From mboxrd@z Thu Jan 1 00:00:00 1970 From: Wanpeng Li 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: Fri, 4 Aug 2017 09:23:34 +0800 Message-ID: References: <1501554327-3608-1-git-send-email-wanpeng.li@hotmail.com> <20170803134636.GG32403@flask> Mime-Version: 1.0 Content-Type: text/plain; charset="UTF-8" Content-Transfer-Encoding: quoted-printable Cc: "linux-kernel@vger.kernel.org" , kvm , Paolo Bonzini , Wanpeng Li To: =?UTF-8?B?UmFkaW0gS3LEjW3DocWZ?= Return-path: In-Reply-To: <20170803134636.GG32403@flask> Sender: linux-kernel-owner@vger.kernel.org List-Id: kvm.vger.kernel.org 2017-08-03 21:46 GMT+08:00 Radim Kr=C4=8Dm=C3=A1=C5=99 = : > 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, w= hich >> means that tells the kernel to not make use of any IOAPICs that may be p= resent >> in the system. >> >> Actually external_intr variable in nested_vmx_vmexit() is the req_int_wi= n >> variable passed from vcpu_enter_guest() which means that the L0's usersp= ace >> 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 "Acknowled= ge >> 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 Kr=C4=8Dm=C3=A1=C5=99 >> 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 *v= cpu, u32 exit_reason, >> >> vmx_switch_vmcs(vcpu, &vmx->vmcs01); >> >> - if ((exit_reason =3D=3D 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 =3D=3D EXIT_REASON_EXTERNAL_INTERRUPT && >> + kvm_cpu_has_interrupt(vcpu)) { >> int irq =3D kvm_cpu_get_interrupt(vcpu); >> WARN_ON(irq < 0); >> vmcs12->vm_exit_intr_info =3D 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 ex= it" > > 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