linux-kernel - Re: [PATCH 3/6] KVM: x86: Add dedicated emulator helper for grabbing CPUID.maxphyaddr

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Date:   Tue, 3 Mar 2020 11:14:22 +0100
From:   Paolo Bonzini <pbonzini@...hat.com>
To:     Jan Kiszka <jan.kiszka@...mens.com>,
        Sean Christopherson <sean.j.christopherson@...el.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, Xiaoyao Li <xiaoyao.li@...el.com>
Subject: Re: [PATCH 3/6] KVM: x86: Add dedicated emulator helper for grabbing
 CPUID.maxphyaddr

On 03/03/20 10:48, Jan Kiszka wrote:
>>
>> I don't think this is a particularly useful change.  Yes, it's not
>> intuitive but is it more than a matter of documentation (and possibly
>> moving the check_cr_write snippet into a separate function)?
> 
> Besides the non obvious return value of the current function, this
> approach also avoids leaving cpuid traces for querying maxphyaddr, which
> is also not very intuitive IMHO.

There are already other cases where we leave CPUID traces.  We can just
stop tracing if check_limit (which should be renamed to from_guest) is
true; there are other internal cases which call ctxt->ops->get_cpuid,
such as vendor_intel, and those should also use check_limit==true and
check the return value of ctxt->ops->get_cpuid.

Paolo