2017-08-02 03:48-0700, Wanpeng Li:
> From: Wanpeng Li <wanpeng.li@xxxxxxxxxxx>
>
> ------------[ 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.
>
> 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.
>
> Cc: Paolo Bonzini <pbonzini@xxxxxxxxxx>
> Cc: Radim Krčmář <rkrcmar@xxxxxxxxxx>
> Signed-off-by: Wanpeng Li <wanpeng.li@xxxxxxxxxxx>
> ---
> v2 -> v3:
> * request an irq window and don't nested vmexit
> v1 -> v2:
> * update patch description
> * check nested_exit_intr_ack_set() first
>
> arch/x86/kvm/vmx.c | 3 ++-
> 1 file changed, 2 insertions(+), 1 deletion(-)
>
> diff --git a/arch/x86/kvm/vmx.c b/arch/x86/kvm/vmx.c
> index 80b20e8..9ef2ec3 100644
> --- a/arch/x86/kvm/vmx.c
> +++ b/arch/x86/kvm/vmx.c
> @@ -10761,7 +10761,8 @@ static int vmx_check_nested_events(struct kvm_vcpu *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))) &&
I think it would be safer to also add something like the second hunk I
posted (that also takes nested_exit_on_intr() into account).
The issue is that we're allowing L2's GUEST_RFLAGS and
GUEST_INTERRUPTIBILITY_INFO to disable userspace interrupt injection
even though neither affect delivery of interrupts into L1.
This means that L2 can block/postpone the delivery to L1 by doing "cli;
busy_loop/normal_critical_section".
Thanks.
> nested_exit_on_intr(vcpu)) {
> if (vmx->nested.nested_run_pending)
> return -EBUSY;
> --
> 2.7.4
>
