mm/secretmem: make it on by default

Following the discussion about direct map fragmentaion at LSF/MM [1], it
appears that direct map fragmentation has a negligible effect on kernel
data accesses.  Since the only reason that warranted secretmem to be
disabled by default was concern about performance regression caused by the
direct map fragmentation, it makes perfect sense to lift this restriction
and make secretmem enabled.

secretmem obeys RLIMIT_MEMBLOCK and as such it is not expected to cause
large fragmentation of the direct map or meaningfull increase in page
tables allocated during split of the large mappings in the direct map.

The secretmem.enable parameter is retained to allow system administrators
to disable secretmem at boot.

Switch the default setting of secretmem.enable parameter to 1.

Link: https://lwn.net/Articles/931406/
Link: https://lkml.kernel.org/r/20230515083400.3563974-1-rppt@kernel.org
Signed-off-by: Mike Rapoport (IBM) <rppt@kernel.org>
Acked-by: David Hildenbrand <david@redhat.com>
Cc: Randy Dunlap <rdunlap@infradead.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>

diff --git a/mm/secretmem.c b/mm/secretmem.c
index 0b502625cd30ed861fa593fbe16cee7207ac720c..974b32ba8b9d4f19e15c080b497c358c3428d98d 100644 (file)
--- a/mm/secretmem.c
+++ b/mm/secretmem.c
@@ -35,7 +35,7 @@
 #define SECRETMEM_MODE_MASK    (0x0)
 #define SECRETMEM_FLAGS_MASK   SECRETMEM_MODE_MASK
 
-static bool secretmem_enable __ro_after_init;
+static bool secretmem_enable __ro_after_init = 1;
 module_param_named(enable, secretmem_enable, bool, 0400);
 MODULE_PARM_DESC(secretmem_enable,
                 "Enable secretmem and memfd_secret(2) system call");