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Subject: Re: [RFC PATCH v4 07/28] x86: Provide general kernel support for
 memory encryption
References: <20170216154158.19244.66630.stgit@tlendack-t1.amdoffice.net>
 <20170216154332.19244.55451.stgit@tlendack-t1.amdoffice.net>
From: Dave Hansen <dave.hansen@intel.com>
Message-ID: <a3f56612-396e-b230-d909-93a7128ea2fc@intel.com>
Date: Wed, 22 Feb 2017 10:13:00 -0800
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To: Tom Lendacky <thomas.lendacky@amd.com>, linux-arch@vger.kernel.org, linux-efi@vger.kernel.org, kvm@vger.kernel.org, linux-doc@vger.kernel.org, x86@kernel.org, linux-kernel@vger.kernel.org, kasan-dev@googlegroups.com, linux-mm@kvack.org, iommu@lists.linux-foundation.org
Cc: Rik van Riel <riel@redhat.com>, =?UTF-8?B?UmFkaW0gS3LEjW3DocWZ?= <rkrcmar@redhat.com>, Toshimitsu Kani <toshi.kani@hpe.com>, Arnd Bergmann <arnd@arndb.de>, Jonathan Corbet <corbet@lwn.net>, Matt Fleming <matt@codeblueprint.co.uk>, "Michael S. Tsirkin" <mst@redhat.com>, Joerg Roedel <joro@8bytes.org>, Konrad Rzeszutek Wilk <konrad.wilk@oracle.com>, Paolo Bonzini <pbonzini@redhat.com>, Brijesh Singh <brijesh.singh@amd.com>, Ingo Molnar <mingo@redhat.com>, Alexander Potapenko <glider@google.com>, Andy Lutomirski <luto@kernel.org>, "H. Peter Anvin" <hpa@zytor.com>, Borislav Petkov <bp@alien8.de>, Andrey Ryabinin <aryabinin@virtuozzo.com>, Thomas Gleixner <tglx@linutronix.de>, Larry Woodman <lwoodman@redhat.com>, Dmitry Vyukov <dvyukov@google.com>

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.

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