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

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Message-ID: <20240506191039.GE13783@ls.amr.corp.intel.com>
Date: Mon, 6 May 2024 12:10:39 -0700
From: Isaku Yamahata <isaku.yamahata@...el.com>
To: Binbin Wu <binbin.wu@...ux.intel.com>
Cc: isaku.yamahata@...el.com, kvm@...r.kernel.org,
	linux-kernel@...r.kernel.org, isaku.yamahata@...il.com,
	Paolo Bonzini <pbonzini@...hat.com>, erdemaktas@...gle.com,
	Sean Christopherson <seanjc@...gle.com>,
	Sagi Shahar <sagis@...gle.com>, Kai Huang <kai.huang@...el.com>,
	chen.bo@...el.com, hang.yuan@...el.com, tina.zhang@...el.com,
	Xiaoyao Li <xiaoyao.li@...el.com>,
	Sean Christopherson <sean.j.christopherson@...el.com>,
	Chao Gao <chao.gao@...el.com>,
	Reinette Chatre <reinette.chatre@...el.com>,
	rick.p.edgecombe@...el.com
Subject: Re: [PATCH v19 088/130] KVM: x86: Add a switch_db_regs flag to
 handle TDX's auto-switched behavior

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