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Subject: Re: [PATCH 00/23] KAISER: unmap most of the kernel from userspace
 page tables
To: Dave Hansen <dave.hansen@linux.intel.com>,
        Linus Torvalds <torvalds@linux-foundation.org>,
        Andy Lutomirski <luto@kernel.org>
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Cc: Linux Kernel Mailing List <linux-kernel@vger.kernel.org>,
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        Hugh Dickins <hughd@google.com>
From: Dave Hansen <dave.hansen@intel.com>
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Date: Tue, 31 Oct 2017 17:21:56 -0700
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On 10/31/2017 04:44 PM, Dave Hansen wrote:
>>      That seems insane. Why isn't only tyhe top level shadowed, and
>> then lower levels are shared between the shadowed and the "kernel"
>> page tables?
> There are obviously two PGDs.  The userspace half of the PGD is an exact
> copy so all the lower levels are shared.  You can see this bit in the
> memcpy that we do in clone_pgd_range().

This is wrong.

The userspace copying is done via the code we add to native_set_pgd().
Whenever we set the kernel PGD, we also make sure to make a
corresponding entry in the user/shadow PGD.

The memcpy() that I was talking about does the kernel portion of the PGD.