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Message-ID: <0100018c40f0fe2d-584bc0df-f14c-49f0-ab82-b918d9e0cc72-000000@email.amazonses.com>
Date: Wed, 6 Dec 2023 21:03:04 +0000
From: John Groves <john@...alactic.com>
To: Dan Williams <dan.j.williams@...el.com>,
John Groves <jgroves@...ron.com>,
John Groves <john@...alactic.com>
Cc: Vishal Verma <vishal.l.verma@...el.com>,
Dave Jiang <dave.jiang@...el.com>,
nvdimm@...ts.linux.dev
<nvdimm@...ts.linux.dev>,
linux-cxl@...r.kernel.org
<linux-cxl@...r.kernel.org>,
linux-kernel@...r.kernel.org
<linux-kernel@...r.kernel.org>,
linux-fsdevel@...r.kernel.org
<linux-fsdevel@...r.kernel.org>,
John Groves <john@...ves.net>
Subject: [PATCH RFC 3/4] dev_dax_iomap: Add dax_operations to /dev/dax struct
dax_device
From: John Groves <john@...ves.net>
This is the primary content of this rfc. Notes about this commit:
* These methods are based somewhat loosely on pmem_dax_ops from
drivers/nvdimm/pmem.c
* dev_dax_direct_access() is physaddr based
* dev_dax_direct_access() works for mmap, but fails dax_copy_to_iter()
on posix read
* dev_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.
I'm hoping somebody (Dan?) can point the way to getting this working
with posix I/O. Does this need to go the memremap route?
Thanks,
John
---
drivers/dax/bus.c | 105 ++++++++++++++++++++++++++++++++++++++++++++++
1 file changed, 105 insertions(+)
diff --git a/drivers/dax/bus.c b/drivers/dax/bus.c
index 1b55fd7aabaf..8f8c2991c7c2 100644
--- a/drivers/dax/bus.c
+++ b/drivers/dax/bus.c
@@ -10,6 +10,12 @@
#include "dax-private.h"
#include "bus.h"
+#if IS_ENABLED(CONFIG_DEV_DAX_IOMAP)
+#include <linux/backing-dev.h>
+#include <linux/pfn_t.h>
+#include <linux/range.h>
+#endif
+
static DEFINE_MUTEX(dax_bus_lock);
#define DAX_NAME_LEN 30
@@ -1374,6 +1380,100 @@ phys_addr_t dax_pgoff_to_phys(struct dev_dax *dev_dax, pgoff_t pgoff,
}
+/* the phys address approach */
+long __dev_dax_direct_access(struct dax_device *dax_dev, pgoff_t pgoff,
+ long nr_pages, enum dax_access_mode mode, void **kaddr,
+ pfn_t *pfn)
+{
+ struct dev_dax *dev_dax = dax_get_private(dax_dev);
+ size_t size = nr_pages << PAGE_SHIFT;
+ size_t offset = pgoff << PAGE_SHIFT;
+ long range_remainder = 0;
+ phys_addr_t phys;
+ int i;
+
+ /*
+ * pmem hides dax ranges by mapping to a contiguous
+ * pmem->virt_addr = devm_mremap_pages() (in pem_attach_disk()).
+ * Is it legal to avoid the vmap overhead (and resource consumption) and just return
+ * a (potentially partial) phys range? This function does this, returning the
+ * phys_addr with the length truncated if necessary to the range remainder
+ */
+ phys = dax_pgoff_to_phys(dev_dax, pgoff, nr_pages << PAGE_SHIFT);
+
+ if (kaddr)
+ *kaddr = (void *)phys;
+
+ if (pfn)
+ *pfn = phys_to_pfn_t(phys, PFN_DEV|PFN_MAP); /* are flags correct? */
+
+ /*
+ * If dax_pgoff_to_phys() also returned the range remainder (range_len - range_offset)
+ * this loop would not be necessary
+ */
+ for (i = 0; i < dev_dax->nr_range; i++) {
+ size_t rlen = range_len(&(dev_dax->ranges[i].range));
+
+ if (offset < rlen) {
+ range_remainder = rlen - offset;
+ break;
+ }
+ offset -= rlen;
+ }
+
+ /*
+ * Return length valid at phys. Hoping callers can deal with len < entire_dax_device
+ * (or < npages). This returns the remaining length in the applicable dax region.
+ */
+ return PHYS_PFN(min_t(size_t, range_remainder, size));
+}
+
+static int dev_dax_zero_page_range(struct dax_device *dax_dev, pgoff_t pgoff,
+ size_t nr_pages)
+{
+ long resid = nr_pages << PAGE_SHIFT;
+ long offset = pgoff << PAGE_SHIFT;
+
+ /* Break into one write per dax region */
+ while (resid > 0) {
+ void *kaddr;
+ pgoff_t poff = offset >> PAGE_SHIFT;
+ long len = __dev_dax_direct_access(dax_dev, poff,
+ nr_pages, DAX_ACCESS, &kaddr, NULL);
+ len = min_t(long, len, PAGE_SIZE);
+ write_dax(kaddr, ZERO_PAGE(0), offset, len);
+
+ offset += len;
+ resid -= len;
+ }
+ return 0;
+}
+
+static long dev_dax_direct_access(struct dax_device *dax_dev,
+ pgoff_t pgoff, long nr_pages, enum dax_access_mode mode,
+ void **kaddr, pfn_t *pfn)
+{
+ return __dev_dax_direct_access(dax_dev, pgoff, nr_pages, mode, kaddr, pfn);
+}
+
+static size_t dev_dax_recovery_write(struct dax_device *dax_dev, pgoff_t pgoff,
+ void *addr, size_t bytes, struct iov_iter *i)
+{
+ size_t len, off;
+
+ off = offset_in_page(addr);
+ len = PFN_PHYS(PFN_UP(off + bytes));
+
+ return _copy_from_iter_flushcache(addr, bytes, i);
+}
+
+static const struct dax_operations dev_dax_ops = {
+ .direct_access = dev_dax_direct_access,
+ .zero_page_range = dev_dax_zero_page_range,
+ .recovery_write = dev_dax_recovery_write,
+};
+#endif /* IS_ENABLED(CONFIG_DEV_DAX_IOMAP) */
+
struct dev_dax *devm_create_dev_dax(struct dev_dax_data *data)
{
struct dax_region *dax_region = data->dax_region;
@@ -1429,11 +1529,16 @@ struct dev_dax *devm_create_dev_dax(struct dev_dax_data *data)
}
}
+#if IS_ENABLED(CONFIG_DEV_DAX_IOMAP)
+ /* holder_ops currently populated separately in a slightly hacky way */
+ dax_dev = alloc_dax(dev_dax, &dev_dax_ops);
+#else
/*
* No dax_operations since there is no access to this device outside of
* mmap of the resulting character device.
*/
dax_dev = alloc_dax(dev_dax, NULL);
+#endif
if (IS_ERR(dax_dev)) {
rc = PTR_ERR(dax_dev);
goto err_alloc_dax;
--
2.40.1
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