linux-kernel - Re: [RFC PATCH v4 07/28] x86: Provide general kernel support for memory encryption

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Message-ID: <a3f56612-396e-b230-d909-93a7128ea2fc@intel.com>
Date:   Wed, 22 Feb 2017 10:13:00 -0800
From:   Dave Hansen <dave.hansen@...el.com>
To:     Tom Lendacky <thomas.lendacky@....com>, linux-arch@...r.kernel.org,
        linux-efi@...r.kernel.org, kvm@...r.kernel.org,
        linux-doc@...r.kernel.org, x86@...nel.org,
        linux-kernel@...r.kernel.org, kasan-dev@...glegroups.com,
        linux-mm@...ck.org, iommu@...ts.linux-foundation.org
Cc:     Rik van Riel <riel@...hat.com>,
        Radim Krčmář <rkrcmar@...hat.com>,
        Toshimitsu Kani <toshi.kani@....com>,
        Arnd Bergmann <arnd@...db.de>,
        Jonathan Corbet <corbet@....net>,
        Matt Fleming <matt@...eblueprint.co.uk>,
        "Michael S. Tsirkin" <mst@...hat.com>,
        Joerg Roedel <joro@...tes.org>,
        Konrad Rzeszutek Wilk <konrad.wilk@...cle.com>,
        Paolo Bonzini <pbonzini@...hat.com>,
        Brijesh Singh <brijesh.singh@....com>,
        Ingo Molnar <mingo@...hat.com>,
        Alexander Potapenko <glider@...gle.com>,
        Andy Lutomirski <luto@...nel.org>,
        "H. Peter Anvin" <hpa@...or.com>, Borislav Petkov <bp@...en8.de>,
        Andrey Ryabinin <aryabinin@...tuozzo.com>,
        Thomas Gleixner <tglx@...utronix.de>,
        Larry Woodman <lwoodman@...hat.com>,
        Dmitry Vyukov <dvyukov@...gle.com>
Subject: Re: [RFC PATCH v4 07/28] x86: Provide general kernel support for
 memory encryption

On 02/16/2017 07:43 AM, Tom Lendacky wrote:
>  static inline unsigned long pte_pfn(pte_t pte)
>  {
> -	return (pte_val(pte) & PTE_PFN_MASK) >> PAGE_SHIFT;
> +	return (pte_val(pte) & ~sme_me_mask & PTE_PFN_MASK) >> PAGE_SHIFT;
>  }
>  
>  static inline unsigned long pmd_pfn(pmd_t pmd)
>  {
> -	return (pmd_val(pmd) & pmd_pfn_mask(pmd)) >> PAGE_SHIFT;
> +	return (pmd_val(pmd) & ~sme_me_mask & pmd_pfn_mask(pmd)) >> PAGE_SHIFT;
>  }

Could you talk a bit about why you chose to do the "~sme_me_mask" bit in
here instead of making it a part of PTE_PFN_MASK / pmd_pfn_mask(pmd)?

It might not matter, but I'd be worried that this ends up breaking
direct users of PTE_PFN_MASK / pmd_pfn_mask(pmd) since they now no
longer mask the PFN out of a PTE.