[RFC PATCH 1/5][RESEND] livedump: Add notifier-call-chain intodo_page_fault

[YOSHIDA Masanori]

This patch adds notifier-call-chain that is called in do_page_fault.
This can be used to check whether page fault occurs for the normal reason,
or it is caused by special write protection, for example Live Dump.

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: Rik van Riel <riel@xxxxxxxxxx>
Cc: Marcelo Tosatti <mtosatti@xxxxxxxxxx>
Cc: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>
Cc: KOSAKI Motohiro <kosaki.motohiro@xxxxxxxxxxxxxx>
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 0012d09..7bf6081 100644
--- a/arch/x86/include/asm/traps.h
+++ b/arch/x86/include/asm/traps.h
@@ -89,4 +89,6 @@ asmlinkage void smp_thermal_interrupt(void);
 asmlinkage void mce_threshold_interrupt(void);
 #endif
 
+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 5db0490..2f8e2a9 100644
--- a/arch/x86/mm/fault.c
+++ b/arch/x86/mm/fault.c
@@ -985,6 +985,8 @@ 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
@@ -1008,6 +1010,11 @@ 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_OK)
+		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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