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SubjectRe: [PATCH v2 05/12] x86: rework arch_local_irq_restore() to not use popf
On Sat, Nov 21, 2020 at 10:55 PM Jürgen Groß <jgross@suse.com> wrote:
>
> On 20.11.20 12:59, Peter Zijlstra wrote:
> > On Fri, Nov 20, 2020 at 12:46:23PM +0100, Juergen Gross wrote:
> >> +static __always_inline void arch_local_irq_restore(unsigned long flags)
> >> +{
> >> + if (!arch_irqs_disabled_flags(flags))
> >> + arch_local_irq_enable();
> >> +}
> >
> > If someone were to write horrible code like:
> >
> > local_irq_disable();
> > local_irq_save(flags);
> > local_irq_enable();
> > local_irq_restore(flags);
> >
> > we'd be up some creek without a paddle... now I don't _think_ we have
> > genius code like that, but I'd feel saver if we can haz an assertion in
> > there somewhere...
> >
> > Maybe something like:
> >
> > #ifdef CONFIG_DEBUG_ENTRY // for lack of something saner
> > WARN_ON_ONCE((arch_local_save_flags() ^ flags) & X86_EFLAGS_IF);
> > #endif
> >
> > At the end?
>
> I'd like to, but using WARN_ON_ONCE() in include/asm/irqflags.h sounds
> like a perfect receipt for include dependency hell.
>
> We could use a plain asm("ud2") instead.

How about out-of-lining it:

#ifdef CONFIG_DEBUG_ENTRY
extern void warn_bogus_irqrestore();
#endif

static __always_inline void arch_local_irq_restore(unsigned long flags)
{
if (!arch_irqs_disabled_flags(flags)) {
arch_local_irq_enable();
} else {
#ifdef CONFIG_DEBUG_ENTRY
if (unlikely(arch_local_irq_save() & X86_EFLAGS_IF))
warn_bogus_irqrestore();
#endif
}

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