linux-kernel - [PATCH 4.4 08/37] kaiser: fix regs to do_nmi() ifndef CONFIG

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Date:   Wed,  3 Jan 2018 21:11:14 +0100
From:   Greg Kroah-Hartman <gregkh@...uxfoundation.org>
To:     linux-kernel@...r.kernel.org
Cc:     Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        stable@...r.kernel.org, Hugh Dickins <hughd@...gle.com>,
        Jiri Kosina <jkosina@...e.cz>
Subject: [PATCH 4.4 08/37] kaiser: fix regs to do_nmi() ifndef CONFIG_KAISER

4.4-stable review patch.  If anyone has any objections, please let me know.

------------------

From: Hugh Dickins <hughd@...gle.com>


pjt has observed that nmi's second (nmi_from_kernel) call to do_nmi()
adjusted the %rdi regs arg, rightly when CONFIG_KAISER, but wrongly
when not CONFIG_KAISER.

Although the minimal change is to add an #ifdef CONFIG_KAISER around
the addq line, that looks cluttered, and I prefer how the first call
to do_nmi() handled it: prepare args in %rdi and %rsi before getting
into the CONFIG_KAISER block, since it does not touch them at all.

And while we're here, place the "#ifdef CONFIG_KAISER" that follows
each, to enclose the "Unconditionally restore CR3" comment: matching
how the "Unconditionally use kernel CR3" comment above is enclosed.

Signed-off-by: Hugh Dickins <hughd@...gle.com>
Acked-by: Jiri Kosina <jkosina@...e.cz>
Signed-off-by: Greg Kroah-Hartman <gregkh@...uxfoundation.org>
---
 arch/x86/entry/entry_64.S |   11 ++++++-----
 1 file changed, 6 insertions(+), 5 deletions(-)

--- a/arch/x86/entry/entry_64.S
+++ b/arch/x86/entry/entry_64.S
@@ -1297,12 +1297,13 @@ ENTRY(nmi)
 	movq	%rax, %cr3
 #endif
 	call	do_nmi
+
+#ifdef CONFIG_KAISER
 	/*
 	 * Unconditionally restore CR3.  I know we return to
 	 * kernel code that needs user CR3, but do we ever return
 	 * to "user mode" where we need the kernel CR3?
 	 */
-#ifdef CONFIG_KAISER
 	popq	%rax
 	mov	%rax, %cr3
 #endif
@@ -1526,6 +1527,8 @@ end_repeat_nmi:
 	SWAPGS
 	xorl	%ebx, %ebx
 1:
+	movq	%rsp, %rdi
+	movq	$-1, %rsi
 #ifdef CONFIG_KAISER
 	/* Unconditionally use kernel CR3 for do_nmi() */
 	/* %rax is saved above, so OK to clobber here */
@@ -1538,16 +1541,14 @@ end_repeat_nmi:
 #endif
 
 	/* paranoidentry do_nmi, 0; without TRACE_IRQS_OFF */
-	movq	%rsp, %rdi
-	addq	$8, %rdi /* point %rdi at ptregs, fixed up for CR3 */
-	movq	$-1, %rsi
 	call	do_nmi
+
+#ifdef CONFIG_KAISER
 	/*
 	 * Unconditionally restore CR3.  We might be returning to
 	 * kernel code that needs user CR3, like just just before
 	 * a sysret.
 	 */
-#ifdef CONFIG_KAISER
 	popq	%rax
 	mov	%rax, %cr3
 #endif