linux-kernel - Re: [RFC PATCH V3 2/4] KVM: X86: Introduce role.glevel for level expanded pagetable

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]

Date:   Wed, 13 Apr 2022 12:13:27 +0800
From:   Lai Jiangshan <jiangshanlai@...il.com>
To:     Sean Christopherson <seanjc@...gle.com>
Cc:     LKML <linux-kernel@...r.kernel.org>, kvm@...r.kernel.org,
        Paolo Bonzini <pbonzini@...hat.com>,
        Lai Jiangshan <jiangshan.ljs@...group.com>,
        Jonathan Corbet <corbet@....net>,
        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>,
        Dave Hansen <dave.hansen@...ux.intel.com>,
        X86 ML <x86@...nel.org>, "H. Peter Anvin" <hpa@...or.com>,
        linux-doc@...r.kernel.org
Subject: Re: [RFC PATCH V3 2/4] KVM: X86: Introduce role.glevel for level
 expanded pagetable

On Wed, Apr 13, 2022 at 5:31 AM Sean Christopherson <seanjc@...gle.com> wrote:

> >  union kvm_mmu_page_role {
> >       u32 word;
> > @@ -331,7 +331,8 @@ union kvm_mmu_page_role {
> >               unsigned smap_andnot_wp:1;
> >               unsigned ad_disabled:1;
> >               unsigned guest_mode:1;
> > -             unsigned :6;
> > +             unsigned glevel:4;
>
> We don't need 4 bits for this.  Crossing our fingers that we never had to shadow
> a 2-level guest with a 6-level host, we can do:
>
>                 unsigned passthrough_delta:2;

We can save the bits in the future when we need more bits so I didn't
hesitate to use 4 bits since glevel gives simple code. ^_^

I think the name passthrough_delta is more informative and glevel
is used only for comparison so passthrough_delta can also be
simple.  I will apply your suggestion.


Thanks
Lai