linux-kernel - Re: [PATCH v3] x86/kvm: Fix broken irq restoration in kvm

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Date:   Thu, 18 Mar 2021 18:58:01 +0100
From:   Paolo Bonzini <pbonzini@...hat.com>
To:     Wanpeng Li <kernellwp@...il.com>, linux-kernel@...r.kernel.org,
        kvm@...r.kernel.org
Cc:     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: Re: [PATCH v3] x86/kvm: Fix broken irq restoration in kvm_wait

On 15/03/21 07:55, Wanpeng Li wrote:
> 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>
> ---
> 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