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Date: Sun, 22 Nov 2020 13:44:53 -0800 From: Andy Lutomirski <luto@...nel.org> To: Jürgen Groß <jgross@...e.com> Cc: Peter Zijlstra <peterz@...radead.org>, Stefano Stabellini <sstabellini@...nel.org>, "VMware, Inc." <pv-drivers@...are.com>, X86 ML <x86@...nel.org>, LKML <linux-kernel@...r.kernel.org>, Linux Virtualization <virtualization@...ts.linux-foundation.org>, Ingo Molnar <mingo@...hat.com>, Borislav Petkov <bp@...en8.de>, Andrew Lutomirski <luto@...nel.org>, "H. Peter Anvin" <hpa@...or.com>, xen-devel <xen-devel@...ts.xenproject.org>, Thomas Gleixner <tglx@...utronix.de>, Boris Ostrovsky <boris.ostrovsky@...cle.com> Subject: Re: [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@...e.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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