Re: [Xen-devel] [PATCH 5/7] x86/traps: Lift all non-entrypoint logic in entry_int82() up into C

[Wei Liu <wei.liu2@xxxxxxxxxx>]

On Wed, May 03, 2017 at 12:38:15PM +0100, Andrew Cooper wrote:
> On 03/05/17 12:26, Wei Liu wrote:
> > On Wed, May 03, 2017 at 03:02:25AM -0600, Jan Beulich wrote:
> >>>>> On 02.05.17 at 20:05, <andrew.cooper3@xxxxxxxxxx> wrote:
> >>> --- /dev/null
> >>> +++ b/xen/arch/x86/pv/traps.c
> >>> @@ -0,0 +1,44 @@
> >>> +/******************************************************************************
> >>> + * arch/x86/pv/traps.c
> >>> + *
> >>> + * PV low level entry points.
> >>> + *
> >>> + * This program is free software; you can redistribute it and/or modify
> >>> + * it under the terms of the GNU General Public License as published by
> >>> + * the Free Software Foundation; either version 2 of the License, or
> >>> + * (at your option) any later version.
> >>> + *
> >>> + * This program is distributed in the hope that it will be useful,
> >>> + * but WITHOUT ANY WARRANTY; without even the implied warranty of
> >>> + * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
> >>> + * GNU General Public License for more details.
> >>> + *
> >>> + * You should have received a copy of the GNU General Public License
> >>> + * along with this program; If not, see <http://www.gnu.org/licenses/>.
> >>> + *
> >>> + * Copyright (c) 2017 Citrix Systems Ltd.
> >>> + */
> >>> +
> >>> +#include <xen/hypercall.h>
> >>> +
> >>> +#include <asm/apic.h>
> >>> +
> >>> +#ifdef CONFIG_COMPAT
> >> As expressed before, I disagree to the re-introduction of such
> >> conditionals in x86 code.
> >>
> > I'm curious to know how the COMPAT interface is treated long term.
> >
> > I guess you're of the opinion that we should always have them enabled?
> 
> There is a valid usecase to disable CONFIG_COMPAT, seeing as sufficient
> PVH interfaces exist to start APs straight in 64bit mode, as it provides
> a meaningful reduction in hypervisor attack surface.
> 

I agree.

> As it is a configurable option, I intend to work in a direction which
> eventually makes it usable under x86.
> 
> If there is a wish to move in an opposite direction, that should be a
> separate discussion made over a patch removing its entry from
> common/Kconfig.
> 

Yes, I think a proper discussion is needed to clarify the future
direction.

Wei.

> ~Andrew

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