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bh=Lwj5MobrJnNqjEfnyDCKLy+EwAn09sOy0OKym1ak5/U=; b=KbU9kxZBukfYI3wlRAyDVpDz+lTgQ0gTv5Mn8VLwov5BOqx4CYNqymUXFPiTQJMx2S 6U7rB/YCMvQF0unrh+HDBAOWpLBeC6OKVtzFiGrzQf0jCqaO9rEmx7hvqPWmBkdNMzq7 Tb5Nqev8RWd8kAF8a6BYu94IT17w0KYpCyoxsHjwm9nUd6/X3EIM7z1vcS2hKmOWxPdI 7LU3P1iQAxvofmDEMoLB+2SL03Llrck5mbdCcpabKaJZQTTuW8hBo8ty/HhOEo4NJ6mt Nh+vpOAvbB/fCbKifWNzN7GT71dk5cGZkP0lG6A37u5yH7PX8wELV058yDBNGb/cPm3x tyow== X-Gm-Message-State: AOAM532nwqul+Nh/v40O9jQf4ZiUriVn5Wy7Wew6fQsFAtF5bvVSyRl5 5GG728bfqSxN5RpRtC7KUTmEE7ID6A7QIPWWUXmz6mVuIyU= X-Google-Smtp-Source: ABdhPJykN5Bi5N4WPXpFZGHeFc7dsRHkkUyc7QyH+biEyWI1M6bLOwto6RHwjHeIb2PpzXp+z4PQG8QkdMM3ajtVGJY= X-Received: by 2002:a05:6808:10ca:: with SMTP id s10mr15557313ois.33.1614058111252; Mon, 22 Feb 2021 21:28:31 -0800 (PST) MIME-Version: 1.0 References: <1614057902-23774-1-git-send-email-wanpengli@tencent.com> In-Reply-To: <1614057902-23774-1-git-send-email-wanpengli@tencent.com> From: Wanpeng Li Date: Tue, 23 Feb 2021 13:28:19 +0800 Message-ID: Subject: Re: [PATCH] x86/kvm: Fix broken irq restoration in kvm_wait To: LKML , kvm Cc: Paolo Bonzini , Sean Christopherson , Vitaly Kuznetsov , Wanpeng Li , Jim Mattson , Joerg Roedel , Mark Rutland , Thomas Gleixner Content-Type: text/plain; charset="UTF-8" Precedence: bulk List-ID: X-Mailing-List: kvm@vger.kernel.org On Tue, 23 Feb 2021 at 13:25, Wanpeng Li wrote: > > From: Wanpeng Li > > 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 > Cc: Thomas Gleixner > Signed-off-by: Wanpeng Li > --- > 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