linux-kernel - Re: [PATCH] KVM: x86: Initialize tdp

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Message-ID: <20200527162318.GD24461@linux.intel.com>
Date:   Wed, 27 May 2020 09:23:18 -0700
From:   Sean Christopherson <sean.j.christopherson@...el.com>
To:     Paolo Bonzini <pbonzini@...hat.com>
Cc:     Vitaly Kuznetsov <vkuznets@...hat.com>,
        Wanpeng Li <wanpengli@...cent.com>,
        Jim Mattson <jmattson@...gle.com>,
        Joerg Roedel <joro@...tes.org>, kvm@...r.kernel.org,
        linux-kernel@...r.kernel.org,
        syzbot+904752567107eefb728c@...kaller.appspotmail.com
Subject: Re: [PATCH] KVM: x86: Initialize tdp_level during vCPU creation

On Wed, May 27, 2020 at 06:15:27PM +0200, Paolo Bonzini wrote:
> On 27/05/20 12:03, Vitaly Kuznetsov wrote:
> >>  
> >>  	vcpu->arch.maxphyaddr = cpuid_query_maxphyaddr(vcpu);
> >> +	vcpu->arch.tdp_level = kvm_x86_ops.get_tdp_level(vcpu);
> >>  
> >>  	vcpu->arch.pat = MSR_IA32_CR_PAT_DEFAULT;
> > Reviewed-by: Vitaly Kuznetsov <vkuznets@...hat.com>
> > 
> > Looking at kvm_update_cpuid() I was thinking if it would make sense to
> > duplicate the "/* Note, maxphyaddr must be updated before tdp_level. */"
> > comment here (it seems to be a vmx-only thing btw), drop it from
> > kvm_update_cpuid() or move cpuid_query_maxphyaddr() to get_tdp_level()
> > but didn't come to a conclusive answer. 
> 
> Yeah, it makes sense to at least add the comment here too.

Hmm, one option would be to make .get_tdp_level() pure function by passing
in vcpu->arch.maxphyaddr.  That should make the comment redundant.  I don't
love bleeding VMX's implementation into the prototype, but that ship has
kinda already sailed.

Side topic, cpuid_query_maxphyaddr() should be unexported, the RTIT usage can
and should use vcpu->arch.maxphyaddr.  I'll send a patch for that.