From mboxrd@z Thu Jan 1 00:00:00 1970 From: Radim =?utf-8?B?S3LEjW3DocWZ?= Subject: Re: [PATCH v2] KVM: nVMX: Fix attempting to emulate "Acknowledge interrupt on exit" when there is no interrupt which L1 requires to inject to L2 Date: Thu, 3 Aug 2017 15:46:36 +0200 Message-ID: <20170803134636.GG32403@flask> References: <1501554327-3608-1-git-send-email-wanpeng.li@hotmail.com> Mime-Version: 1.0 Content-Type: text/plain; charset=utf-8 Content-Transfer-Encoding: 8bit Cc: linux-kernel@vger.kernel.org, kvm@vger.kernel.org, Paolo Bonzini , Wanpeng Li To: Wanpeng Li Return-path: Content-Disposition: inline In-Reply-To: <1501554327-3608-1-git-send-email-wanpeng.li@hotmail.com> Sender: linux-kernel-owner@vger.kernel.org List-Id: kvm.vger.kernel.org 2017-07-31 19:25-0700, Wanpeng Li: > From: Wanpeng Li > > ------------[ cut here ]------------ > WARNING: CPU: 5 PID: 2288 at arch/x86/kvm/vmx.c:11124 nested_vmx_vmexit+0xd64/0xd70 [kvm_intel] > CPU: 5 PID: 2288 Comm: qemu-system-x86 Not tainted 4.13.0-rc2+ #7 > RIP: 0010:nested_vmx_vmexit+0xd64/0xd70 [kvm_intel] > Call Trace: > vmx_check_nested_events+0x131/0x1f0 [kvm_intel] > ? vmx_check_nested_events+0x131/0x1f0 [kvm_intel] > kvm_arch_vcpu_ioctl_run+0x5dd/0x1be0 [kvm] > ? vmx_vcpu_load+0x1be/0x220 [kvm_intel] > ? kvm_arch_vcpu_load+0x62/0x230 [kvm] > kvm_vcpu_ioctl+0x340/0x700 [kvm] > ? kvm_vcpu_ioctl+0x340/0x700 [kvm] > ? __fget+0xfc/0x210 > do_vfs_ioctl+0xa4/0x6a0 > ? __fget+0x11d/0x210 > SyS_ioctl+0x79/0x90 > do_syscall_64+0x8f/0x750 > ? trace_hardirqs_on_thunk+0x1a/0x1c > entry_SYSCALL64_slow_path+0x25/0x25 > > This can be reproduced by booting L1 guest w/ 'noapic' grub parameter, which > means that tells the kernel to not make use of any IOAPICs that may be present > in the system. > > Actually external_intr variable in nested_vmx_vmexit() is the req_int_win > variable passed from vcpu_enter_guest() which means that the L0's userspace > requests an irq window. I observed the scenario (!kvm_cpu_has_interrupt(vcpu) && > L0's userspace reqeusts an irq window) is true, so there is no interrupt which > L1 requires to inject to L2, we should not attempt to emualte "Acknowledge > interrupt on exit" for the irq window requirement in this scenario. > > This patch fixes it by not attempt to emulate "Acknowledge interrupt on exit" > if there is no L1 requirement to inject an interrupt to L2. > > Cc: Paolo Bonzini > Cc: Radim Krčmář > Signed-off-by: Wanpeng Li > --- > v1 -> v2: > * update patch description > * check nested_exit_intr_ack_set() first > > arch/x86/kvm/vmx.c | 5 +++-- > 1 file changed, 3 insertions(+), 2 deletions(-) > > diff --git a/arch/x86/kvm/vmx.c b/arch/x86/kvm/vmx.c > index 2737343..c5a0ab5 100644 > --- a/arch/x86/kvm/vmx.c > +++ b/arch/x86/kvm/vmx.c > @@ -11118,8 +11118,9 @@ static void nested_vmx_vmexit(struct kvm_vcpu *vcpu, u32 exit_reason, > > vmx_switch_vmcs(vcpu, &vmx->vmcs01); > > - if ((exit_reason == EXIT_REASON_EXTERNAL_INTERRUPT) > - && nested_exit_intr_ack_set(vcpu)) { I've added a TODO comment so it's clearer that we should not be here if there is no interrupt. > + if (nested_exit_intr_ack_set(vcpu) && > + exit_reason == EXIT_REASON_EXTERNAL_INTERRUPT && > + kvm_cpu_has_interrupt(vcpu)) { > int irq = kvm_cpu_get_interrupt(vcpu); > WARN_ON(irq < 0); > vmcs12->vm_exit_intr_info = irq | Changed the indentation to the original alignment. Please don't use 1 tab -- the condition and body meld, which makes it harder to read. (2 tabs would be ok too.) And the subject was way too long, so I changed it to KVM: nVMX: Fix interrupt window request with "Acknowledge interrupt on exit" Applied as it results in better behavior, even if it still is incorrect, thanks.