x86/entry: Split PUSH_AND_CLEAR_REGS into two submacros

PUSH_AND_CLEAR_REGS, as the name implies, performs two functions:
pushing registers and clearing registers. They don't necessarily have
to be performed in immediate sequence, although all current users
do. Split it into two macros for the case where that isn't desired;
the FRED enabling patchset will eventually make use of this.

Signed-off-by: H. Peter Anvin (Intel) <hpa@zytor.com>
Signed-off-by: Ingo Molnar <mingo@kernel.org>
Link: https://lore.kernel.org/r/20210510185316.3307264-6-hpa@zytor.com

Author: H. Peter Anvin (Intel)

arch/x86/entry/calling.h

@@ -63,7 +63,7 @@ For 32-bit we have the following conventions - kernel is built with
  * for assembly code:
  */
 
-.macro PUSH_AND_CLEAR_REGS rdx=%rdx rax=%rax save_ret=0
+.macro PUSH_REGS rdx=%rdx rax=%rax save_ret=0
 	.if \save_ret
 	pushq	%rsi		/* pt_regs->si */
 	movq	8(%rsp), %rsi	/* temporarily store the return address in %rsi */
@@ -90,7 +90,9 @@ For 32-bit we have the following conventions - kernel is built with
 	.if \save_ret
 	pushq	%rsi		/* return address on top of stack */
 	.endif
+.endm
 
+.macro CLEAR_REGS
 	/*
 	 * Sanitize registers of values that a speculation attack might
 	 * otherwise want to exploit. The lower registers are likely clobbered
@@ -112,6 +114,11 @@ For 32-bit we have the following conventions - kernel is built with
 
 .endm
 
+.macro PUSH_AND_CLEAR_REGS rdx=%rdx rax=%rax save_ret=0
+	PUSH_REGS rdx=\rdx, rax=\rax, save_ret=\save_ret
+	CLEAR_REGS
+.endm
+
 .macro POP_REGS pop_rdi=1 skip_r11rcx=0
 	popq %r15
 	popq %r14