linux-kernel - Re: [PATCH v2 2/6] x86/kvm: add boot parameter for adding vcpu-id bits

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Date:   Tue, 28 Sep 2021 18:41:28 +0200
From:   Paolo Bonzini <pbonzini@...hat.com>
To:     Juergen Gross <jgross@...e.com>, kvm@...r.kernel.org,
        x86@...nel.org, linux-doc@...r.kernel.org,
        linux-kernel@...r.kernel.org
Cc:     maz@...nel.org, ehabkost@...hat.com,
        Jonathan Corbet <corbet@....net>,
        Sean Christopherson <seanjc@...gle.com>,
        Vitaly Kuznetsov <vkuznets@...hat.com>,
        Wanpeng Li <wanpengli@...cent.com>,
        Jim Mattson <jmattson@...gle.com>,
        Joerg Roedel <joro@...tes.org>,
        Thomas Gleixner <tglx@...utronix.de>,
        Ingo Molnar <mingo@...hat.com>, Borislav Petkov <bp@...en8.de>,
        "H. Peter Anvin" <hpa@...or.com>
Subject: Re: [PATCH v2 2/6] x86/kvm: add boot parameter for adding vcpu-id
 bits

On 03/09/21 15:08, Juergen Gross wrote:
> +	if (vcpu_id_add_bits >= 0) {
> +		n_bits += vcpu_id_add_bits;
> +	} else {
> +		n_bits++;		/* One additional bit for core level. */
> +		if (topology_max_die_per_package() > 1)
> +			n_bits++;	/* One additional bit for die level. */

This needs to be unconditional since it is always possible to emulate a 
multiple-die-per-package topology for a guest, even if the host has just 
one.

Paolo


> +	}
> +
> +	if (!n_bits)