x86/entry: Move PUSH_AND_CLEAR_REGS() back into error_entry

commit 2c08b9b38f upstream.

Commit

  ee774dac0d ("x86/entry: Move PUSH_AND_CLEAR_REGS out of error_entry()")

moved PUSH_AND_CLEAR_REGS out of error_entry, into its own function, in
part to avoid calling error_entry() for XenPV.

However, commit

  7c81c0c921 ("x86/entry: Avoid very early RET")

had to change that because the 'ret' was too early and moved it into
idtentry, bloating the text size, since idtentry is expanded for every
exception vector.

However, with the advent of xen_error_entry() in commit

  d147553b64 ("x86/xen: Add UNTRAIN_RET")

it became possible to remove PUSH_AND_CLEAR_REGS from idtentry, back
into *error_entry().

Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Signed-off-by: Borislav Petkov <bp@suse.de>
[cascardo: error_entry still does cld]
Signed-off-by: Thadeu Lima de Souza Cascardo <cascardo@canonical.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

arch/x86/entry/entry_64.S

@@ -320,6 +320,8 @@ SYM_CODE_END(ret_from_fork)
 
 SYM_CODE_START_LOCAL(xen_error_entry)
 	UNWIND_HINT_FUNC
+	PUSH_AND_CLEAR_REGS save_ret=1
+	ENCODE_FRAME_POINTER 8
 	UNTRAIN_RET
 	RET
 SYM_CODE_END(xen_error_entry)
@@ -331,9 +333,6 @@ SYM_CODE_END(xen_error_entry)
  */
 .macro idtentry_body cfunc has_error_code:req
 
-	PUSH_AND_CLEAR_REGS
-	ENCODE_FRAME_POINTER
-
 	/*
 	 * Call error_entry() and switch to the task stack if from userspace.
 	 *
@@ -1014,6 +1013,10 @@ SYM_CODE_END(paranoid_exit)
 SYM_CODE_START_LOCAL(error_entry)
 	UNWIND_HINT_FUNC
 	cld
+
+	PUSH_AND_CLEAR_REGS save_ret=1
+	ENCODE_FRAME_POINTER 8
+
 	testb	$3, CS+8(%rsp)
 	jz	.Lerror_kernelspace