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Subject: Re: [PATCHv5 02/19] mm: Do not use zero page in encrypted pages
References: <20180717112029.42378-1-kirill.shutemov@linux.intel.com>
 <20180717112029.42378-3-kirill.shutemov@linux.intel.com>
From: Dave Hansen <dave.hansen@intel.com>
Message-ID: <e09c67ab-38a7-5b76-29e6-a45627eec1e5@intel.com>
Date: Wed, 18 Jul 2018 10:36:24 -0700
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To: "Kirill A. Shutemov" <kirill.shutemov@linux.intel.com>, Ingo Molnar <mingo@redhat.com>, x86@kernel.org, Thomas Gleixner <tglx@linutronix.de>, "H. Peter Anvin" <hpa@zytor.com>, Tom Lendacky <thomas.lendacky@amd.com>
Cc: Kai Huang <kai.huang@linux.intel.com>, Jacob Pan <jacob.jun.pan@linux.intel.com>, linux-kernel@vger.kernel.org, linux-mm@kvack.org

On 07/17/2018 04:20 AM, Kirill A. Shutemov wrote:
> Zero page is not encrypted and putting it into encrypted VMA produces
> garbage.
> 
> We can map zero page with KeyID-0 into an encrypted VMA, but this would
> be violation security boundary between encryption domains.

Why?  How is it a violation?

It only matters if they write secrets.  They can't write secrets to the
zero page.

Is this only because you accidentally inherited ->vm_page_prot on the
zero page PTE?