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Date: Wed, 18 Jul 2018 13:59:05 +0200
From: Joerg Roedel <joro@8bytes.org>
Subject: Re: [PATCH 10/39] x86/entry/32: Handle Entry from Kernel-Mode on
 Entry-Stack
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To: Andy Lutomirski <luto@amacapital.net>
Cc: Joerg Roedel <jroedel@suse.de>, Andy Lutomirski <luto@kernel.org>, Thomas Gleixner <tglx@linutronix.de>, Ingo Molnar <mingo@kernel.org>, "H . Peter Anvin" <hpa@zytor.com>, X86 ML <x86@kernel.org>, LKML <linux-kernel@vger.kernel.org>, Linux-MM <linux-mm@kvack.org>, Linus Torvalds <torvalds@linux-foundation.org>, Dave Hansen <dave.hansen@intel.com>, Josh Poimboeuf <jpoimboe@redhat.com>, Juergen Gross <jgross@suse.com>, Peter Zijlstra <peterz@infradead.org>, Borislav Petkov <bp@alien8.de>, Jiri Kosina <jkosina@suse.cz>, Boris Ostrovsky <boris.ostrovsky@oracle.com>, Brian Gerst <brgerst@gmail.com>, 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>, "David H . Gutteridge" <dhgutteridge@sympatico.ca>

On Tue, Jul 17, 2018 at 01:06:11PM -0700, Andy Lutomirski wrote:
> Yes, we obviously need to restore the correct cr3.  But I really don't
> like the code that rewrites the stack frame that we're about to IRET
> to, especially when it doesn't seem to serve a purpose.  I'd much
> rather the code just get its CR3 right and do the IRET and trust that
> the frame it's returning to is still there.

Okay, I'll give it a try and if it works without the copying we can put
that on-top of this patch-set. This also has the benefit that we can
revert it later if it causes problems down the road.


Regards,

	Joerg