x86/asm/entry/64: Save all regs on interrupt entry

To prepare for the big rewrite of the error and interrupt exit
paths, we will need pt_regs completely filled in.

It's already completely filled in when error_exit runs, so rearrange
interrupt handling to match it.  This will slow down interrupt
handling very slightly (eight instructions), but the
simplification it enables will be more than worth it.

Signed-off-by: Andy Lutomirski <luto@kernel.org>
Cc: Andy Lutomirski <luto@amacapital.net>
Cc: Borislav Petkov <bp@alien8.de>
Cc: Brian Gerst <brgerst@gmail.com>
Cc: Denys Vlasenko <dvlasenk@redhat.com>
Cc: Denys Vlasenko <vda.linux@googlemail.com>
Cc: Frederic Weisbecker <fweisbec@gmail.com>
Cc: H. Peter Anvin <hpa@zytor.com>
Cc: Kees Cook <keescook@chromium.org>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Oleg Nesterov <oleg@redhat.com>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Rik van Riel <riel@redhat.com>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: paulmck@linux.vnet.ibm.com
Link: http://lkml.kernel.org/r/d8a766a7f558b30e6e01352854628a2d9943460c.1435952415.git.luto@kernel.org
Signed-off-by: Ingo Molnar <mingo@kernel.org>

arch/x86/entry/calling.h

@@ -135,9 +135,6 @@ For 32-bit we have the following conventions - kernel is built with
 	movq %rbp, 4*8+\offset(%rsp)
 	movq %rbx, 5*8+\offset(%rsp)
 	.endm
-	.macro SAVE_EXTRA_REGS_RBP offset=0
-	movq %rbp, 4*8+\offset(%rsp)
-	.endm
 
 	.macro RESTORE_EXTRA_REGS offset=0
 	movq 0*8+\offset(%rsp), %r15

arch/x86/entry/entry_64.S

@@ -502,21 +502,13 @@ END(irq_entries_start)
 /* 0(%rsp): ~(interrupt number) */
 	.macro interrupt func
 	cld
-	/*
-	 * Since nothing in interrupt handling code touches r12...r15 members
-	 * of "struct pt_regs", and since interrupts can nest, we can save
-	 * four stack slots and simultaneously provide
-	 * an unwind-friendly stack layout by saving "truncated" pt_regs
-	 * exactly up to rbp slot, without these members.
-	 */
-	ALLOC_PT_GPREGS_ON_STACK -RBP
-	SAVE_C_REGS -RBP
-	/* this goes to 0(%rsp) for unwinder, not for saving the value: */
-	SAVE_EXTRA_REGS_RBP -RBP
+	ALLOC_PT_GPREGS_ON_STACK
+	SAVE_C_REGS
+	SAVE_EXTRA_REGS
 
-	leaq	-RBP(%rsp), %rdi		/* arg1 for \func (pointer to pt_regs) */
+	movq	%rsp,%rdi	/* arg1 for \func (pointer to pt_regs) */
 
-	testb	$3, CS-RBP(%rsp)
+	testb	$3, CS(%rsp)
 	jz	1f
 	SWAPGS
 1:
@@ -553,9 +545,7 @@ ret_from_intr:
 	decl	PER_CPU_VAR(irq_count)
 
 	/* Restore saved previous stack */
-	popq	%rsi
-	/* return code expects complete pt_regs - adjust rsp accordingly: */
-	leaq	-RBP(%rsi), %rsp
+	popq	%rsp
 
 	testb	$3, CS(%rsp)
 	jz	retint_kernel
@@ -580,7 +570,7 @@ retint_swapgs:					/* return to user-space */
 	TRACE_IRQS_IRETQ
 
 	SWAPGS
-	jmp	restore_c_regs_and_iret
+	jmp	restore_regs_and_iret
 
 /* Returning to kernel space */
 retint_kernel:
@@ -604,6 +594,8 @@ retint_kernel:
  * At this label, code paths which return to kernel and to user,
  * which come from interrupts/exception and from syscalls, merge.
  */
+restore_regs_and_iret:
+	RESTORE_EXTRA_REGS
 restore_c_regs_and_iret:
 	RESTORE_C_REGS
 	REMOVE_PT_GPREGS_FROM_STACK 8
@@ -674,12 +666,10 @@ retint_signal:
 	jz	retint_swapgs
 	TRACE_IRQS_ON
 	ENABLE_INTERRUPTS(CLBR_NONE)
-	SAVE_EXTRA_REGS
 	movq	$-1, ORIG_RAX(%rsp)
 	xorl	%esi, %esi			/* oldset */
 	movq	%rsp, %rdi			/* &pt_regs */
 	call	do_notify_resume
-	RESTORE_EXTRA_REGS
 	DISABLE_INTERRUPTS(CLBR_NONE)
 	TRACE_IRQS_OFF
 	GET_THREAD_INFO(%rcx)
@@ -1160,7 +1150,6 @@ END(error_entry)
  */
 ENTRY(error_exit)
 	movl	%ebx, %eax
-	RESTORE_EXTRA_REGS
 	DISABLE_INTERRUPTS(CLBR_NONE)
 	TRACE_IRQS_OFF
 	testl	%eax, %eax