linux-kernel - Re: [PATCH v9 4/6] KVM: x86: Introduce untag_addr() in kvm_x86

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Message-ID: <ZJ0rcVpSjbZInnIq@chao-email>
Date:   Thu, 29 Jun 2023 14:57:53 +0800
From:   Chao Gao <chao.gao@...el.com>
To:     Binbin Wu <binbin.wu@...ux.intel.com>
CC:     Sean Christopherson <seanjc@...gle.com>, <kvm@...r.kernel.org>,
        <linux-kernel@...r.kernel.org>, <pbonzini@...hat.com>,
        <kai.huang@...el.com>, <David.Laight@...lab.com>,
        <robert.hu@...ux.intel.com>
Subject: Re: [PATCH v9 4/6] KVM: x86: Introduce untag_addr() in kvm_x86_ops

On Thu, Jun 29, 2023 at 02:12:27PM +0800, Binbin Wu wrote:
>> > +	/*
>> > +	 * Check LAM_U48 in cr3_ctrl_bits to avoid guest_cpuid_has().
>> > +	 * If not set, vCPU doesn't supports LAM.
>> > +	 */
>> > +	if (!(vcpu->arch.cr3_ctrl_bits & X86_CR3_LAM_U48) ||
>> This is unnecessary, KVM should never allow the LAM bits in CR3 to be set if LAM
>> isn't supported.

A corner case is:

If EPT is enabled, CR3 writes are not trapped. then guests can set the
LAM bits in CR3 if hardware supports LAM regardless whether or not guest
enumerates LAM.