The patch titled
Subject: dax: check for data cache aliasing at runtime
has been added to the -mm mm-unstable branch. Its filename is
dax-check-for-data-cache-aliasing-at-runtime.patch
This patch will shortly appear at
https://git.kernel.org/pub/scm/linux/kernel/git/akpm/25-new.git/tree/patches/dax-check-for-data-cache-aliasing-at-runtime.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: Mathieu Desnoyers <mathieu.desnoyers@xxxxxxxxxxxx>
Subject: dax: check for data cache aliasing at runtime
Date: Thu, 8 Feb 2024 13:49:07 -0500
Replace the following fs/Kconfig:FS_DAX dependency:
depends on !(ARM || MIPS || SPARC)
By a runtime check within alloc_dax(). This runtime check returns
ERR_PTR(-EOPNOTSUPP) if the @ops parameter is non-NULL (which means the
kernel is using an aliased mapping) on an architecture which has data
cache aliasing.
Change the return value from NULL to PTR_ERR(-EOPNOTSUPP) for CONFIG_DAX=n
for consistency.
This is done in preparation for using cpu_dcache_is_aliasing() in a
following change which will properly support architectures which detect
data cache aliasing at runtime.
Link: https://lkml.kernel.org/r/20240208184913.484340-7-mathieu.desnoyers@xxxxxxxxxxxx
Fixes: d92576f1167c ("dax: does not work correctly with virtual aliasing caches")
Signed-off-by: Mathieu Desnoyers <mathieu.desnoyers@xxxxxxxxxxxx>
Cc: Linus Torvalds <torvalds@xxxxxxxxxxxxxxxxxxxx>
Cc: Dan Williams <dan.j.williams@xxxxxxxxx>
Cc: Vishal Verma <vishal.l.verma@xxxxxxxxx>
Cc: Dave Jiang <dave.jiang@xxxxxxxxx>
Cc: Matthew Wilcox <willy@xxxxxxxxxxxxx>
Cc: Arnd Bergmann <arnd@xxxxxxxx>
Cc: Russell King <linux@xxxxxxxxxxxxxxx>
Cc: Alasdair Kergon <agk@xxxxxxxxxx>
Cc: Dave Chinner <david@xxxxxxxxxxxxx>
Cc: Mike Snitzer <snitzer@xxxxxxxxxx>
Cc: Mikulas Patocka <mpatocka@xxxxxxxxxx>
Signed-off-by: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>
---
drivers/dax/super.c | 15 +++++++++++++++
fs/Kconfig | 1 -
include/linux/dax.h | 6 +-----
3 files changed, 16 insertions(+), 6 deletions(-)
--- a/drivers/dax/super.c~dax-check-for-data-cache-aliasing-at-runtime
+++ a/drivers/dax/super.c
@@ -319,6 +319,11 @@ EXPORT_SYMBOL_GPL(dax_alive);
* that any fault handlers or operations that might have seen
* dax_alive(), have completed. Any operations that start after
* synchronize_srcu() has run will abort upon seeing !dax_alive().
+ *
+ * Note, because alloc_dax() returns an ERR_PTR() on error, callers
+ * typically store its result into a local variable in order to check
+ * the result. Therefore, care must be taken to populate the struct
+ * device dax_dev field make sure the dax_dev is not leaked.
*/
void kill_dax(struct dax_device *dax_dev)
{
@@ -446,6 +451,16 @@ struct dax_device *alloc_dax(void *priva
dev_t devt;
int minor;
+ /*
+ * Unavailable on architectures with virtually aliased data caches,
+ * except for device-dax (NULL operations pointer), which does
+ * not use aliased mappings from the kernel.
+ */
+ if (ops && (IS_ENABLED(CONFIG_ARM) ||
+ IS_ENABLED(CONFIG_MIPS) ||
+ IS_ENABLED(CONFIG_SPARC)))
+ return ERR_PTR(-EOPNOTSUPP);
+
if (WARN_ON_ONCE(ops && !ops->zero_page_range))
return ERR_PTR(-EINVAL);
--- a/fs/Kconfig~dax-check-for-data-cache-aliasing-at-runtime
+++ a/fs/Kconfig
@@ -60,7 +60,6 @@ endif # BLOCK
config FS_DAX
bool "File system based Direct Access (DAX) support"
depends on MMU
- depends on !(ARM || MIPS || SPARC)
depends on ZONE_DEVICE || FS_DAX_LIMITED
select FS_IOMAP
select DAX
--- a/include/linux/dax.h~dax-check-for-data-cache-aliasing-at-runtime
+++ a/include/linux/dax.h
@@ -86,11 +86,7 @@ static inline void *dax_holder(struct da
static inline struct dax_device *alloc_dax(void *private,
const struct dax_operations *ops)
{
- /*
- * Callers should check IS_ENABLED(CONFIG_DAX) to know if this
- * NULL is an error or expected.
- */
- return NULL;
+ return ERR_PTR(-EOPNOTSUPP);
}
static inline void put_dax(struct dax_device *dax_dev)
{
_
Patches currently in -mm which might be from mathieu.desnoyers@xxxxxxxxxxxx are
nvdimm-pmem-fix-leak-on-dax_add_host-failure.patch
nvdimm-pmem-treat-alloc_dax-eopnotsupp-failure-as-non-fatal.patch
dm-treat-alloc_dax-eopnotsupp-failure-as-non-fatal.patch
dcssblk-handle-alloc_dax-eopnotsupp-failure.patch
virtio-treat-alloc_dax-eopnotsupp-failure-as-non-fatal.patch
dax-check-for-data-cache-aliasing-at-runtime.patch
introduce-cpu_dcache_is_aliasing-across-all-architectures.patch
dax-fix-incorrect-list-of-data-cache-aliasing-architectures.patch
nvdimm-pmem-cleanup-alloc_dax-error-handling.patch
dm-cleanup-alloc_dax-error-handling.patch
dcssblk-cleanup-alloc_dax-error-handling.patch
virtio-cleanup-alloc_dax-error-handling.patch
