From mboxrd@z Thu Jan  1 00:00:00 1970
Return-Path: <linux-kernel-owner@vger.kernel.org>
Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand
        id S1753910AbdK0Rdo (ORCPT <rfc822;w@1wt.eu>);
        Mon, 27 Nov 2017 12:33:44 -0500
Received: from Galois.linutronix.de ([146.0.238.70]:56934 "EHLO
        Galois.linutronix.de" rhost-flags-OK-OK-OK-OK) by vger.kernel.org
        with ESMTP id S1752635AbdK0Rdn (ORCPT
        <rfc822;linux-kernel@vger.kernel.org>);
        Mon, 27 Nov 2017 12:33:43 -0500
Date: Mon, 27 Nov 2017 18:33:39 +0100 (CET)
From: Thomas Gleixner <tglx@linutronix.de>
To: Peter Zijlstra <peterz@infradead.org>
cc: Ingo Molnar <mingo@kernel.org>, linux-kernel@vger.kernel.org,
        Dave Hansen <dave.hansen@linux.intel.com>,
        Andy Lutomirski <luto@amacapital.net>,
        "H . Peter Anvin" <hpa@zytor.com>, Borislav Petkov <bp@alien8.de>,
        Linus Torvalds <torvalds@linux-foundation.org>
Subject: Re: [PATCH 02/24] x86/mm/kaiser: Prepare the x86/entry assembly code
 for entry/exit CR3 switching
In-Reply-To: <20171127173146.plbdbiuzkv5ctgw6@hirez.programming.kicks-ass.net>
Message-ID: <alpine.DEB.2.20.1711271832590.1799@nanos>
References: <20171127104923.14378-1-mingo@kernel.org> <20171127104923.14378-3-mingo@kernel.org> <20171127173146.plbdbiuzkv5ctgw6@hirez.programming.kicks-ass.net>
User-Agent: Alpine 2.20 (DEB 67 2015-01-07)
MIME-Version: 1.0
Content-Type: text/plain; charset=US-ASCII
Sender: linux-kernel-owner@vger.kernel.org
List-ID: <linux-kernel.vger.kernel.org>
X-Mailing-List: linux-kernel@vger.kernel.org

On Mon, 27 Nov 2017, Peter Zijlstra wrote:
> On Mon, Nov 27, 2017 at 11:49:01AM +0100, Ingo Molnar wrote:
> > diff --git a/arch/x86/entry/entry_64.S b/arch/x86/entry/entry_64.S
> > index caf74a1bb3de..df0152bee8a8 100644
> 
> > @@ -198,6 +201,14 @@ ENTRY(entry_SYSCALL_64)
> >  
> >  	swapgs
> >  	movq	%rsp, PER_CPU_VAR(rsp_scratch)
> > +
> > +	/*
> > +	 * The kernel CR3 is needed to map the process stack, but we
> > +	 * need a scratch register to be able to load CR3.  %rsp is
> > +	 * clobberable right now, so use it as a scratch register.
> > +	 * %rsp will look crazy here for a couple instructions.
> > +	 */
> > +	SWITCH_TO_KERNEL_CR3 scratch_reg=%rsp
> >  	movq	PER_CPU_VAR(cpu_current_top_of_stack), %rsp
> >  
> >  	/* Construct struct pt_regs on stack */
> 
> I think we can do away with this one, on account of never getting here
> because of entry_SYSCALL_64_trampoline.

It's on my list already. About 5 people noticed :)

Still trying to decode that paravirt fail.....

Thanks,

	tglx