linux-kernel - Re: [PATCH 08/30] x86, kaiser: unmap kernel from userspace page tables (core patch)

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Date:   Wed, 22 Nov 2017 14:54:29 -0800
From:   Dave Hansen <dave.hansen@...ux.intel.com>
To:     Thomas Gleixner <tglx@...utronix.de>
Cc:     linux-kernel@...r.kernel.org, linux-mm@...ck.org,
        richard.fellner@...dent.tugraz.at, moritz.lipp@...k.tugraz.at,
        daniel.gruss@...k.tugraz.at, michael.schwarz@...k.tugraz.at,
        luto@...nel.org, torvalds@...ux-foundation.org,
        keescook@...gle.com, hughd@...gle.com, x86@...nel.org
Subject: Re: [PATCH 08/30] x86, kaiser: unmap kernel from userspace page
 tables (core patch)

On 11/20/2017 09:21 AM, Thomas Gleixner wrote:
>> +page tables are switched to the full "kernel" copy.  When the
>> +system switches back to user mode, the user/shadow copy is used.
>> +
>> +The minimalistic kernel portion of the user page tables try to
>> +map only what is needed to enter/exit the kernel such as the
>> +entry/exit functions themselves and the interrupt descriptor
>> +table (IDT).
> s/try to//

Actually, they do _aspire_ "to map only what is needed".  But, there
*is* some non-necessary cruft (like the first C function in an
interrupt).  So, removing this language actually makes the description
less precise.