[PATCH] x86/kvm: Fix broken irq restoration in kvm_wait

From: Wanpeng Li <kernellwp@gmail.com>
To: linux-kernel@vger.kernel.org, kvm@vger.kernel.org
Cc: Paolo Bonzini <pbonzini@redhat.com>,
	Sean Christopherson <seanjc@google.com>,
	Vitaly Kuznetsov <vkuznets@redhat.com>,
	Wanpeng Li <wanpengli@tencent.com>,
	Jim Mattson <jmattson@google.com>, Joerg Roedel <joro@8bytes.org>,
	Mark Rutland <mark.rutland@arm.com>,
	Thomas Gleixner <tglx@linutronix.de>
Subject: [PATCH] x86/kvm: Fix broken irq restoration in kvm_wait
Date: Tue, 23 Feb 2021 13:25:02 +0800	[thread overview]
Message-ID: <1614057902-23774-1-git-send-email-wanpengli@tencent.com> (raw)

From: Wanpeng Li <wanpengli@tencent.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 adding a local_irq_disable() after safe_halt() 
to avoid this warning.

Cc: Mark Rutland <mark.rutland@arm.com>
Cc: Thomas Gleixner <tglx@linutronix.de>
Signed-off-by: Wanpeng Li <wanpengli@tencent.com>
---
 arch/x86/kernel/kvm.c | 4 +++-
 1 file changed, 3 insertions(+), 1 deletion(-)

diff --git a/arch/x86/kernel/kvm.c b/arch/x86/kernel/kvm.c
index 5e78e01..688c84a 100644
--- a/arch/x86/kernel/kvm.c
+++ b/arch/x86/kernel/kvm.c
@@ -853,8 +853,10 @@ static void kvm_wait(u8 *ptr, u8 val)
 	 */
 	if (arch_irqs_disabled_flags(flags))
 		halt();
-	else
+	else {
 		safe_halt();
+		local_irq_disable();
+	}
 
 out:
 	local_irq_restore(flags);
-- 
2.7.4

