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: Wed, 2 Aug 2017 16:05:41 +0800 Message-ID: References: <1501554327-3608-1-git-send-email-wanpeng.li@hotmail.com> <20170801195859.GB1437@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: Sender: linux-kernel-owner@vger.kernel.org List-Id: kvm.vger.kernel.org 2017-08-02 6:42 GMT+08:00 Wanpeng Li : > 2017-08-02 3:59 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_vmexi= t+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_w= in >>> variable passed from vcpu_enter_guest() which means that the L0's users= pace >>> 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 interrup= t which >>> L1 requires to inject to L2, we should not attempt to emualte "Acknowle= dge >>> 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 >>> >>> diff --git 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 =3D=3D EXIT_REASON_EXTERNAL_INTERRUPT) >>> - && nested_exit_intr_ack_set(vcpu)) { >>> + if (nested_exit_intr_ack_set(vcpu) && >>> + exit_reason =3D=3D EXIT_REASON_EXTERNAL_INTERRUPT && >>> + kvm_cpu_has_interrupt(vcpu)) { >> >> This would work as a solution, but I don't think it's the correct >> behavior. >> >> SDM says that with acknowledge interrupt on exit, bit 31 of the VM-exit >> interrupt information (valid interrupt) is always set to 1 on >> EXIT_REASON_EXTERNAL_INTERRUPT. We don't want to break hypervisors >> expecting an interrupt in that case, so we should do a userspace VM exit >> when the window is open and then inject the userspace interrupt with a >> VM exit. > > Agreed. > >> >> The simplest thing that came to my mind is to: >> >> diff --git a/arch/x86/kvm/vmx.c b/arch/x86/kvm/vmx.c >> index 39a6222bf968..9ad0c882c4f5 100644 >> --- a/arch/x86/kvm/vmx.c >> +++ b/arch/x86/kvm/vmx.c >> @@ -10687,7 +10687,8 @@ static int vmx_check_nested_events(struct kvm_vc= pu *vcpu, bool external_intr) >> return 0; >> } >> >> - if ((kvm_cpu_has_interrupt(vcpu) || external_intr) && >> + if ((kvm_cpu_has_interrupt(vcpu) || >> + (external_intr && !nested_exit_intr_ack_set(vcpu))) && >> nested_exit_on_intr(vcpu)) { >> if (vmx->nested.nested_run_pending) >> return -EBUSY; >> > > Agreed. What's your opinion, Paolo? :) Actually I considered the above idea before, it is what SDM defined. Regards, Wanpeng Li > >> but I think it could break more ... actually, why was the window closed? >> >> kvm_vcpu_ready_for_interrupt_injection() checks vmx_interrupt_allowed() >> in order to decide need for the window, but vmx_check_nested_events() >> doesn't care about that at all, so the window might just appear closed. >> Would the following hunk help too? > > In addition, the request window can be requested by L0's userspace > (kvm_arch_pre_run), and the idea below still can't fix in my testing. > > Regards, > Wanpeng Li > >> >> diff --git a/arch/x86/kvm/vmx.c b/arch/x86/kvm/vmx.c >> index 39a6222bf968..7e6caa9c225d 100644 >> --- a/arch/x86/kvm/vmx.c >> +++ b/arch/x86/kvm/vmx.c >> @@ -5567,8 +5567,10 @@ static int vmx_nmi_allowed(struct kvm_vcpu *vcpu) >> >> static int vmx_interrupt_allowed(struct kvm_vcpu *vcpu) >> { >> - return (!to_vmx(vcpu)->nested.nested_run_pending && >> - vmcs_readl(GUEST_RFLAGS) & X86_EFLAGS_IF) && >> + if (is_guest_mode(vcpu)) >> + return !to_vmx(vcpu)->nested.nested_run_pending; >> + >> + return vmcs_readl(GUEST_RFLAGS) & X86_EFLAGS_IF && >> !(vmcs_read32(GUEST_INTERRUPTIBILITY_INFO) & >> (GUEST_INTR_STATE_STI | GUEST_INTR_STATE_MOV_SS)= ); >> } >> >> (It doesn't prevent malicious userspace from hitting the WARN, though.) >> >> Thanks.