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

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Date:   Tue, 10 Jul 2018 07:21:41 -0400
From:   Konrad Rzeszutek Wilk <konrad.wilk@...cle.com>
To:     "Kirill A. Shutemov" <kirill@...temov.name>
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 July 10, 2018 6:49:10 AM EDT, "Kirill A. Shutemov" <kirill@...temov.name> wrote:
>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.

Perhaps you can then remove the "." and join the sentences 
>
>> > 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
>> > 
>>