Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1751996AbdHDBXh (ORCPT ); Thu, 3 Aug 2017 21:23:37 -0400 Received: from mail-oi0-f65.google.com ([209.85.218.65]:33000 "EHLO mail-oi0-f65.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751904AbdHDBXf (ORCPT ); Thu, 3 Aug 2017 21:23:35 -0400 MIME-Version: 1.0 In-Reply-To: <20170803134636.GG32403@flask> References: <1501554327-3608-1-git-send-email-wanpeng.li@hotmail.com> <20170803134636.GG32403@flask> From: Wanpeng Li Date: Fri, 4 Aug 2017 09:23:34 +0800 Message-ID: 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 To: =?UTF-8?B?UmFkaW0gS3LEjW3DocWZ?= Cc: "linux-kernel@vger.kernel.org" , kvm , Paolo Bonzini , Wanpeng Li Content-Type: text/plain; charset="UTF-8" Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Transfer-Encoding: 8bit X-MIME-Autoconverted: from quoted-printable to 8bit by nfs id v741NfVq027544 Content-Length: 3424 Lines: 85 2017-08-03 21:46 GMT+08:00 Radim Krčmář : > 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. Thanks Radim. :) In addition, I will think more about it and figure out a finial solution. Regards, Wanpeng Li