2017-07-20 15:57 GMT+08:00 Radim Krčmář <[email protected]>: > 2017-07-19 16:40-0700, Wanpeng Li: >> From: Wanpeng Li <[email protected]> >> >> 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 <[email protected]> >> Cc: Paolo Bonzini <[email protected]> >> Cc: Radim Krčmář <[email protected]> >> Cc: Nadav Amit <[email protected]> >> Signed-off-by: Wanpeng Li <[email protected]> >> --- >> diff --git a/arch/x86/kvm/vmx.c b/arch/x86/kvm/vmx.c >> static void vmx_set_rflags(struct kvm_vcpu *vcpu, unsigned long rflags) >> { >> + unsigned long old_rflags = vmx_get_rflags(vcpu); >> + unsigned long save_rflags = rflags; >> + >> __set_bit(VCPU_EXREG_RFLAGS, (ulong *)&vcpu->arch.regs_avail); >> to_vmx(vcpu)->rflags = rflags; >> if (to_vmx(vcpu)->rmode.vm86_active) { >> @@ -2370,6 +2378,9 @@ static void vmx_set_rflags(struct kvm_vcpu *vcpu, >> unsigned long rflags) >> rflags |= X86_EFLAGS_IOPL | X86_EFLAGS_VM; >> } >> vmcs_writel(GUEST_RFLAGS, rflags); >> + >> + if ((old_rflags ^ save_rflags) & X86_EFLAGS_VM) > > Looks good, thanks to both. > > The desired rflags are saved in to_vmx(vcpu)->rflags, so we don't need > the temporary variable -- would using that or vmx_get_rflags(vcpu) > generate worse code?
Yeah, I will send out a newer version. Regards, Wanpeng Li
