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

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Date:   Thu, 23 Feb 2017 17:12:38 -0600
From:   Tom Lendacky <thomas.lendacky@....com>
To:     Dave Hansen <dave.hansen@...el.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 2/22/2017 12:13 PM, Dave Hansen wrote:
> 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)?

I think that's a good catch.  Let me look at it, but I believe that it
should be possible to do and avoid what you're worried about below.

Thanks,
Tom

>
> 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.
>