[tip:x86/urgent] x86/entry/64: Update comments and sanity tests for create_gap

[tip-bot for Peter Zijlstra <tipbot@zytor.com>]

Commit-ID:  4234653e882740cbf6625eeee294e388b3176583
Gitweb:     https://git.kernel.org/tip/4234653e882740cbf6625eeee294e388b3176583
Author:     Peter Zijlstra <peterz@infradead.org>
AuthorDate: Thu, 11 Jul 2019 13:40:58 +0200
Committer:  Thomas Gleixner <tglx@linutronix.de>
CommitDate: Wed, 17 Jul 2019 23:17:38 +0200

x86/entry/64: Update comments and sanity tests for create_gap

Commit 2700fefdb2d9 ("x86_64: Add gap to int3 to allow for call
emulation") forgot to update the comment, do so now.

Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Reviewed-by: Steven Rostedt (VMware) <rostedt@goodmis.org>
Acked-by: Andy Lutomirski <luto@kernel.org>
Cc: bp@alien8.de
Cc: torvalds@linux-foundation.org
Cc: hpa@zytor.com
Cc: dave.hansen@linux.intel.com
Cc: jgross@suse.com
Cc: zhe.he@windriver.com
Cc: joel@joelfernandes.org
Cc: devel@etsukata.com
Link: https://lkml.kernel.org/r/20190711114336.059780563@infradead.org

---
 arch/x86/entry/entry_64.S | 17 +++++++++++------
 1 file changed, 11 insertions(+), 6 deletions(-)

diff --git a/arch/x86/entry/entry_64.S b/arch/x86/entry/entry_64.S
index 3db5fede743b..95ae05f0edf2 100644
--- a/arch/x86/entry/entry_64.S
+++ b/arch/x86/entry/entry_64.S
@@ -913,15 +913,16 @@ apicinterrupt IRQ_WORK_VECTOR			irq_work_interrupt		smp_irq_work_interrupt
 /**
  * idtentry - Generate an IDT entry stub
  * @sym:		Name of the generated entry point
- * @do_sym: 		C function to be called
- * @has_error_code: 	True if this IDT vector has an error code on the stack
- * @paranoid: 		non-zero means that this vector may be invoked from
+ * @do_sym:		C function to be called
+ * @has_error_code:	True if this IDT vector has an error code on the stack
+ * @paranoid:		non-zero means that this vector may be invoked from
  *			kernel mode with user GSBASE and/or user CR3.
  *			2 is special -- see below.
  * @shift_ist:		Set to an IST index if entries from kernel mode should
- *             		decrement the IST stack so that nested entries get a
+ *			decrement the IST stack so that nested entries get a
  *			fresh stack.  (This is for #DB, which has a nasty habit
- *             		of recursing.)
+ *			of recursing.)
+ * @create_gap:		create a 6-word stack gap when coming from kernel mode.
  *
  * idtentry generates an IDT stub that sets up a usable kernel context,
  * creates struct pt_regs, and calls @do_sym.  The stub has the following
@@ -951,10 +952,14 @@ ENTRY(\sym)
 	UNWIND_HINT_IRET_REGS offset=\has_error_code*8
 
 	/* Sanity check */
-	.if \shift_ist != -1 && \paranoid == 0
+	.if \shift_ist != -1 && \paranoid != 1
 	.error "using shift_ist requires paranoid=1"
 	.endif
 
+	.if \create_gap && \paranoid
+	.error "using create_gap requires paranoid=0"
+	.endif
+
 	ASM_CLAC
 
 	.if \has_error_code == 0