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:   Thu, 11 Nov 2021 11:28:04 +0800
From:   Xiaoyao Li <xiaoyao.li@...el.com>
To:     Sean Christopherson <seanjc@...gle.com>,
        Paolo Bonzini <pbonzini@...hat.com>
Cc:     "Yamahata, Isaku" <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" <erdemaktas@...gle.com>,
        Connor Kuehl <ckuehl@...hat.com>,
        "x86@...nel.org" <x86@...nel.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        "kvm@...r.kernel.org" <kvm@...r.kernel.org>,
        "isaku.yamahata@...il.com" <isaku.yamahata@...il.com>,
        Sean Christopherson <sean.j.christopherson@...el.com>
Subject: Re: [RFC PATCH v2 22/69] KVM: x86: Add vm_type to differentiate
 legacy VMs from protected VMs

On 7/14/2021 4:39 AM, Sean Christopherson wrote:
> 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 :-)

It's the bit position. We can get only 8 types with u8 actually.

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