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>

[Clearing of FAULT_FLAG_ALLOW_RETRY is now done in
 handle_speculative_fault()]
[Retry with usual fault path in the case VM_ERROR is returned by
 handle_speculative_fault(). This allows signal to be delivered]
Signed-off-by: Laurent Dufour <redacted>
---
 arch/x86/include/asm/pgtable_types.h |  7 +++++++
 arch/x86/mm/fault.c                  | 19 +++++++++++++++++++
 2 files changed, 26 insertions(+)

diff --git a/arch/x86/include/asm/pgtable_types.h b/arch/x86/include/asm/pgtable_types.h
index bf9638e1ee42..4fd2693a037e 100644
--- a/arch/x86/include/asm/pgtable_types.h
+++ b/arch/x86/include/asm/pgtable_types.h

@@ -234,6 +234,13 @@ enum page_cache_mode {
 #define PGD_IDENT_ATTR	 0x001		/* PRESENT (no other attributes) */
 #endif
 
+/*
+ * Advertise that we call the Speculative Page Fault handler.
+ */
+#ifdef CONFIG_X86_64
+#define __HAVE_ARCH_CALL_SPF
+#endif
+
 #ifdef CONFIG_X86_32
 # include <asm/pgtable_32_types.h>
 #else

diff --git a/arch/x86/mm/fault.c b/arch/x86/mm/fault.c
index 2a1fa10c6a98..4c070b9a4362 100644
--- a/arch/x86/mm/fault.c
+++ b/arch/x86/mm/fault.c

@@ -1365,6 +1365,24 @@ __do_page_fault(struct pt_regs *regs, unsigned long error_code,
 	if (error_code & PF_INSTR)
 		flags |= FAULT_FLAG_INSTRUCTION;
 
+#ifdef __HAVE_ARCH_CALL_SPF
+	if (error_code & PF_USER) {
+		fault = handle_speculative_fault(mm, address, flags);
+
+		/*
+		 * We also check against VM_FAULT_ERROR because we have to
+		 * raise a signal by calling later mm_fault_error() which
+		 * requires the vma pointer to be set. So in that case,
+		 * we fall through the normal path.