[RFC PATCH v2 7/7] mm,x86: Add speculative pagefault handling

[Laurent Dufour <ldufour@linux.vnet.ibm.com>]

From: Peter Zijlstra <peterz@infradead.org>

Try a speculative fault before acquiring mmap_sem, if it returns with
VM_FAULT_RETRY continue with the mmap_sem acquisition and do the
traditional fault.

Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
---
 arch/x86/mm/fault.c | 18 ++++++++++++++++++
 1 file changed, 18 insertions(+)

diff --git a/arch/x86/mm/fault.c b/arch/x86/mm/fault.c
index dc8023060456..5313ec9ac57e 100644
--- a/arch/x86/mm/fault.c
+++ b/arch/x86/mm/fault.c
@@ -1276,6 +1276,16 @@ __do_page_fault(struct pt_regs *regs, unsigned long error_code,
 	if (error_code & PF_INSTR)
 		flags |= FAULT_FLAG_INSTRUCTION;
 
+	if (error_code & PF_USER) {
+		fault = handle_speculative_fault(mm, address,
+					flags & ~FAULT_FLAG_ALLOW_RETRY);
+
+		if (fault & VM_FAULT_RETRY)
+			goto retry;
+
+		goto done;
+	}
+
 	/*
 	 * When running in the kernel we expect faults to occur only to
 	 * addresses in user space.  All other faults represent errors in
@@ -1379,7 +1389,15 @@ good_area:
 		return;
 	}
 
+	if (unlikely(fault & VM_FAULT_RETRY)) {
+		if (fatal_signal_pending(current))
+			return;
+
+		goto done;
+	}
+
 	up_read(&mm->mmap_sem);
+done:
 	if (unlikely(fault & VM_FAULT_ERROR)) {
 		mm_fault_error(regs, error_code, address, vma, fault);
 		return;
-- 
2.7.4

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