linux-kernel - [PATCH v3 4/6] x86/entry/64: Update comments and sanity tests for create

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Message-Id: <20190711114336.059780563@infradead.org>
Date:   Thu, 11 Jul 2019 13:40:58 +0200
From:   Peter Zijlstra <peterz@...radead.org>
To:     tglx@...utronix.de, bp@...en8.de, mingo@...nel.org,
        rostedt@...dmis.org, luto@...nel.org, torvalds@...ux-foundation.org
Cc:     hpa@...or.com, dave.hansen@...ux.intel.com, jgross@...e.com,
        linux-kernel@...r.kernel.org, zhe.he@...driver.com,
        joel@...lfernandes.org, devel@...ukata.com, peterz@...radead.org
Subject: [PATCH v3 4/6] 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.

Acked-by: Andy Lutomirski <luto@...nel.org>
Reviewed-by: Steven Rostedt (VMware) <rostedt@...dmis.org>
Signed-off-by: Peter Zijlstra (Intel) <peterz@...radead.org>
---
 arch/x86/entry/entry_64.S |   17 +++++++++++------
 1 file changed, 11 insertions(+), 6 deletions(-)

--- a/arch/x86/entry/entry_64.S
+++ b/arch/x86/entry/entry_64.S
@@ -913,15 +913,16 @@ apicinterrupt IRQ_WORK_VECTOR			irq_work
 /**
  * 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