linux-kernel - [tip:x86/urgent] x86/entry/64: Fix entry_SYSCALL_64_after

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Message-ID: <tip-548c3050ea8d16997ae27f9e080a8338a606fc93@git.kernel.org>
Date:   Tue, 21 Nov 2017 23:45:53 -0800
From:   tip-bot for Andy Lutomirski <tipbot@...or.com>
To:     linux-tip-commits@...r.kernel.org
Cc:     hpa@...or.com, torvalds@...ux-foundation.org, tglx@...utronix.de,
        mingo@...nel.org, linux-kernel@...r.kernel.org,
        peterz@...radead.org, bpetkov@...e.de, dave.hansen@...el.com,
        luto@...nel.org, jpoimboe@...hat.com, jgross@...e.com,
        brgerst@...il.com, boris.ostrovsky@...cle.com
Subject: [tip:x86/urgent] x86/entry/64: Fix entry_SYSCALL_64_after_hwframe()
 IRQ tracing

Commit-ID:  548c3050ea8d16997ae27f9e080a8338a606fc93
Gitweb:     https://git.kernel.org/tip/548c3050ea8d16997ae27f9e080a8338a606fc93
Author:     Andy Lutomirski <luto@...nel.org>
AuthorDate: Tue, 21 Nov 2017 20:43:56 -0800
Committer:  Ingo Molnar <mingo@...nel.org>
CommitDate: Wed, 22 Nov 2017 06:35:48 +0100

x86/entry/64: Fix entry_SYSCALL_64_after_hwframe() IRQ tracing

When I added entry_SYSCALL_64_after_hwframe(), I left TRACE_IRQS_OFF
before it.  This means that users of entry_SYSCALL_64_after_hwframe()
were responsible for invoking TRACE_IRQS_OFF, and the one and only
user (Xen, added in the same commit) got it wrong.

I think this would manifest as a warning if a Xen PV guest with
CONFIG_DEBUG_LOCKDEP=y were used with context tracking.  (The
context tracking bit is to cause lockdep to get invoked before we
turn IRQs back on.)  I haven't tested that for real yet because I
can't get a kernel configured like that to boot at all on Xen PV.

Move TRACE_IRQS_OFF below the label.

Signed-off-by: Andy Lutomirski <luto@...nel.org>
Cc: Boris Ostrovsky <boris.ostrovsky@...cle.com>
Cc: Borislav Petkov <bpetkov@...e.de>
Cc: Brian Gerst <brgerst@...il.com>
Cc: Dave Hansen <dave.hansen@...el.com>
Cc: Josh Poimboeuf <jpoimboe@...hat.com>
Cc: Juergen Gross <jgross@...e.com>
Cc: Linus Torvalds <torvalds@...ux-foundation.org>
Cc: Peter Zijlstra <peterz@...radead.org>
Cc: Thomas Gleixner <tglx@...utronix.de>
Cc: stable@...r.kernel.org
Fixes: 8a9949bc71a7 ("x86/xen/64: Rearrange the SYSCALL entries")
Link: http://lkml.kernel.org/r/9150aac013b7b95d62c2336751d5b6e91d2722aa.1511325444.git.luto@kernel.org
Signed-off-by: Ingo Molnar <mingo@...nel.org>
---
 arch/x86/entry/entry_64.S | 4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)

diff --git a/arch/x86/entry/entry_64.S b/arch/x86/entry/entry_64.S
index a2b30ec..5063ed1 100644
--- a/arch/x86/entry/entry_64.S
+++ b/arch/x86/entry/entry_64.S
@@ -148,8 +148,6 @@ ENTRY(entry_SYSCALL_64)
 	movq	%rsp, PER_CPU_VAR(rsp_scratch)
 	movq	PER_CPU_VAR(cpu_current_top_of_stack), %rsp
 
-	TRACE_IRQS_OFF
-
 	/* Construct struct pt_regs on stack */
 	pushq	$__USER_DS			/* pt_regs->ss */
 	pushq	PER_CPU_VAR(rsp_scratch)	/* pt_regs->sp */
@@ -170,6 +168,8 @@ GLOBAL(entry_SYSCALL_64_after_hwframe)
 	sub	$(6*8), %rsp			/* pt_regs->bp, bx, r12-15 not saved */
 	UNWIND_HINT_REGS extra=0
 
+	TRACE_IRQS_OFF
+
 	/*
 	 * If we need to do entry work or if we guess we'll need to do
 	 * exit work, go straight to the slow path.