linux-kernel - Re: [RFC PATCH 1/4] KVM: selftests: Add support for creating non-default type VMs

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Message-ID: <YQsjQ5aJokV1HZ8N@google.com>
Date:   Wed, 4 Aug 2021 23:31:15 +0000
From:   Sean Christopherson <seanjc@...gle.com>
To:     Erdem Aktas <erdemaktas@...gle.com>
Cc:     Maxim Levitsky <mlevitsk@...hat.com>,
        Xiaoyao Li <xiaoyao.li@...el.com>,
        linux-kselftest@...r.kernel.org, Peter Gonda <pgonda@...gle.com>,
        Marc Orr <marcorr@...gle.com>, Sagi Shahar <sagis@...gle.com>,
        Paolo Bonzini <pbonzini@...hat.com>,
        Shuah Khan <shuah@...nel.org>,
        Andrew Jones <drjones@...hat.com>,
        Ben Gardon <bgardon@...gle.com>, Peter Xu <peterx@...hat.com>,
        David Matlack <dmatlack@...gle.com>,
        Emanuele Giuseppe Esposito <eesposit@...hat.com>,
        Christian Borntraeger <borntraeger@...ibm.com>,
        Ricardo Koller <ricarkol@...gle.com>,
        Eric Auger <eric.auger@...hat.com>,
        Yanan Wang <wangyanan55@...wei.com>,
        Aaron Lewis <aaronlewis@...gle.com>,
        Jim Mattson <jmattson@...gle.com>,
        Oliver Upton <oupton@...gle.com>,
        Vitaly Kuznetsov <vkuznets@...hat.com>,
        Peter Shier <pshier@...gle.com>,
        Axel Rasmussen <axelrasmussen@...gle.com>,
        Zhenzhong Duan <zhenzhong.duan@...el.com>,
        "Maciej S. Szmigiero" <maciej.szmigiero@...cle.com>,
        Like Xu <like.xu@...ux.intel.com>,
        open list <linux-kernel@...r.kernel.org>,
        "open list:KERNEL VIRTUAL MACHINE (KVM)" <kvm@...r.kernel.org>
Subject: Re: [RFC PATCH 1/4] KVM: selftests: Add support for creating
 non-default type VMs

On Wed, Aug 04, 2021, Erdem Aktas wrote:
> Thank you all for all that great feedback! I will include them in my v2.
> 
> On Wed, Aug 4, 2021 at 7:46 AM Maxim Levitsky <mlevitsk@...hat.com> wrote:
> >
> > > > > Can we pass KVM_X86_LEGACY_VM (whatever name when it's upstreamed)
> > > > > instead of 0?
> > > >
> I was originally thinking of doing this but Sean has suggested that we
> should use 0 to make it  arch-agnostic for creating default VMs.
> +Sean Christopherson : What do you think?

I hate passing '0', but KVM_X86_LEGACY_VM is worse because it's nonsensical for
other architectures.
 
> >
> > KVM_X86_NORMAL_VM is a very good name IMHO as well.

But that implies protected guests are abnormal!  And KVM_X86_STANDARD_VM would
imply protected guests are sub-standard!  I'm only half-joking, e.g. if we get
to the point where the majority of guests being run are protected guests, then
!protected guests are no longer the "standard".

Looking at other architectures, I think the least awful option is a generic
KVM_VM_TYPE_AUTO, or maybe KVM_VM_TYPE_DEFAULT.  That aligns with how '0' is used
by PPC, MIPS, and arm64[*], and would work for x86 as well without implying what's
normal/standard.

[*] arm64 uses the type to specify the IPA width (I'm not even sure what that is),
    but thankfully interprets '0' as a default.