linux-kernel - [PATCH v1 5/5] powerpc/fault: Perform exception fixup in do_page

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Message-Id: <5748c8f5cf0a9b3686169e2c7709107e6aaec408.1596734105.git.christophe.leroy@csgroup.eu>
Date:   Thu,  6 Aug 2020 17:15:32 +0000 (UTC)
From:   Christophe Leroy <christophe.leroy@...roup.eu>
To:     Benjamin Herrenschmidt <benh@...nel.crashing.org>,
        Paul Mackerras <paulus@...ba.org>,
        Michael Ellerman <mpe@...erman.id.au>, npiggin@...il.com
Cc:     linux-kernel@...r.kernel.org, linuxppc-dev@...ts.ozlabs.org
Subject: [PATCH v1 5/5] powerpc/fault: Perform exception fixup in
 do_page_fault()

Exception fixup doesn't require the heady full regs saving,
do it from do_page_fault() directly.

For that, split bad_page_fault() in two parts.

As bad_page_fault() can also be called from other places than
handle_page_fault(), it will still perform exception fixup and
fallback on __bad_page_fault().

handle_page_fault() directly calls __bad_page_fault() as the
exception fixup will now be done by do_page_fault()

Signed-off-by: Christophe Leroy <christophe.leroy@...roup.eu>
---
 arch/powerpc/kernel/entry_32.S       |  2 +-
 arch/powerpc/kernel/exceptions-64e.S |  2 +-
 arch/powerpc/kernel/exceptions-64s.S |  2 +-
 arch/powerpc/mm/fault.c              | 33 ++++++++++++++++++++--------
 4 files changed, 27 insertions(+), 12 deletions(-)

diff --git a/arch/powerpc/kernel/entry_32.S b/arch/powerpc/kernel/entry_32.S
index f4d0af8e1136..c198786591f9 100644
--- a/arch/powerpc/kernel/entry_32.S
+++ b/arch/powerpc/kernel/entry_32.S
@@ -678,7 +678,7 @@ handle_page_fault:
 	mr	r5,r3
 	addi	r3,r1,STACK_FRAME_OVERHEAD
 	lwz	r4,_DAR(r1)
-	bl	bad_page_fault
+	bl	__bad_page_fault
 	b	ret_from_except_full
 
 #ifdef CONFIG_PPC_BOOK3S_32
diff --git a/arch/powerpc/kernel/exceptions-64e.S b/arch/powerpc/kernel/exceptions-64e.S
index d9ed79415100..dd9161ea5da8 100644
--- a/arch/powerpc/kernel/exceptions-64e.S
+++ b/arch/powerpc/kernel/exceptions-64e.S
@@ -1024,7 +1024,7 @@ storage_fault_common:
 	mr	r5,r3
 	addi	r3,r1,STACK_FRAME_OVERHEAD
 	ld	r4,_DAR(r1)
-	bl	bad_page_fault
+	bl	__bad_page_fault
 	b	ret_from_except
 
 /*
diff --git a/arch/powerpc/kernel/exceptions-64s.S b/arch/powerpc/kernel/exceptions-64s.S
index f7d748b88705..2cb3bcfb896d 100644
--- a/arch/powerpc/kernel/exceptions-64s.S
+++ b/arch/powerpc/kernel/exceptions-64s.S
@@ -3254,7 +3254,7 @@ handle_page_fault:
 	mr	r5,r3
 	addi	r3,r1,STACK_FRAME_OVERHEAD
 	ld	r4,_DAR(r1)
-	bl	bad_page_fault
+	bl	__bad_page_fault
 	b	interrupt_return
 
 /* We have a data breakpoint exception - handle it */
diff --git a/arch/powerpc/mm/fault.c b/arch/powerpc/mm/fault.c
index edde169ba3a6..bd6e397eb84a 100644
--- a/arch/powerpc/mm/fault.c
+++ b/arch/powerpc/mm/fault.c
@@ -542,10 +542,20 @@ NOKPROBE_SYMBOL(__do_page_fault);
 int do_page_fault(struct pt_regs *regs, unsigned long address,
 		  unsigned long error_code)
 {
+	const struct exception_table_entry *entry;
 	enum ctx_state prev_state = exception_enter();
 	int rc = __do_page_fault(regs, address, error_code);
 	exception_exit(prev_state);
-	return rc;
+	if (likely(!rc))
+		return 0;
+
+	entry = search_exception_tables(regs->nip);
+	if (unlikely(!entry))
+		return rc;
+
+	instruction_pointer_set(regs, extable_fixup(entry));
+
+	return 0;
 }
 NOKPROBE_SYMBOL(do_page_fault);
 
@@ -554,17 +564,10 @@ NOKPROBE_SYMBOL(do_page_fault);
  * It is called from the DSI and ISI handlers in head.S and from some
  * of the procedures in traps.c.
  */
-void bad_page_fault(struct pt_regs *regs, unsigned long address, int sig)
+void __bad_page_fault(struct pt_regs *regs, unsigned long address, int sig)
 {
-	const struct exception_table_entry *entry;
 	int is_write = page_fault_is_write(regs->dsisr);
 
-	/* Are we prepared to handle this fault?  */
-	if ((entry = search_exception_tables(regs->nip)) != NULL) {
-		regs->nip = extable_fixup(entry);
-		return;
-	}
-
 	/* kernel has accessed a bad area */
 
 	switch (TRAP(regs)) {
@@ -598,3 +601,15 @@ void bad_page_fault(struct pt_regs *regs, unsigned long address, int sig)
 
 	die("Kernel access of bad area", regs, sig);
 }
+
+void bad_page_fault(struct pt_regs *regs, unsigned long address, int sig)
+{
+	const struct exception_table_entry *entry;
+
+	/* Are we prepared to handle this fault?  */
+	entry = search_exception_tables(instruction_pointer(regs));
+	if (entry)
+		instruction_pointer_set(regs, extable_fixup(entry));
+	else
+		__bad_page_fault(regs, address, sig);
+}
-- 
2.25.0