linux-kernel - Re: [PATCH 12/31] x86/entry/32: Add PTI cr3 switch to non-NMI entry/exit points

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Message-ID: <7727356a-7266-1166-1903-c4ebc0002299@intel.com>
Date:   Thu, 1 Mar 2018 10:36:21 -0800
From:   Dave Hansen <dave.hansen@...el.com>
To:     Brian Gerst <brgerst@...il.com>, Joerg Roedel <jroedel@...e.de>
Cc:     Waiman Long <longman@...hat.com>, Joerg Roedel <joro@...tes.org>,
        Thomas Gleixner <tglx@...utronix.de>,
        Ingo Molnar <mingo@...nel.org>,
        "H . Peter Anvin" <hpa@...or.com>,
        the arch/x86 maintainers <x86@...nel.org>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        Linux-MM <linux-mm@...ck.org>,
        Linus Torvalds <torvalds@...ux-foundation.org>,
        Andy Lutomirski <luto@...nel.org>,
        Josh Poimboeuf <jpoimboe@...hat.com>,
        Juergen Gross <jgross@...e.com>,
        Peter Zijlstra <peterz@...radead.org>,
        Borislav Petkov <bp@...en8.de>, Jiri Kosina <jkosina@...e.cz>,
        Boris Ostrovsky <boris.ostrovsky@...cle.com>,
        David Laight <David.Laight@...lab.com>,
        Denys Vlasenko <dvlasenk@...hat.com>,
        Eduardo Valentin <eduval@...zon.com>,
        Greg KH <gregkh@...uxfoundation.org>,
        Will Deacon <will.deacon@....com>,
        "Liguori, Anthony" <aliguori@...zon.com>,
        Daniel Gruss <daniel.gruss@...k.tugraz.at>,
        Hugh Dickins <hughd@...gle.com>,
        Kees Cook <keescook@...gle.com>,
        Andrea Arcangeli <aarcange@...hat.com>,
        Waiman Long <llong@...hat.com>, Pavel Machek <pavel@....cz>
Subject: Re: [PATCH 12/31] x86/entry/32: Add PTI cr3 switch to non-NMI
 entry/exit points

On 03/01/2018 10:24 AM, Brian Gerst wrote:
> One thing that I am not certain about is whether debug exception can
> happen even if the IF flag is cleared. If it can, debug exception should
> be handled like NMI as the state of the CR3 can be indeterminate if the
> exception happens in the entry/exit code.

It can happen with IF cleared.  I ran into it during PTI development
more than once.  That's why the debug fault code uses paranoid_entry on
64-bit just like the NMI code.