Analysis of the assembly code shows that when using user_mode(regs),
at least the 'andi.' is redone all the time, and also
the 'lwz ,132(r31)' most of the time. With the new form, the 'is_user'
is mapped to cr4, then all further use of is_user results in just
things like 'beq cr4,218 <do_page_fault+0x218>'
Without the patch:
50: 81 1e 00 84 lwz r8,132(r30)
54: 71 09 40 00 andi. r9,r8,16384
58: 40 82 00 0c bne 64 <do_page_fault+0x64>
84: 81 3e 00 84 lwz r9,132(r30)
8c: 71 2a 40 00 andi. r10,r9,16384
90: 41 a2 01 64 beq 1f4 <do_page_fault+0x1f4>
d4: 81 3e 00 84 lwz r9,132(r30)
dc: 71 28 40 00 andi. r8,r9,16384
e0: 41 82 02 08 beq 2e8 <do_page_fault+0x2e8>
108: 81 3e 00 84 lwz r9,132(r30)
110: 71 28 40 00 andi. r8,r9,16384
118: 41 82 02 28 beq 340 <do_page_fault+0x340>
1e4: 81 3e 00 84 lwz r9,132(r30)
1e8: 71 2a 40 00 andi. r10,r9,16384
1ec: 40 82 01 68 bne 354 <do_page_fault+0x354>
228: 81 3e 00 84 lwz r9,132(r30)
22c: 71 28 40 00 andi. r8,r9,16384
230: 41 82 ff c4 beq 1f4 <do_page_fault+0x1f4>
288: 71 2a 40 00 andi. r10,r9,16384
294: 41 a2 fe 60 beq f4 <do_page_fault+0xf4>
50c: 81 3e 00 84 lwz r9,132(r30)
514: 71 2a 40 00 andi. r10,r9,16384
518: 40 a2 fc e0 bne 1f8 <do_page_fault+0x1f8>
534: 81 3e 00 84 lwz r9,132(r30)
53c: 71 2a 40 00 andi. r10,r9,16384
540: 41 82 fc b8 beq 1f8 <do_page_fault+0x1f8>
This patch creates a local var called 'is_user' which contains the
result of user_mode(regs)
With the patch:
20: 81 03 00 84 lwz r8,132(r3)
48: 55 09 97 fe rlwinm r9,r8,18,31,31
58: 2e 09 00 00 cmpwi cr4,r9,0
5c: 40 92 00 0c bne cr4,68 <do_page_fault+0x68>
88: 41 b2 01 90 beq cr4,218 <do_page_fault+0x218>
d4: 40 92 01 d0 bne cr4,2a4 <do_page_fault+0x2a4>
120: 41 b2 00 f8 beq cr4,218 <do_page_fault+0x218>
138: 41 b2 ff a0 beq cr4,d8 <do_page_fault+0xd8>
1d4: 40 92 00 e0 bne cr4,2b4 <do_page_fault+0x2b4>
Signed-off-by: Christophe Leroy <christophe.le...@c-s.fr>
---
arch/powerpc/mm/fault.c | 13 +++++++------
1 file changed, 7 insertions(+), 6 deletions(-)
diff --git a/arch/powerpc/mm/fault.c b/arch/powerpc/mm/fault.c
index b56bf472db6d..8d1639eee3af 100644
--- a/arch/powerpc/mm/fault.c
+++ b/arch/powerpc/mm/fault.c
@@ -202,6 +202,7 @@ int do_page_fault(struct pt_regs *regs, unsigned long
address,
int is_write = 0;
int trap = TRAP(regs);
int is_exec = trap == 0x400;
+ int is_user = user_mode(regs);
int fault;
int rc = 0;
unsigned int inst = 0;
@@ -244,7 +245,7 @@ int do_page_fault(struct pt_regs *regs, unsigned long
address,
* The kernel should never take an execute fault nor should it
* take a page fault to a kernel address.
*/
- if (!user_mode(regs) && (is_exec || (address >= TASK_SIZE))) {
+ if (!is_user && (is_exec || (address >= TASK_SIZE))) {
rc = SIGSEGV;
goto bail;
}
@@ -263,7 +264,7 @@ int do_page_fault(struct pt_regs *regs, unsigned long
address,
local_irq_enable();
if (faulthandler_disabled() || mm == NULL) {
- if (!user_mode(regs)) {
+ if (!is_user) {
rc = SIGSEGV;
goto bail;
}
@@ -284,10 +285,10 @@ int do_page_fault(struct pt_regs *regs, unsigned long
address,
* can result in fault, which will cause a deadlock when called with
* mmap_sem held
*/
- if (is_write && user_mode(regs))
+ if (is_write && is_user)
__get_user(inst, (unsigned int __user *)regs->nip);
- if (user_mode(regs))
+ if (is_user)
flags |= FAULT_FLAG_USER;
/* When running in the kernel we expect faults to occur only to
@@ -306,7 +307,7 @@ int do_page_fault(struct pt_regs *regs, unsigned long
address,
* thus avoiding the deadlock.
*/
if (!down_read_trylock(&mm->mmap_sem)) {
- if (!user_mode(regs) && !search_exception_tables(regs->nip))
+ if (!is_user && !search_exception_tables(regs->nip))
goto bad_area_nosemaphore;
retry:
@@ -506,7 +507,7 @@ int do_page_fault(struct pt_regs *regs, unsigned long
address,
bad_area_nosemaphore:
/* User mode accesses cause a SIGSEGV */
- if (user_mode(regs)) {
+ if (is_user) {
_exception(SIGSEGV, regs, code, address);
goto bail;
}
--
2.12.0
