linux-kernel - Re: [RFC PATCH v2 22/69] KVM: x86: Add vm_type to differentiate legacy VMs from protected VMs

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Date:   Tue, 13 Jul 2021 20:39:06 +0000
From:   Sean Christopherson <seanjc@...gle.com>
To:     Paolo Bonzini <pbonzini@...hat.com>
Cc:     isaku.yamahata@...el.com, Thomas Gleixner <tglx@...utronix.de>,
        Ingo Molnar <mingo@...hat.com>, Borislav Petkov <bp@...en8.de>,
        "H . Peter Anvin" <hpa@...or.com>,
        Vitaly Kuznetsov <vkuznets@...hat.com>,
        Wanpeng Li <wanpengli@...cent.com>,
        Jim Mattson <jmattson@...gle.com>,
        Joerg Roedel <joro@...tes.org>, erdemaktas@...gle.com,
        Connor Kuehl <ckuehl@...hat.com>, x86@...nel.org,
        linux-kernel@...r.kernel.org, kvm@...r.kernel.org,
        isaku.yamahata@...il.com,
        Sean Christopherson <sean.j.christopherson@...el.com>,
        Xiaoyao Li <xiaoyao.li@...el.com>
Subject: Re: [RFC PATCH v2 22/69] KVM: x86: Add vm_type to differentiate
 legacy VMs from protected VMs

On Tue, Jul 06, 2021, Paolo Bonzini wrote:
> On 03/07/21 00:04, isaku.yamahata@...el.com wrote:
> >   struct kvm_arch {
> > +	unsigned long vm_type;
> 
> Also why not just int or u8?

Heh, because kvm_dev_ioctl_create_vm() takes an "unsigned long" for the type and
it felt wrong to store it as something else.  Storing it as a smaller field should
be fine, I highly doubt we'll get to 256 types anytime soon :-)

I think kvm_x86_ops.is_vm_type_supported() should take the full size though.