[PATCH 2/6] uprobes: introduce is_swbp_at_addr_fast()

[Oleg Nesterov <oleg@redhat.com>]

Add the new helper, is_swbp_at_addr_fast(), will be used by
find_active_uprobe().

It is almost the same as is_swbp_at_addr(), but since it plays
with current->mm it can avoid the slow get_user_pages() in the
likely case.
---
 kernel/events/uprobes.c |   23 +++++++++++++++++++++++
 1 files changed, 23 insertions(+), 0 deletions(-)

diff --git a/kernel/events/uprobes.c b/kernel/events/uprobes.c
index 3d0a4d6..2050b1a 100644
--- a/kernel/events/uprobes.c
+++ b/kernel/events/uprobes.c
@@ -1474,6 +1474,29 @@ static bool can_skip_sstep(struct uprobe *uprobe, struct pt_regs *regs)
 	return false;
 }
 
+int __weak is_swbp_at_addr_fast(unsigned long vaddr)
+{
+	uprobe_opcode_t opcode;
+	int fault;
+
+	pagefault_disable();
+	fault = __copy_from_user_inatomic(&opcode, (void __user*)vaddr,
+							sizeof(opcode));
+	pagefault_enable();
+
+	if (unlikely(fault)) {
+		/*
+		 * XXX: read_opcode() lacks FOLL_FORCE, it can fail if
+		 * we race with another thread which does mprotect(NONE)
+		 * after we hit bp.
+		 */
+		if (read_opcode(current->mm, vaddr, &opcode))
+			return -EFAULT;
+	}
+
+	return is_swbp_insn(&opcode);
+}
+
 static struct uprobe *find_active_uprobe(unsigned long bp_vaddr)
 {
 	struct mm_struct *mm = current->mm;
-- 
1.5.5.1


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