_PAGE(0), 0, PAGE_SIZE);
+ return 0;
+}
+
+static long fsdev_dax_direct_access(struct dax_device *dax_dev,
+ pgoff_t pgoff, long nr_pages, enum dax_access_mode mode,
+ void **kaddr, unsigned long *pfn)
+{
+ return __fsdev_dax_direct_access(dax_dev, pgoff, nr_pages, mode,
+ kaddr, pfn);
+}
+
+static size_t fsdev_dax_recovery_write(struct dax_device *dax_dev, pgoff_t pgoff,
+ void *addr, size_t bytes, struct iov_iter *i)
+{
+ return _copy_from_iter_flushcache(addr, bytes, i);
+}
+
+static const struct dax_operations dev_dax_ops = {
+ .direct_access = fsdev_dax_direct_access,
+ .zero_page_range = fsdev_dax_zero_page_range,
+ .recovery_write = fsdev_dax_recovery_write,
+};
static void fsdev_cdev_del(void *cdev)
{
@@ -197,6 +272,11 @@ static int fsdev_dax_probe(struct dev_dax *dev_dax)
}
}
+ /* Cache size now; it cannot change while driver is bound */
+ dev_dax->cached_size = 0;
+ for (i = 0; i < dev_dax->nr_range; i++)
+ dev_dax->cached_size += range_len(&dev_dax->ranges[i].range);
+
/*
* FS-DAX compatible mode: Use MEMORY_DEVICE_FS_DAX type and
* do NOT set vmemmap_shift. This leaves folios at order-0,
--
2.49.0
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