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

[Kai Huang]

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@xxxxxxxxxxxxxxx>
> > 
> > KVM needs those variables to get/set memory encryption mask.
> > 
> > Signed-off-by: Kai Huang <kai.huang@xxxxxxxxxxxxxxx>
> > Signed-off-by: Kirill A. Shutemov <kirill.shutemov@xxxxxxxxxxxxxxx>
> > ---
> >  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"?

Thanks,
-Kai