x86/entry: Switch page fault exception to IDTENTRY_RAW

Convert page fault exceptions to IDTENTRY_RAW:

  - Implement the C entry point with DEFINE_IDTENTRY_RAW
  - Add the CR2 read into the exception handler
  - Add the idtentry_enter/exit_cond_rcu() invocations in
    in the regular page fault handler and in the async PF
    part.
  - Emit the ASM stub with DECLARE_IDTENTRY_RAW
  - Remove the ASM idtentry in 64-bit
  - Remove the CR2 read from 64-bit
  - Remove the open coded ASM entry code in 32-bit
  - Fix up the XEN/PV code
  - Remove the old prototypes

No functional change.

Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Signed-off-by: Ingo Molnar <mingo@kernel.org>
Acked-by: Andy Lutomirski <luto@kernel.org>
Link: https://lore.kernel.org/r/20200521202118.238455120@linutronix.de

arch/x86/mm/fault.c

@@ -1357,11 +1357,38 @@ trace_page_fault_entries(struct pt_regs *regs, unsigned long error_code,
 		trace_page_fault_kernel(address, regs, error_code);
 }
 
-dotraplinkage void
-do_page_fault(struct pt_regs *regs, unsigned long hw_error_code,
-		unsigned long address)
+static __always_inline void
+handle_page_fault(struct pt_regs *regs, unsigned long error_code,
+			      unsigned long address)
 {
+	trace_page_fault_entries(regs, error_code, address);
+
+	if (unlikely(kmmio_fault(regs, address)))
+		return;
+
+	/* Was the fault on kernel-controlled part of the address space? */
+	if (unlikely(fault_in_kernel_space(address))) {
+		do_kern_addr_fault(regs, error_code, address);
+	} else {
+		do_user_addr_fault(regs, error_code, address);
+		/*
+		 * User address page fault handling might have reenabled
+		 * interrupts. Fixing up all potential exit points of
+		 * do_user_addr_fault() and its leaf functions is just not
+		 * doable w/o creating an unholy mess or turning the code
+		 * upside down.
+		 */
+		local_irq_disable();
+	}
+}
+
+DEFINE_IDTENTRY_RAW_ERRORCODE(exc_page_fault)
+{
+	unsigned long address = read_cr2();
+	bool rcu_exit;
+
 	prefetchw(&current->mm->mmap_lock);
+
 	/*
 	 * KVM has two types of events that are, logically, interrupts, but
 	 * are unfortunately delivered using the #PF vector.  These events are
@@ -1376,28 +1403,28 @@ do_page_fault(struct pt_regs *regs, unsigned long hw_error_code,
 	 * getting values from real and async page faults mixed up.
 	 *
 	 * Fingers crossed.
+	 *
+	 * The async #PF handling code takes care of idtentry handling
+	 * itself.
 	 */
 	if (kvm_handle_async_pf(regs, (u32)address))
 		return;
 
-	trace_page_fault_entries(regs, hw_error_code, address);
+	/*
+	 * Entry handling for valid #PF from kernel mode is slightly
+	 * different: RCU is already watching and rcu_irq_enter() must not
+	 * be invoked because a kernel fault on a user space address might
+	 * sleep.
+	 *
+	 * In case the fault hit a RCU idle region the conditional entry
+	 * code reenabled RCU to avoid subsequent wreckage which helps
+	 * debugability.
+	 */
+	rcu_exit = idtentry_enter_cond_rcu(regs);
 
-	if (unlikely(kmmio_fault(regs, address)))
-		return;
+	instrumentation_begin();
+	handle_page_fault(regs, error_code, address);
+	instrumentation_end();
 
-	/* Was the fault on kernel-controlled part of the address space? */
-	if (unlikely(fault_in_kernel_space(address))) {
-		do_kern_addr_fault(regs, hw_error_code, address);
-	} else {
-		do_user_addr_fault(regs, hw_error_code, address);
-		/*
-		 * User address page fault handling might have reenabled
-		 * interrupts. Fixing up all potential exit points of
-		 * do_user_addr_fault() and its leaf functions is just not
-		 * doable w/o creating an unholy mess or turning the code
-		 * upside down.
-		 */
-		local_irq_disable();
-	}
+	idtentry_exit_cond_rcu(regs, rcu_exit);
 }
-NOKPROBE_SYMBOL(do_page_fault);