linux-kernel - Re: [RFC PATCH 03/13] kvm: Add XO memslot type

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Message-ID: <5201724e-bded-1af1-7f46-0f3e1763c797@redhat.com>
Date:   Fri, 4 Oct 2019 09:27:09 +0200
From:   Paolo Bonzini <pbonzini@...hat.com>
To:     Rick Edgecombe <rick.p.edgecombe@...el.com>, kvm@...r.kernel.org,
        linux-kernel@...r.kernel.org, x86@...nel.org, linux-mm@...ck.org,
        luto@...nel.org, peterz@...radead.org, dave.hansen@...el.com,
        sean.j.christopherson@...el.com, keescook@...omium.org
Cc:     kristen@...ux.intel.com, deneen.t.dock@...el.com,
        Yu Zhang <yu.c.zhang@...ux.intel.com>
Subject: Re: [RFC PATCH 03/13] kvm: Add XO memslot type

On 03/10/19 23:23, Rick Edgecombe wrote:
> Add XO memslot type to create execute-only guest physical memory based on
> the RO memslot. Like the RO memslot, disallow changing the memslot type
> to/from XO.
> 
> In the EPT case ACC_USER_MASK represents the readable bit, so add the
> ability for set_spte() to unset this.
> 
> This is based in part on a patch by Yu Zhang.
> 
> Signed-off-by: Yu Zhang <yu.c.zhang@...ux.intel.com>
> Signed-off-by: Rick Edgecombe <rick.p.edgecombe@...el.com>

Instead of this, why not check the exit qualification gpa and, if it has
the XO bit set, mask away both the XO bit and the R bit?  It can be done
unconditionally for all memslots.  This should require no change to
userspace.

Paolo