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?
