From 6550c4df7e50d09f86385ce20fd7e969a5638da3 Mon Sep 17 00:00:00 2001 From: Wanpeng Li Date: Mon, 31 Jul 2017 19:25:27 -0700 Subject: [PATCH] KVM: nVMX: Fix interrupt window request with "Acknowledge interrupt on exit" MIME-Version: 1.0 Content-Type: text/plain; charset=utf8 Content-Transfer-Encoding: 8bit ------------[ 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 [Added code comment to make it obvious that the behavior is not correct. We should do a userspace exit with open interrupt window instead of the nested VM exit. This patch still improves the behavior, so it was accepted as a (temporary) workaround.] Signed-off-by: Radim Krčmář --- arch/x86/kvm/vmx.c | 11 +++++++++-- 1 file changed, 9 insertions(+), 2 deletions(-) diff --git a/arch/x86/kvm/vmx.c b/arch/x86/kvm/vmx.c index cbad87e..9b21b12 100644 --- a/arch/x86/kvm/vmx.c +++ b/arch/x86/kvm/vmx.c @@ -11131,8 +11131,15 @@ 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)) { + /* + * TODO: 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, so we shouldn't need + * kvm_cpu_has_interrupt(). See the commit message for details. + */ + 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 | -- 2.7.4