[RFC PATCH 1/4 V2] livedump: Add notifier-call-chain intodo_page_fault

[YOSHIDA Masanori]

This patch adds notifier-call-chain that is called in do_page_fault.
Livedump uses this to check if page fault is caused by livedump, and if so,
the fault is handled by livedump's handler function. Otherwise, it is
handled by the original page fault handler.

Signed-off-by: YOSHIDA Masanori <masanori.yoshida.tv@xxxxxxxxxxx>
Cc: Thomas Gleixner <tglx@xxxxxxxxxxxxx>
Cc: Ingo Molnar <mingo@xxxxxxxxxx>
Cc: "H. Peter Anvin" <hpa@xxxxxxxxx>
Cc: x86@xxxxxxxxxx
Cc: Andy Lutomirski <luto@xxxxxxx>
Cc: Kees Cook <keescook@xxxxxxxxxxxx>
Cc: KOSAKI Motohiro <kosaki.motohiro@xxxxxxxxxxxxxx>
Cc: Prarit Bhargava <prarit@xxxxxxxxxx>
Cc: linux-kernel@xxxxxxxxxxxxxxx
---

 arch/x86/include/asm/traps.h |    2 ++
 arch/x86/mm/fault.c          |    7 +++++++
 2 files changed, 9 insertions(+), 0 deletions(-)

diff --git a/arch/x86/include/asm/traps.h b/arch/x86/include/asm/traps.h
index 88eae2a..dcd5318 100644
--- a/arch/x86/include/asm/traps.h
+++ b/arch/x86/include/asm/traps.h
@@ -114,4 +114,6 @@ enum {
 	X86_TRAP_IRET = 32,	/* 32, IRET Exception */
 };
 
+extern struct atomic_notifier_head page_fault_notifier_list;
+
 #endif /* _ASM_X86_TRAPS_H */
diff --git a/arch/x86/mm/fault.c b/arch/x86/mm/fault.c
index 3ecfd1a..f7460e2 100644
--- a/arch/x86/mm/fault.c
+++ b/arch/x86/mm/fault.c
@@ -995,6 +995,8 @@ static int fault_in_kernel_space(unsigned long address)
 	return address >= TASK_SIZE_MAX;
 }
 
+ATOMIC_NOTIFIER_HEAD(page_fault_notifier_list);
+
 /*
  * This routine handles page faults.  It determines the address,
  * and the problem, and then passes it off to one of the appropriate
@@ -1018,6 +1020,11 @@ do_page_fault(struct pt_regs *regs, unsigned long error_code)
 	/* Get the faulting address: */
 	address = read_cr2();
 
+	if (atomic_notifier_call_chain(
+				&page_fault_notifier_list, error_code, regs)
+			== NOTIFY_STOP)
+		return;
+
 	/*
 	 * Detect and handle instructions that would cause a page fault for
 	 * both a tracked kernel page and a userspace page.

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