+ dax-check-for-data-cache-aliasing-at-runtime.patch added to mm-unstable branch

[Andrew Morton <akpm@linux-foundation.org>]

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@efficios.com>
Subject: dax: check for data cache aliasing at runtime
Date: Mon, 12 Feb 2024 11:30:59 -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/20240212163101.19614-7-mathieu.desnoyers@efficios.com
Fixes: d92576f1167c ("dax: does not work correctly with virtual aliasing caches")
Signed-off-by: Mathieu Desnoyers <mathieu.desnoyers@efficios.com>
Reviewed-by: Dan Williams <dan.j.williams@intel.com>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Dan Williams <dan.j.williams@intel.com>
Cc: Vishal Verma <vishal.l.verma@intel.com>
Cc: Dave Jiang <dave.jiang@intel.com>
Cc: Matthew Wilcox <willy@infradead.org>
Cc: Arnd Bergmann <arnd@arndb.de>
Cc: Russell King <linux@armlinux.org.uk>
Cc: Alasdair Kergon <agk@redhat.com>
Cc: Dave Chinner <david@fromorbit.com>
Cc: Michael Sclafani <dm-devel@lists.linux.dev>
Cc: Mike Snitzer <snitzer@kernel.org>
Cc: Mikulas Patocka <mpatocka@redhat.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
---

 drivers/dax/super.c |   10 ++++++++++
 fs/Kconfig          |    1 -
 2 files changed, 10 insertions(+), 1 deletion(-)

--- a/drivers/dax/super.c~dax-check-for-data-cache-aliasing-at-runtime
+++ a/drivers/dax/super.c
@@ -451,6 +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
_

Patches currently in -mm which might be from mathieu.desnoyers@efficios.com are

nvdimm-pmem-fix-leak-on-dax_add_host-failure.patch
dax-alloc_dax-return-err_ptr-eopnotsupp-for-config_dax=n.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