linux-kernel - Re: [PATCH v5 07/17] KVM: x86: add fields to struct kvm

lists.openwall.net		lists / announce owl-users owl-dev john-users john-dev passwdqc-users yescrypt popa3d-users / oss-security kernel-hardening musl sabotage tlsify passwords / crypt-dev xvendor / Bugtraq Full-Disclosure linux-kernel linux-netdev linux-ext4 linux-hardening linux-cve-announce PHC
Open Source and information security mailing list archives

Hash Suite: Windows password security audit tool. GUI, reports in PDF.

[<prev] [next>] [<thread-prev] [thread-next>] [day] [month] [year] [list]

Message-ID: <ZhVeJH0DPL89Dg97@google.com>
Date: Tue, 9 Apr 2024 08:26:28 -0700
From: Sean Christopherson <seanjc@...gle.com>
To: Paolo Bonzini <pbonzini@...hat.com>
Cc: Rick P Edgecombe <rick.p.edgecombe@...el.com>, "kvm@...r.kernel.org" <kvm@...r.kernel.org>, 
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>, 
	"michael.roth@....com" <michael.roth@....com>, Isaku Yamahata <isaku.yamahata@...el.com>
Subject: Re: [PATCH v5 07/17] KVM: x86: add fields to struct kvm_arch for CoCo features

On Tue, Apr 09, 2024, Paolo Bonzini wrote:
> On Tue, Apr 9, 2024 at 3:21 AM Sean Christopherson <seanjc@...glecom> wrote:
> > > I'm a little late to this conversation, so hopefully not just complicating
> > > things. But why not deduce has_private_mem and has_protected_state from the
> > > vm_type during runtime? Like if kvm.arch.vm_type was instead a bit mask with
> > > the bit position of the KVM_X86_*_VM set, kvm_arch_has_private_mem() could
> > > bitwise-and with a compile time mask of vm_types that have primate memory.
> > > This also prevents it from ever transitioning through non-nonsensical states
> > > like vm_type == KVM_X86_TDX_VM, but !has_private_memory, so would be a little
> > > more robust.
> >
> > LOL, time is a circle, or something like that.  Paolo actually did this in v2[*],
> > and I objected, vociferously.
> 
> To be fair, Rick is asking for something much less hideous - just set
> 
>  kvm->arch.vm_type = (1 << vm_type);
> 
> and then define kvm_has_*(kvm) as !!(kvm->arch.vm_type & SOME_BIT_MASK).
> 
> And indeed it makes sense as an alternative.

Ah, yeah, I'd be fine with that. 

> It also feels a little bit more restrictive and the benefit is small, so I
> think I'm going to go with this version.

+1