linux-kernel - Re: [RFC, PATCH 07/22] x86/mm: Mask out KeyID bits from page table entry pfn

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Message-ID: <87woy414vt.fsf@e105922-lin.cambridge.arm.com>
Date:   Thu, 22 Mar 2018 15:55:50 +0000
From:   Punit Agrawal <punit.agrawal@....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>,
        linux-kernel@...r.kernel.org, linux-mm@...ck.org
Subject: Re: [RFC, PATCH 07/22] x86/mm: Mask out KeyID bits from page table entry pfn

Hi Kirill,

A flyby comment below.

"Kirill A. Shutemov" <kirill.shutemov@...ux.intel.com> writes:

> MKTME claims several upper bits of the physical address in a page table
> entry to encode KeyID. It effectively shrinks number of bits for
> physical address. We should exclude KeyID bits from physical addresses.
>
> For instance, if CPU enumerates 52 physical address bits and number of
> bits claimed for KeyID is 6, bits 51:46 must not be threated as part
> physical address.
>
> This patch adjusts __PHYSICAL_MASK during MKTME enumeration.
>
> Signed-off-by: Kirill A. Shutemov <kirill.shutemov@...ux.intel.com>
> ---
>  arch/x86/kernel/cpu/intel.c | 24 ++++++++++++++++++++++++
>  1 file changed, 24 insertions(+)
>
> diff --git a/arch/x86/kernel/cpu/intel.c b/arch/x86/kernel/cpu/intel.c
> index c770689490b5..35436bbadd0b 100644
> --- a/arch/x86/kernel/cpu/intel.c
> +++ b/arch/x86/kernel/cpu/intel.c
> @@ -580,6 +580,30 @@ static void detect_tme(struct cpuinfo_x86 *c)
>  		mktme_status = MKTME_ENABLED;
>  	}
>  
> +#ifdef CONFIG_X86_INTEL_MKTME
> +	if (mktme_status == MKTME_ENABLED && nr_keyids) {
> +		/*
> +		 * Mask out bits claimed from KeyID from physical address mask.
> +		 *
> +		 * For instance, if a CPU enumerates 52 physical address bits
> +		 * and number of bits claimed for KeyID is 6, bits 51:46 of
> +		 * physical address is unusable.
> +		 */
> +		phys_addr_t keyid_mask;
> +
> +		keyid_mask = 1ULL << c->x86_phys_bits;
> +		keyid_mask -= 1ULL << (c->x86_phys_bits - keyid_bits);
> +		physical_mask &= ~keyid_mask;

You could use GENMASK_ULL() to construct the keyid_mask instead of
rolling your own here.

Thanks,
Punit


> +	} else {
> +		/*
> +		 * Reset __PHYSICAL_MASK.
> +		 * Maybe needed if there's inconsistent configuation
> +		 * between CPUs.
> +		 */
> +		physical_mask = (1ULL << __PHYSICAL_MASK_SHIFT) - 1;
> +	}
> +#endif
> +
>  	/*
>  	 * Exclude KeyID bits from physical address bits.
>  	 *