[PATCH v12 28/31] x86/mm: add speculative pagefault handling

[Laurent Dufour]

From: Peter Zijlstra <peterz at 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 at 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]
[Don't build SPF call if !CONFIG_SPECULATIVE_PAGE_FAULT]
[Handle memory protection key fault]
Signed-off-by: Laurent Dufour <ldufour at linux.ibm.com>
---
 arch/x86/mm/fault.c | 14 ++++++++++++++
 1 file changed, 14 insertions(+)

diff --git a/arch/x86/mm/fault.c b/arch/x86/mm/fault.c
index 667f1da36208..4390d207a7a1 100644
--- a/arch/x86/mm/fault.c
+++ b/arch/x86/mm/fault.c
@@ -1401,6 +1401,18 @@ void do_user_addr_fault(struct pt_regs *regs,
 	}
 #endif
 
+	/*
+	 * Do not try to do a speculative page fault if the fault was due to
+	 * protection keys since it can't be resolved.
+	 */
+	if (!(hw_error_code & X86_PF_PK)) {
+		fault = handle_speculative_fault(mm, address, flags);
+		if (fault != VM_FAULT_RETRY) {
+			perf_sw_event(PERF_COUNT_SW_SPF, 1, regs, address);
+			goto done;
+		}
+	}
+
 	/*
 	 * Kernel-mode access to the user address space should only occur
 	 * on well-defined single instructions listed in the exception
@@ -1499,6 +1511,8 @@ void do_user_addr_fault(struct pt_regs *regs,
 	}
 
 	up_read(&mm->mmap_sem);
+
+done:
 	if (unlikely(fault & VM_FAULT_ERROR)) {
 		mm_fault_error(regs, hw_error_code, address, fault);
 		return;
-- 
2.21.0