linux-kernel - Re: [PATCH, RFC 49/62] mm, x86: export several MKTME variables

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Date:   Mon, 17 Jun 2019 09:46:43 +0200
From:   Peter Zijlstra <peterz@...radead.org>
To:     Kai Huang <kai.huang@...ux.intel.com>
Cc:     "Kirill A. Shutemov" <kirill.shutemov@...ux.intel.com>,
        Andrew Morton <akpm@...ux-foundation.org>, x86@...nel.org,
        Thomas Gleixner <tglx@...utronix.de>,
        Ingo Molnar <mingo@...hat.com>,
        "H. Peter Anvin" <hpa@...or.com>, Borislav Petkov <bp@...en8.de>,
        Andy Lutomirski <luto@...capital.net>,
        David Howells <dhowells@...hat.com>,
        Kees Cook <keescook@...omium.org>,
        Dave Hansen <dave.hansen@...el.com>,
        Jacob Pan <jacob.jun.pan@...ux.intel.com>,
        Alison Schofield <alison.schofield@...el.com>,
        linux-mm@...ck.org, kvm@...r.kernel.org, keyrings@...r.kernel.org,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH, RFC 49/62] mm, x86: export several MKTME variables

On Mon, Jun 17, 2019 at 03:14:29PM +1200, Kai Huang wrote:
> On Fri, 2019-06-14 at 13:56 +0200, Peter Zijlstra wrote:
> > On Wed, May 08, 2019 at 05:44:09PM +0300, Kirill A. Shutemov wrote:
> > > From: Kai Huang <kai.huang@...ux.intel.com>
> > > 
> > > KVM needs those variables to get/set memory encryption mask.
> > > 
> > > Signed-off-by: Kai Huang <kai.huang@...ux.intel.com>
> > > Signed-off-by: Kirill A. Shutemov <kirill.shutemov@...ux.intel.com>
> > > ---
> > >  arch/x86/mm/mktme.c | 3 +++
> > >  1 file changed, 3 insertions(+)
> > > 
> > > diff --git a/arch/x86/mm/mktme.c b/arch/x86/mm/mktme.c
> > > index df70651816a1..12f4266cf7ea 100644
> > > --- a/arch/x86/mm/mktme.c
> > > +++ b/arch/x86/mm/mktme.c
> > > @@ -7,13 +7,16 @@
> > >  
> > >  /* Mask to extract KeyID from physical address. */
> > >  phys_addr_t mktme_keyid_mask;
> > > +EXPORT_SYMBOL_GPL(mktme_keyid_mask);
> > >  /*
> > >   * Number of KeyIDs available for MKTME.
> > >   * Excludes KeyID-0 which used by TME. MKTME KeyIDs start from 1.
> > >   */
> > >  int mktme_nr_keyids;
> > > +EXPORT_SYMBOL_GPL(mktme_nr_keyids);
> > >  /* Shift of KeyID within physical address. */
> > >  int mktme_keyid_shift;
> > > +EXPORT_SYMBOL_GPL(mktme_keyid_shift);
> > >  
> > >  DEFINE_STATIC_KEY_FALSE(mktme_enabled_key);
> > >  EXPORT_SYMBOL_GPL(mktme_enabled_key);
> > 
> > NAK, don't export variables. Who owns the values, who enforces this?
> > 
> 
> Both KVM and IOMMU driver need page_keyid() and mktme_keyid_shift to set page's keyID to the right
> place in the PTE (of KVM EPT and VT-d DMA page table).
> 
> MKTME key type code need to know mktme_nr_keyids in order to alloc/free keyID.
> 
> Maybe better to introduce functions instead of exposing variables directly?
> 
> Or instead of introducing page_keyid(), we use page_encrypt_mask(), which essentially holds
> "page_keyid() << mktme_keyid_shift"?

Yes, that's much better, because that strictly limits the access to R/O.