linux-kernel - Re: [PATCH 1/2] x86/entry: Avoid interrupt flag save and restore

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Message-ID: <20160608121655.GA11355@gmail.com>
Date:	Wed, 8 Jun 2016 14:16:55 +0200
From:	Ingo Molnar <mingo@...nel.org>
To:	Paolo Bonzini <pbonzini@...hat.com>
Cc:	Andy Lutomirski <luto@...capital.net>,
	Thomas Gleixner <tglx@...utronix.de>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	Ingo Molnar <mingo@...nel.org.com>,
	"H. Peter Anvin" <hpa@...or.com>, X86 ML <x86@...nel.org>,
	Rik van Riel <riel@...hat.com>,
	Peter Zijlstra <peterz@...radead.org>
Subject: Re: [PATCH 1/2] x86/entry: Avoid interrupt flag save and restore


* Paolo Bonzini <pbonzini@...hat.com> wrote:

> 
> 
> On 04/06/2016 07:07, Andy Lutomirski wrote:
> > On May 30, 2016 5:30 AM, "Paolo Bonzini" <pbonzini@...hat.com> wrote:
> >>
> >> Thanks to all the work that was done by Andy Lutomirski and others,
> >> enter_from_user_mode and prepare_exit_to_usermode are now called only with
> >> interrupts disabled.  Let's provide them a version of user_enter/user_exit
> >> that skips saving and restoring the interrupt flag.
> > 
> >> +/* Called with interrupts disabled.  */
> >> +static inline void __user_enter(void)
> >> +{
> >> +       if (context_tracking_is_enabled())
> >> +               __context_tracking_enter(CONTEXT_USER);
> >> +
> >> +}
> > 
> > Would user_enter_irqs_off be a better name?
> 
> I'm just mimicking __context_tracking_enter and vs.
> context_tracking_enter.  So it is at least consistent with those functions.
> 
> The guest ones are not quite as consistent.  I can fix that later,
> there's no reason also to have guest context tracking split between
> include/linux/context_tracking.h and include/linux/kvm_host.h.

Could we please first do the cleanups before complicating the code and applying 
more substantial changes?

Doing cleanups first makes it easier to review the substantial patches as well, so 
it's a win-win.

Thanks,

	Ingo