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([2001:b07:6468:f312:c8dd:75d4:99ab:290a]) by smtp.gmail.com with ESMTPSA id e8sm2962600wme.14.2021.03.18.10.58.03 (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Thu, 18 Mar 2021 10:58:03 -0700 (PDT) Subject: Re: [PATCH v3] x86/kvm: Fix broken irq restoration in kvm_wait To: Wanpeng Li , linux-kernel@vger.kernel.org, kvm@vger.kernel.org Cc: Sean Christopherson , Vitaly Kuznetsov , Wanpeng Li , Jim Mattson , Joerg Roedel , Mark Rutland , Thomas Gleixner References: <1615791328-2735-1-git-send-email-wanpengli@tencent.com> From: Paolo Bonzini Message-ID: Date: Thu, 18 Mar 2021 18:58:01 +0100 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:78.0) Gecko/20100101 Thunderbird/78.7.0 MIME-Version: 1.0 In-Reply-To: <1615791328-2735-1-git-send-email-wanpengli@tencent.com> Content-Type: text/plain; charset=utf-8; format=flowed Content-Language: en-US Content-Transfer-Encoding: 7bit Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On 15/03/21 07:55, 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 playing local_irq_disable()/enable() directly. > > Cc: Mark Rutland > Cc: Thomas Gleixner > Signed-off-by: Wanpeng Li > --- > 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