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Subject: Re: [PATCH 12/31] x86/entry/32: Add PTI cr3 switch to non-NMI
 entry/exit points
To: Brian Gerst <brgerst@gmail.com>, Joerg Roedel <jroedel@suse.de>
References: <1518168340-9392-1-git-send-email-joro@8bytes.org>
 <1518168340-9392-13-git-send-email-joro@8bytes.org>
 <afd5bae9-f53e-a225-58f1-4ba2422044e3@redhat.com>
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Cc: Waiman Long <longman@redhat.com>, Joerg Roedel <joro@8bytes.org>,
 Thomas Gleixner <tglx@linutronix.de>, Ingo Molnar <mingo@kernel.org>,
 "H . Peter Anvin" <hpa@zytor.com>, the arch/x86 maintainers
 <x86@kernel.org>, Linux Kernel Mailing List <linux-kernel@vger.kernel.org>,
 Linux-MM <linux-mm@kvack.org>, Linus Torvalds
 <torvalds@linux-foundation.org>, Andy Lutomirski <luto@kernel.org>,
 Josh Poimboeuf <jpoimboe@redhat.com>, Juergen Gross <jgross@suse.com>,
 Peter Zijlstra <peterz@infradead.org>, Borislav Petkov <bp@alien8.de>,
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 David Laight <David.Laight@aculab.com>, Denys Vlasenko
 <dvlasenk@redhat.com>, Eduardo Valentin <eduval@amazon.com>,
 Greg KH <gregkh@linuxfoundation.org>, Will Deacon <will.deacon@arm.com>,
 "Liguori, Anthony" <aliguori@amazon.com>,
 Daniel Gruss <daniel.gruss@iaik.tugraz.at>, Hugh Dickins <hughd@google.com>,
 Kees Cook <keescook@google.com>, Andrea Arcangeli <aarcange@redhat.com>,
 Waiman Long <llong@redhat.com>, Pavel Machek <pavel@ucw.cz>
From: Dave Hansen <dave.hansen@intel.com>
Message-ID: <7727356a-7266-1166-1903-c4ebc0002299@intel.com>
Date: Thu, 1 Mar 2018 10:36:21 -0800
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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.