linux-kernel - Re: [PATCHv5 08/19] x86/mm: Introduce variables to store number, shift and mask of KeyIDs

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Date:   Wed, 18 Jul 2018 16:19:10 -0700
From:   Dave Hansen <dave.hansen@...el.com>
To:     "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>
Cc:     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: [PATCHv5 08/19] x86/mm: Introduce variables to store number,
 shift and mask of KeyIDs

On 07/17/2018 04:20 AM, Kirill A. Shutemov wrote:
> mktme_nr_keyids holds number of KeyIDs available for MKTME, excluding
> KeyID zero which used by TME. MKTME KeyIDs start from 1.
> 
> mktme_keyid_shift holds shift of KeyID within physical address.

I know what all these words mean, but the combination of them makes no
sense to me.  I still don't know what the variable does after reading this.

Is this the lowest bit in the physical address which is used for the
KeyID?  How many bits you must shift up a KeyID to get to the location
at which it can be masked into the physical address?

> mktme_keyid_mask holds mask to extract KeyID from physical address.

Good descriptions, wrong place.  Please put these in the code.

Also, the grammar constantly needs some work.  "holds mask" needs to be
"holds the mask".

> Signed-off-by: Kirill A. Shutemov <kirill.shutemov@...ux.intel.com>
> ---
>  arch/x86/include/asm/mktme.h | 16 ++++++++++++++++
>  arch/x86/kernel/cpu/intel.c  | 12 ++++++++----
>  arch/x86/mm/Makefile         |  2 ++
>  arch/x86/mm/mktme.c          |  5 +++++
>  4 files changed, 31 insertions(+), 4 deletions(-)
>  create mode 100644 arch/x86/include/asm/mktme.h
>  create mode 100644 arch/x86/mm/mktme.c
> 
> diff --git a/arch/x86/include/asm/mktme.h b/arch/x86/include/asm/mktme.h
> new file mode 100644
> index 000000000000..df31876ec48c
> --- /dev/null
> +++ b/arch/x86/include/asm/mktme.h
> @@ -0,0 +1,16 @@
> +#ifndef	_ASM_X86_MKTME_H
> +#define	_ASM_X86_MKTME_H
> +
> +#include <linux/types.h>
> +
> +#ifdef CONFIG_X86_INTEL_MKTME
> +extern phys_addr_t mktme_keyid_mask;
> +extern int mktme_nr_keyids;
> +extern int mktme_keyid_shift;
> +#else
> +#define mktme_keyid_mask	((phys_addr_t)0)
> +#define mktme_nr_keyids		0
> +#define mktme_keyid_shift	0
> +#endif
> +
> +#endif
> diff --git a/arch/x86/kernel/cpu/intel.c b/arch/x86/kernel/cpu/intel.c
> index bf2caf9d52dd..efc9e9fc47d4 100644
> --- a/arch/x86/kernel/cpu/intel.c
> +++ b/arch/x86/kernel/cpu/intel.c
> @@ -573,6 +573,9 @@ static void detect_tme(struct cpuinfo_x86 *c)
>  
>  #ifdef CONFIG_X86_INTEL_MKTME
>  	if (mktme_status == MKTME_ENABLED && nr_keyids) {
> +		mktme_nr_keyids = nr_keyids;
> +		mktme_keyid_shift = c->x86_phys_bits - keyid_bits;
> +
>  		/*
>  		 * Mask out bits claimed from KeyID from physical address mask.
>  		 *
> @@ -580,10 +583,8 @@ static void detect_tme(struct cpuinfo_x86 *c)
>  		 * and number of bits claimed for KeyID is 6, bits 51:46 of
>  		 * physical address is unusable.
>  		 */
> -		phys_addr_t keyid_mask;
> -
> -		keyid_mask = GENMASK_ULL(c->x86_phys_bits - 1, c->x86_phys_bits - keyid_bits);
> -		physical_mask &= ~keyid_mask;
> +		mktme_keyid_mask = GENMASK_ULL(c->x86_phys_bits - 1, mktme_keyid_shift);
> +		physical_mask &= ~mktme_keyid_mask;

Seems a bit silly that we introduce keyid_mask only to make it global a
few patches later.

>  	} else {
>  		/*
>  		 * Reset __PHYSICAL_MASK.
> @@ -591,6 +592,9 @@ static void detect_tme(struct cpuinfo_x86 *c)
>  		 * between CPUs.
>  		 */
>  		physical_mask = (1ULL << __PHYSICAL_MASK_SHIFT) - 1;
> +		mktme_keyid_mask = 0;
> +		mktme_keyid_shift = 0;
> +		mktme_nr_keyids = 0;
>  	}

Should be unnecessary.  These are zeroed by the compiler.

> diff --git a/arch/x86/mm/Makefile b/arch/x86/mm/Makefile
> index 4b101dd6e52f..4ebee899c363 100644
> --- a/arch/x86/mm/Makefile
> +++ b/arch/x86/mm/Makefile
> @@ -53,3 +53,5 @@ obj-$(CONFIG_PAGE_TABLE_ISOLATION)		+= pti.o
>  obj-$(CONFIG_AMD_MEM_ENCRYPT)	+= mem_encrypt.o
>  obj-$(CONFIG_AMD_MEM_ENCRYPT)	+= mem_encrypt_identity.o
>  obj-$(CONFIG_AMD_MEM_ENCRYPT)	+= mem_encrypt_boot.o
> +
> +obj-$(CONFIG_X86_INTEL_MKTME)	+= mktme.o
> diff --git a/arch/x86/mm/mktme.c b/arch/x86/mm/mktme.c
> new file mode 100644
> index 000000000000..467f1b26c737
> --- /dev/null
> +++ b/arch/x86/mm/mktme.c
> @@ -0,0 +1,5 @@
> +#include <asm/mktme.h>
> +
> +phys_addr_t mktme_keyid_mask;
> +int mktme_nr_keyids;
> +int mktme_keyid_shift;

Descriptions should be here, please, not in the changelog.