Re: [PATCH v19 088/130] KVM: x86: Add a switch_db_regs flag to handle TDX's auto-switched behavior

Isaku Yamahata
2024-05-06T19:10:40Z

On Mon, May 06, 2024 at 11:30:52AM +0800,
Binbin Wu <binbin.wu@linux.intel.com> wrote:

> > diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c
> > index 1b189e86a1f1..fb7597c22f31 100644
> > --- a/arch/x86/kvm/x86.c
> > +++ b/arch/x86/kvm/x86.c
> > @@ -11013,7 +11013,7 @@ static int vcpu_enter_guest(struct kvm_vcpu *vcpu)
> > if (vcpu->arch.guest_fpu.xfd_err)
> > wrmsrl(MSR_IA32_XFD_ERR, vcpu->arch.guest_fpu.xfd_err);
> > - if (unlikely(vcpu->arch.switch_db_regs)) {
> > + if (unlikely(vcpu->arch.switch_db_regs & ~KVM_DEBUGREG_AUTO_SWITCH)) {
>
> As pointed by Paolo in
> https://lore.kernel.org/lkml/ea136ac6-53cf-cdc5-a741-acfb437819b1@redhat.com/
> KVM_DEBUGREG_BP_ENABLED could be set in vcpu->arch.switch_db_regs,  by
> userspace
> kvm_vcpu_ioctl_x86_set_debugregs()  --> kvm_update_dr7()
>
> So it should be fixed as:
>
> -       if (unlikely(vcpu->arch.switch_db_regs)) {
> +       if (unlikely(vcpu->arch.switch_db_regs &&
> +                    !(vcpu->arch.switch_db_regs &
> KVM_DEBUGREG_AUTO_SWITCH))) {

Yes, that's true. Thanks for catching this.
--
Isaku Yamahata <isaku.yamahata@intel.com>