linux-kernel - Re: [RFC PATCH 09/13] x86/cpufeature: Add detection of KVM XO

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Date:   Tue, 29 Oct 2019 23:52:08 +0000
From:   "Edgecombe, Rick P" <rick.p.edgecombe@...el.com>
To:     "keescook@...omium.org" <keescook@...omium.org>
CC:     "kvm@...r.kernel.org" <kvm@...r.kernel.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        "peterz@...radead.org" <peterz@...radead.org>,
        "Dock, Deneen T" <deneen.t.dock@...el.com>,
        "Christopherson, Sean J" <sean.j.christopherson@...el.com>,
        "linux-mm@...ck.org" <linux-mm@...ck.org>,
        "x86@...nel.org" <x86@...nel.org>,
        "kristen@...ux.intel.com" <kristen@...ux.intel.com>,
        "luto@...nel.org" <luto@...nel.org>,
        "pbonzini@...hat.com" <pbonzini@...hat.com>,
        "Hansen, Dave" <dave.hansen@...el.com>
Subject: Re: [RFC PATCH 09/13] x86/cpufeature: Add detection of KVM XO

On Tue, 2019-10-29 at 16:33 -0700, Kees Cook wrote:
> On Thu, Oct 03, 2019 at 02:23:56PM -0700, Rick Edgecombe wrote:
> > Add a new CPUID leaf to hold the contents of CPUID 0x40000030 EAX to
> > detect KVM defined generic VMM features.
> > 
> > The leaf was proposed to allow KVM to communicate features that are
> > defined by KVM, but available for any VMM to implement.
> > 
> > Add cpu_feature_enabled() support for features in this leaf (KVM XO), and
> > a pgtable_kvmxo_enabled() helper similar to pgtable_l5_enabled() so that
> > pgtable_kvmxo_enabled() can be used in early code that includes
> > arch/x86/include/asm/sparsemem.h.
> > 
> > Lastly, in head64.c detect and this feature and perform necessary
> > adjustments to physical_mask.
> 
> Can this be exposed to /proc/cpuinfo so a guest userspace can determine
> if this feature is enabled?
> 
> -Kees

Is there a good place to expose the information that the PROT_EXEC and
!PROT_READ combo creates execute-only memory? This way apps can check one place
for the support and not worry about the implementation whether it's this, x86
pkeys, arm or other.