[PATCH] x86-64: relax pvops stub clobber specifications

[Jan Beulich]

Except for the error_exit case, none of the code paths following the
{DIS,EN}ABLE_INTERRUPTS() invocations being modified here make any
assumptions on register values, so all registers can be clobbered
there. In the error_exit case a minor adjustment to register usage
(at once eliminating an instruction) also allows for this to be true.

Signed-off-by: Jan Beulich <jbeulich@xxxxxxxx>
---
 arch/x86/entry/entry_64.S |   15 +++++++--------
 1 file changed, 7 insertions(+), 8 deletions(-)

--- 4.10-rc6/arch/x86/entry/entry_64.S
+++ 4.10-rc6-x86_64-relax-clobbers/arch/x86/entry/entry_64.S
@@ -212,7 +212,7 @@ entry_SYSCALL_64_fastpath:
 	 * If we see that no exit work is required (which we are required
 	 * to check with IRQs off), then we can go straight to SYSRET64.
 	 */
-	DISABLE_INTERRUPTS(CLBR_NONE)
+	DISABLE_INTERRUPTS(CLBR_ANY)
 	TRACE_IRQS_OFF
 	movq	PER_CPU_VAR(current_task), %r11
 	testl	$_TIF_ALLWORK_MASK, TASK_TI_flags(%r11)
@@ -233,7 +233,7 @@ entry_SYSCALL_64_fastpath:
 	 * raise(3) will trigger this, for example.  IRQs are off.
 	 */
 	TRACE_IRQS_ON
-	ENABLE_INTERRUPTS(CLBR_NONE)
+	ENABLE_INTERRUPTS(CLBR_ANY)
 	SAVE_EXTRA_REGS
 	movq	%rsp, %rdi
 	call	syscall_return_slowpath	/* returns with IRQs disabled */
@@ -343,7 +343,7 @@ ENTRY(stub_ptregs_64)
 	 * Called from fast path -- disable IRQs again, pop return address
 	 * and jump to slow path
 	 */
-	DISABLE_INTERRUPTS(CLBR_NONE)
+	DISABLE_INTERRUPTS(CLBR_ANY)
 	TRACE_IRQS_OFF
 	popq	%rax
 	jmp	entry_SYSCALL64_slow_path
@@ -518,7 +518,7 @@ common_interrupt:
 	interrupt do_IRQ
 	/* 0(%rsp): old RSP */
 ret_from_intr:
-	DISABLE_INTERRUPTS(CLBR_NONE)
+	DISABLE_INTERRUPTS(CLBR_ANY)
 	TRACE_IRQS_OFF
 	decl	PER_CPU_VAR(irq_count)
 
@@ -1051,7 +1051,7 @@ END(paranoid_entry)
  * On entry, ebx is "no swapgs" flag (1: don't need swapgs, 0: need it)
  */
 ENTRY(paranoid_exit)
-	DISABLE_INTERRUPTS(CLBR_NONE)
+	DISABLE_INTERRUPTS(CLBR_ANY)
 	TRACE_IRQS_OFF_DEBUG
 	testl	%ebx, %ebx			/* swapgs needed? */
 	jnz	paranoid_exit_no_swapgs
@@ -1156,10 +1156,9 @@ END(error_entry)
  *   0: user gsbase is loaded, we need SWAPGS and standard preparation for return to usermode
  */
 ENTRY(error_exit)
-	movl	%ebx, %eax
-	DISABLE_INTERRUPTS(CLBR_NONE)
+	DISABLE_INTERRUPTS(CLBR_ANY)
 	TRACE_IRQS_OFF
-	testl	%eax, %eax
+	testl	%ebx, %ebx
 	jnz	retint_kernel
 	jmp	retint_user
 END(error_exit)