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

[Andrew Cooper <andrew.cooper3@xxxxxxxxxx>]

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.

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.

~Andrew

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