KVM: VMX: Fix invalid guest state detection after task-switch emulation
authorWanpeng Li <wanpeng.li@hotmail.com>
Thu, 20 Jul 2017 08:11:54 +0000 (01:11 -0700)
committerRadim Krčmář <rkrcmar@redhat.com>
Thu, 20 Jul 2017 15:00:00 +0000 (17:00 +0200)
commitf244deed7a254b4a61333e6886575ce0102e8356
treeda8046fc368f57164a8816340465955b5673f3fb
parentc2ce3f5d89d57301e2756ac325fe2ebc33bfec30
KVM: VMX: Fix invalid guest state detection after task-switch emulation

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.

Thanks Radim for moving the update to vmx__set_flags and adding Paolo's
suggestion for the check.

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>
Signed-off-by: Radim Krčmář <rkrcmar@redhat.com>
arch/x86/kvm/vmx.c