On Tue, Feb 23, 2021, Wanpeng Li wrote:
> On Tue, 23 Feb 2021 at 13:25, Wanpeng Li <kernellwp@xxxxxxxxx> wrote:
> >
> > From: Wanpeng Li <wanpengli@xxxxxxxxxxx>
> >
> > 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@xxxxxxx>
> > Cc: Thomas Gleixner <tglx@xxxxxxxxxxxxx>
> > Signed-off-by: Wanpeng Li <wanpengli@xxxxxxxxxxx>
> > ---
> > 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();
> > + }
>
> An alternative fix:
>
> 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
A third option would be to split the paths. In the end, it's only the ptr/val
line that's shared.
---
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 5e78e01ca3b4..78bb0fae3982 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
--
