Re: [PATCH] KVM: VMX: Fix invalid guest state detection after task-switch emulation

From: Wanpeng Li <kernellwp@gmail.com>
To: "linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>,
	kvm <kvm@vger.kernel.org>
Cc: "Paolo Bonzini" <pbonzini@redhat.com>,
	"Radim Krčmář" <rkrcmar@redhat.com>,
	"Wanpeng Li" <wanpeng.li@hotmail.com>,
	"Nadav Amit" <nadav.amit@gmail.com>
Subject: Re: [PATCH] KVM: VMX: Fix invalid guest state detection after task-switch emulation
Date: Wed, 19 Jul 2017 13:34:23 +0800	[thread overview]
Message-ID: <CANRm+CzO3SKWx2s2F0S9_UfZ-uhY+5jCu+LKRsTKFAUxT2DwTw@mail.gmail.com> (raw)
In-Reply-To: <1499757180-20439-1-git-send-email-wanpeng.li@hotmail.com>

Ping, :)
2017-07-11 15:13 GMT+08:00 Wanpeng Li <kernellwp@gmail.com>:
> From: Wanpeng Li <wanpeng.li@hotmail.com>
>
> This can be reproduced by EPT=1, unrestricted_guest=N, emulate_invalid_state=Y
> or EPT=0, the trace of kvm-unit-tests/taskswitch2.flat is like below, it tries
> to emulate invalid guest state task-switch:
>
> kvm_exit: reason TASK_SWITCH rip 0x0 info 40000058 0
> kvm_emulate_insn: 42000:0:0f 0b (0x2)
> kvm_emulate_insn: 42000:0:0f 0b (0x2) failed
> kvm_inj_exception: #UD (0x0)
> kvm_entry: vcpu 0
> kvm_exit: reason TASK_SWITCH rip 0x0 info 40000058 0
> kvm_emulate_insn: 42000:0:0f 0b (0x2)
> kvm_emulate_insn: 42000:0:0f 0b (0x2) failed
> kvm_inj_exception: #UD (0x0)
> ......................
>
> It appears that the task-switch emulation updates rflags (and vm86
> flag) only after the segments are loaded, causing vmx->emulation_required
> to be set, when in fact invalid guest state emulation is not needed.
>
> This patch fixes it by updating vmx->emulation_required after the
> rflags (and vm86 flag) is updated in task-switch emulation.
>
> Suggested-by: Nadav Amit <nadav.amit@gmail.com>
> Cc: Paolo Bonzini <pbonzini@redhat.com>
> Cc: Radim Krčmář <rkrcmar@redhat.com>
> Cc: Nadav Amit <nadav.amit@gmail.com>
> Signed-off-by: Wanpeng Li <wanpeng.li@hotmail.com>
> ---
>  arch/x86/kvm/vmx.c | 1 +
>  1 file changed, 1 insertion(+)
>
> diff --git a/arch/x86/kvm/vmx.c b/arch/x86/kvm/vmx.c
> index f50cbfd..70270a2 100644
> --- a/arch/x86/kvm/vmx.c
> +++ b/arch/x86/kvm/vmx.c
> @@ -6255,6 +6255,7 @@ static int handle_task_switch(struct kvm_vcpu *vcpu)
>          * TODO: What about debug traps on tss switch?
>          *       Are we supposed to inject them and update dr6?
>          */
> +       vmx->emulation_required = emulation_required(vcpu);
>
>         return 1;
>  }
> --
> 2.7.4
>