linux-kernel - Re: [PATCHv4 13/18] x86/mm: Allow to disable MKTME after enumeration

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Date:   Tue, 10 Jul 2018 13:49:10 +0300
From:   "Kirill A. Shutemov" <kirill@...temov.name>
To:     Konrad Rzeszutek Wilk <konrad.wilk@...cle.com>
Cc:     "Kirill A. Shutemov" <kirill.shutemov@...ux.intel.com>,
        Ingo Molnar <mingo@...hat.com>, x86@...nel.org,
        Thomas Gleixner <tglx@...utronix.de>,
        "H. Peter Anvin" <hpa@...or.com>,
        Tom Lendacky <thomas.lendacky@....com>,
        Dave Hansen <dave.hansen@...el.com>,
        Kai Huang <kai.huang@...ux.intel.com>,
        Jacob Pan <jacob.jun.pan@...ux.intel.com>,
        linux-kernel@...r.kernel.org, linux-mm@...ck.org
Subject: Re: [PATCHv4 13/18] x86/mm: Allow to disable MKTME after enumeration

On Mon, Jul 09, 2018 at 02:20:55PM -0400, Konrad Rzeszutek Wilk wrote:
> On Tue, Jun 26, 2018 at 05:22:40PM +0300, Kirill A. Shutemov wrote:
> > The new helper mktme_disable() allows to disable MKTME even if it's
> > enumerated successfully. MKTME initialization may fail and this
> > functionality allows system to boot regardless of the failure.
> > 
> > MKTME needs per-KeyID direct mapping. It requires a lot more virtual
> > address space which may be a problem in 4-level paging mode. If the
> > system has more physical memory than we can handle with MKTME.
> 
> .. then what should happen?

We fail MKTME initialization and boot the system. See next sentence.

> > The feature allows to fail MKTME, but boot the system successfully.
> > 
> > Signed-off-by: Kirill A. Shutemov <kirill.shutemov@...ux.intel.com>
> > ---
> >  arch/x86/include/asm/mktme.h | 2 ++
> >  arch/x86/kernel/cpu/intel.c  | 5 +----
> >  arch/x86/mm/mktme.c          | 9 +++++++++
> >  3 files changed, 12 insertions(+), 4 deletions(-)
> > 
> > diff --git a/arch/x86/include/asm/mktme.h b/arch/x86/include/asm/mktme.h
> > index 44409b8bbaca..ebbee6a0c495 100644
> > --- a/arch/x86/include/asm/mktme.h
> > +++ b/arch/x86/include/asm/mktme.h
> > @@ -6,6 +6,8 @@
> >  
> >  struct vm_area_struct;
> >  
> > +void mktme_disable(void);
> > +
> >  #ifdef CONFIG_X86_INTEL_MKTME
> >  extern phys_addr_t mktme_keyid_mask;
> >  extern int mktme_nr_keyids;
> > diff --git a/arch/x86/kernel/cpu/intel.c b/arch/x86/kernel/cpu/intel.c
> > index efc9e9fc47d4..75e3b2602b4a 100644
> > --- a/arch/x86/kernel/cpu/intel.c
> > +++ b/arch/x86/kernel/cpu/intel.c
> > @@ -591,10 +591,7 @@ static void detect_tme(struct cpuinfo_x86 *c)
> >  		 * Maybe needed if there's inconsistent configuation
> >  		 * between CPUs.
> >  		 */
> > -		physical_mask = (1ULL << __PHYSICAL_MASK_SHIFT) - 1;
> > -		mktme_keyid_mask = 0;
> > -		mktme_keyid_shift = 0;
> > -		mktme_nr_keyids = 0;
> > +		mktme_disable();
> >  	}
> >  #endif
> >  
> > diff --git a/arch/x86/mm/mktme.c b/arch/x86/mm/mktme.c
> > index 1194496633ce..bb6210dbcf0e 100644
> > --- a/arch/x86/mm/mktme.c
> > +++ b/arch/x86/mm/mktme.c
> > @@ -13,6 +13,15 @@ static inline bool mktme_enabled(void)
> >  	return static_branch_unlikely(&mktme_enabled_key);
> >  }
> >  
> > +void mktme_disable(void)
> > +{
> > +	physical_mask = (1ULL << __PHYSICAL_MASK_SHIFT) - 1;
> > +	mktme_keyid_mask = 0;
> > +	mktme_keyid_shift = 0;
> > +	mktme_nr_keyids = 0;
> > +	static_branch_disable(&mktme_enabled_key);
> > +}
> > +
> >  int page_keyid(const struct page *page)
> >  {
> >  	if (!mktme_enabled())
> > -- 
> > 2.18.0
> > 
> 

-- 
 Kirill A. Shutemov