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SubjectRe: [PATCH] x86/kvm: Fix broken irq restoration in kvm_wait
On Tue, 23 Feb 2021 at 13:25, Wanpeng Li <kernellwp@gmail.com> 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 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();
> + }

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
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