linux-kernel - [PATCH v2] x86/kvm: Fix broken irq restoration in kvm

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Message-Id: <1615596685-22269-1-git-send-email-wanpengli@tencent.com>
Date:   Sat, 13 Mar 2021 08:51:25 +0800
From:   Wanpeng Li <kernellwp@...il.com>
To:     linux-kernel@...r.kernel.org, kvm@...r.kernel.org
Cc:     Paolo Bonzini <pbonzini@...hat.com>,
        Sean Christopherson <seanjc@...gle.com>,
        Vitaly Kuznetsov <vkuznets@...hat.com>,
        Wanpeng Li <wanpengli@...cent.com>,
        Jim Mattson <jmattson@...gle.com>,
        Joerg Roedel <joro@...tes.org>,
        Mark Rutland <mark.rutland@....com>,
        Thomas Gleixner <tglx@...utronix.de>
Subject: [PATCH v2] x86/kvm: Fix broken irq restoration in kvm_wait

From: Wanpeng Li <wanpengli@...cent.com>

After commit 997acaf6b4b59c (lockdep: report broken irq restoration), the guest 
splatting below during boot:

 raw_local_irq_restore() called with IRQs enabled
 WARNING: CPU: 1 PID: 169 at kernel/locking/irqflag-debug.c:10 warn_bogus_irq_restore+0x26/0x30
 Modules linked in: hid_generic usbhid hid
 CPU: 1 PID: 169 Comm: systemd-udevd Not tainted 5.11.0+ #25
 RIP: 0010:warn_bogus_irq_restore+0x26/0x30
 Call Trace:
  kvm_wait+0x76/0x90
  __pv_queued_spin_lock_slowpath+0x285/0x2e0
  do_raw_spin_lock+0xc9/0xd0
  _raw_spin_lock+0x59/0x70
  lockref_get_not_dead+0xf/0x50
  __legitimize_path+0x31/0x60
  legitimize_root+0x37/0x50
  try_to_unlazy_next+0x7f/0x1d0
  lookup_fast+0xb0/0x170
  path_openat+0x165/0x9b0
  do_filp_open+0x99/0x110
  do_sys_openat2+0x1f1/0x2e0
  do_sys_open+0x5c/0x80
  __x64_sys_open+0x21/0x30
  do_syscall_64+0x32/0x50
  entry_SYSCALL_64_after_hwframe+0x44/0xae

The irqflags handling in kvm_wait() which ends up doing:

	local_irq_save(flags);
	safe_halt();
	local_irq_restore(flags);

which triggered a new consistency checking, we generally expect 
local_irq_save() and local_irq_restore() to be pared and sanely 
nested, and so local_irq_restore() expects to be called with 
irqs disabled. 

This patch fixes it by playing local_irq_disable()/enable() directly.

Cc: Mark Rutland <mark.rutland@....com>
Cc: Thomas Gleixner <tglx@...utronix.de>
Signed-off-by: Wanpeng Li <wanpengli@...cent.com>
---
v1 -> v2:
 * select the alternative fix

 arch/x86/kernel/kvm.c | 10 ++++++----
 1 file changed, 6 insertions(+), 4 deletions(-)

diff --git a/arch/x86/kernel/kvm.c b/arch/x86/kernel/kvm.c
index 5e78e01..7127aef 100644
--- a/arch/x86/kernel/kvm.c
+++ b/arch/x86/kernel/kvm.c
@@ -836,12 +836,13 @@ static void kvm_kick_cpu(int cpu)
 
 static void kvm_wait(u8 *ptr, u8 val)
 {
-	unsigned long flags;
+	bool disabled = irqs_disabled();
 
 	if (in_nmi())
 		return;
 
-	local_irq_save(flags);
+	if (!disabled)
+		local_irq_disable();
 
 	if (READ_ONCE(*ptr) != val)
 		goto out;
@@ -851,13 +852,14 @@ static void kvm_wait(u8 *ptr, u8 val)
 	 * for irq enabled case to avoid hang when lock info is overwritten
 	 * in irq spinlock slowpath and no spurious interrupt occur to save us.
 	 */
-	if (arch_irqs_disabled_flags(flags))
+	if (disabled)
 		halt();
 	else
 		safe_halt();
 
 out:
-	local_irq_restore(flags);
+	if (!disabled)
+		local_irq_enable();
 }
 
 #ifdef CONFIG_X86_32
-- 
2.7.4