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

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Date:   Mon, 9 Jul 2018 14:20:55 -0400
From:   Konrad Rzeszutek Wilk <konrad.wilk@...cle.com>
To:     "Kirill A. Shutemov" <kirill.shutemov@...ux.intel.com>
Cc:     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 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?
> 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
>