linux-kernel - Re: [PATCH] KVM: x86/cpuid: Expose the true number of available ASIDs

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Date:   Thu, 15 Jul 2021 19:51:19 +0800
From:   Like Xu <like.xu.linux@...il.com>
To:     Paolo Bonzini <pbonzini@...hat.com>, Joerg Roedel <joro@...tes.org>
Cc:     Sean Christopherson <seanjc@...gle.com>,
        Vitaly Kuznetsov <vkuznets@...hat.com>,
        Wanpeng Li <wanpengli@...cent.com>,
        Jim Mattson <jmattson@...gle.com>, x86@...nel.org,
        linux-kernel@...r.kernel.org, kvm@...r.kernel.org
Subject: Re: [PATCH] KVM: x86/cpuid: Expose the true number of available ASIDs

On 15/7/2021 7:19 pm, Paolo Bonzini wrote:
> On 15/07/21 12:45, Like Xu wrote:
>> The original fixed number "8" was first introduced 11 years ago. Time has
>> passed and now let KVM report the true number of address space 
>> identifiers
>> (ASIDs) that are supported by the processor returned in Fn8000_000A_EBX.
>>
>> It helps user-space to make better decisions about guest values.
>>
>> -        entry->ebx = 8; /* Lets support 8 ASIDs in case we add proper
>> -                   ASID emulation to nested SVM */
> 
> Why, since we don't have ASID emulation yet anyway?
> 
> Paolo

I suppose you're right on the current state.

But do we have an explanation as to why it is hard-coded as 8
and not zero or a real supported number?