[PATCH v3] x86/kvm: Fix broken irq restoration in kvm_wait

[PATCH v3] x86/kvm: Fix broken irq restoration in kvm_wait

[Wanpeng Li]

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 playing local_irq_disable()/enable() directly.

Cc: Mark Rutland <mark.rutland@arm.com>
Cc: Thomas Gleixner <tglx@linutronix.de>
Signed-off-by: Wanpeng Li <wanpengli@tencent.com>
---
v2 -> v3:
 * per Sean's suggestion

 arch/x86/kernel/kvm.c | 23 ++++++++++-------------
 1 file changed, 10 insertions(+), 13 deletions(-)

diff --git a/arch/x86/kernel/kvm.c b/arch/x86/kernel/kvm.c
index 5e78e01..72dbb74 100644
--- a/arch/x86/kernel/kvm.c
+++ b/arch/x86/kernel/kvm.c
@@ -836,28 +836,25 @@ static void kvm_kick_cpu(int cpu)
 
 static void kvm_wait(u8 *ptr, u8 val)
 {
-	unsigned long flags;
-
 	if (in_nmi())
 		return;
 
-	local_irq_save(flags);
-
-	if (READ_ONCE(*ptr) != val)
-		goto out;
-
 	/*
 	 * halt until it's our turn and kicked. Note that we do safe halt
 	 * 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))
-		halt();
-	else
-		safe_halt();
+	if (irqs_disabled()) {
+		if (READ_ONCE(*ptr) == val)
+			halt();
+	} else {
+		local_irq_disable();
 
-out:
-	local_irq_restore(flags);
+		if (READ_ONCE(*ptr) == val)
+			safe_halt();
+
+		local_irq_enable();
+	}
 }
 
 #ifdef CONFIG_X86_32
-- 
2.7.4

Re: [PATCH v3] x86/kvm: Fix broken irq restoration in kvm_wait

[Paolo Bonzini]

On 15/03/21 07:55, Wanpeng Li wrote:
> 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 playing local_irq_disable()/enable() directly.
> 
> Cc: Mark Rutland <mark.rutland@arm.com>
> Cc: Thomas Gleixner <tglx@linutronix.de>
> Signed-off-by: Wanpeng Li <wanpengli@tencent.com>
> ---
> v2 -> v3:
>   * per Sean's suggestion
> 
>   arch/x86/kernel/kvm.c | 23 ++++++++++-------------
>   1 file changed, 10 insertions(+), 13 deletions(-)
> 
> diff --git a/arch/x86/kernel/kvm.c b/arch/x86/kernel/kvm.c
> index 5e78e01..72dbb74 100644
> --- a/arch/x86/kernel/kvm.c
> +++ b/arch/x86/kernel/kvm.c
> @@ -836,28 +836,25 @@ static void kvm_kick_cpu(int cpu)
>   
>   static void kvm_wait(u8 *ptr, u8 val)
>   {
> -	unsigned long flags;
> -
>   	if (in_nmi())
>   		return;
>   
> -	local_irq_save(flags);
> -
> -	if (READ_ONCE(*ptr) != val)
> -		goto out;
> -
>   	/*
>   	 * halt until it's our turn and kicked. Note that we do safe halt
>   	 * 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))
> -		halt();
> -	else
> -		safe_halt();
> +	if (irqs_disabled()) {
> +		if (READ_ONCE(*ptr) == val)
> +			halt();
> +	} else {
> +		local_irq_disable();
>   
> -out:
> -	local_irq_restore(flags);
> +		if (READ_ONCE(*ptr) == val)
> +			safe_halt();
> +
> +		local_irq_enable();
> +	}
>   }
>   
>   #ifdef CONFIG_X86_32
> 

Queued, thanks.

Paolo