linux-kernel - Re: [PATCH 01/23] x86, kaiser: prepare assembly for entry/exit CR3 switching

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Message-ID: <d85395ea-d848-6dd6-4e4d-d2ddba521bac@linux.intel.com>
Date:   Tue, 31 Oct 2017 18:08:33 -0700
From:   Dave Hansen <dave.hansen@...ux.intel.com>
To:     Brian Gerst <brgerst@...il.com>
Cc:     Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        Linux-MM <linux-mm@...ck.org>, moritz.lipp@...k.tugraz.at,
        daniel.gruss@...k.tugraz.at, michael.schwarz@...k.tugraz.at,
        Andy Lutomirski <luto@...nel.org>,
        Linus Torvalds <torvalds@...ux-foundation.org>,
        Kees Cook <keescook@...gle.com>, hughd@...gle.com,
        the arch/x86 maintainers <x86@...nel.org>
Subject: Re: [PATCH 01/23] x86, kaiser: prepare assembly for entry/exit CR3
 switching

On 10/31/2017 05:43 PM, Brian Gerst wrote:
>>
>> +       RESTORE_CR3 save_reg=%r14
>> +
>>         testl   %ebx, %ebx                      /* swapgs needed? */
>>         jnz     nmi_restore
>>  nmi_swapgs:
>> _
> This all needs to be conditional on a config option.  Something with
> this amount of performance impact needs to be 100% optional.

The 07/23 patch does just this.  I should have at least called that out
in the description.