s390: KVM preparation: provide hook to enable pgstes in user pagetable
The SIE instruction on s390 uses the 2nd half of the page table page to
virtualize the storage keys of a guest. This patch offers the s390_enable_sie
function, which reorganizes the page tables of a single-threaded process to
reserve space in the page table:
s390_enable_sie makes sure that the process is single threaded and then uses
dup_mm to create a new mm with reorganized page tables. The old mm is freed
and the process has now a page status extended field after every page table.
Code that wants to exploit pgstes should SELECT CONFIG_PGSTE.
This patch has a small common code hit, namely making dup_mm non-static.
Edit (Carsten): I've modified Martin's patch, following Jeremy Fitzhardinge's
review feedback. Now we do have the prototype for dup_mm in
include/linux/sched.h. Following Martin's suggestion, s390_enable_sie() does now
call task_lock() to prevent race against ptrace modification of mm_users.
Signed-off-by: Martin Schwidefsky <schwidefsky@de.ibm.com>
Signed-off-by: Carsten Otte <cotte@de.ibm.com>
Acked-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Avi Kivity <avi@qumranet.com>
diff --git a/arch/s390/kernel/setup.c b/arch/s390/kernel/setup.c
index 7141147..2f35133 100644
--- a/arch/s390/kernel/setup.c
+++ b/arch/s390/kernel/setup.c
@@ -316,7 +316,11 @@
early_param("ipldelay", early_parse_ipldelay);
#ifdef CONFIG_S390_SWITCH_AMODE
+#ifdef CONFIG_PGSTE
+unsigned int switch_amode = 1;
+#else
unsigned int switch_amode = 0;
+#endif
EXPORT_SYMBOL_GPL(switch_amode);
static void set_amode_and_uaccess(unsigned long user_amode,