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Date: Fri, 19 Jan 2018 10:57:05 +0100
From: Joerg Roedel <joro@8bytes.org>
Subject: Re: [PATCH 03/16] x86/entry/32: Leave the kernel via the trampoline
 stack
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To: Andy Lutomirski <luto@kernel.org>
Cc: Brian Gerst <brgerst@gmail.com>, 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>, 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>, Joerg Roedel <jroedel@suse.de>

On Wed, Jan 17, 2018 at 10:12:32AM -0800, Andy Lutomirski wrote:
> I would optimize for simplicity, not speed.  You're already planning
> to write to CR3, which is serializing, blows away the TLB, *and* takes
> the absurdly large amount of time that the microcode needs to blow
> away the TLB.

Okay, so I am going to do the stack-switch before pt_regs is restored.
This is at least better than playing games with hiding the entry/exit
%esp somewhere in stack-memory.


Thanks,

	Joerg

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