From: Andy Lutomirski <luto@amacapital.net> To: "Jürgen Groß" <jgross@suse.com> Cc: Andy Lutomirski <luto@kernel.org>, Peter Zijlstra <peterz@infradead.org>, Stefano Stabellini <sstabellini@kernel.org>, "VMware, Inc." <pv-drivers@vmware.com>, X86 ML <x86@kernel.org>, LKML <linux-kernel@vger.kernel.org>, Linux Virtualization <virtualization@lists.linux-foundation.org>, Ingo Molnar <mingo@redhat.com>, Borislav Petkov <bp@alien8.de>, "H. Peter Anvin" <hpa@zytor.com>, xen-devel <xen-devel@lists.xenproject.org>, Thomas Gleixner <tglx@linutronix.de>, Boris Ostrovsky <boris.ostrovsky@oracle.com> Subject: Re: [PATCH v2 05/12] x86: rework arch_local_irq_restore() to not use popf Date: Mon, 23 Nov 2020 07:15:18 -0800 [thread overview] Message-ID: <DD12CB44-457E-4FE1-8240-B334B785A93C@amacapital.net> (raw) In-Reply-To: <894a4cec-8426-4152-d391-474711040c5b@suse.com> > On Nov 22, 2020, at 9:22 PM, Jürgen Groß <jgross@suse.com> wrote: > > On 22.11.20 22:44, Andy Lutomirski wrote: >>> 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 >> } > > This couldn't be a WARN_ON_ONCE() then (or it would be a catch all). If you put the WARN_ON_ONCE in the out-of-line helper, it should work reasonably well. > Another approach might be to open-code the WARN_ON_ONCE(), like: > > #ifdef CONFIG_DEBUG_ENTRY > extern void warn_bogus_irqrestore(bool *once); > #endif > > static __always_inline void arch_local_irq_restore(unsigned long flags) > { > if (!arch_irqs_disabled_flags(flags)) > arch_local_irq_enable(); > #ifdef CONFIG_DEBUG_ENTRY > { > static bool once; > > if (unlikely(arch_local_irq_save() & X86_EFLAGS_IF)) > warn_bogus_irqrestore(&once); > } > #endif > } > I don’t know precisely what a static variable in an __always_inline function will do, but I imagine it will be, at best, erratic, especially when modules are involved. > > Juergen > <OpenPGP_0xB0DE9DD628BF132F.asc>
WARNING: multiple messages have this Message-ID (diff)
From: Andy Lutomirski <luto@amacapital.net> To: "Jürgen Groß" <jgross@suse.com> Cc: Stefano Stabellini <sstabellini@kernel.org>, Peter Zijlstra <peterz@infradead.org>, X86 ML <x86@kernel.org>, LKML <linux-kernel@vger.kernel.org>, Linux Virtualization <virtualization@lists.linux-foundation.org>, "VMware, Inc." <pv-drivers@vmware.com>, Ingo Molnar <mingo@redhat.com>, Borislav Petkov <bp@alien8.de>, Andy Lutomirski <luto@kernel.org>, "H. Peter Anvin" <hpa@zytor.com>, xen-devel <xen-devel@lists.xenproject.org>, Thomas Gleixner <tglx@linutronix.de>, Boris Ostrovsky <boris.ostrovsky@oracle.com> Subject: Re: [PATCH v2 05/12] x86: rework arch_local_irq_restore() to not use popf Date: Mon, 23 Nov 2020 07:15:18 -0800 [thread overview] Message-ID: <DD12CB44-457E-4FE1-8240-B334B785A93C@amacapital.net> (raw) In-Reply-To: <894a4cec-8426-4152-d391-474711040c5b@suse.com> > On Nov 22, 2020, at 9:22 PM, Jürgen Groß <jgross@suse.com> wrote: > > On 22.11.20 22:44, Andy Lutomirski wrote: >>> 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 >> } > > This couldn't be a WARN_ON_ONCE() then (or it would be a catch all). If you put the WARN_ON_ONCE in the out-of-line helper, it should work reasonably well. > Another approach might be to open-code the WARN_ON_ONCE(), like: > > #ifdef CONFIG_DEBUG_ENTRY > extern void warn_bogus_irqrestore(bool *once); > #endif > > static __always_inline void arch_local_irq_restore(unsigned long flags) > { > if (!arch_irqs_disabled_flags(flags)) > arch_local_irq_enable(); > #ifdef CONFIG_DEBUG_ENTRY > { > static bool once; > > if (unlikely(arch_local_irq_save() & X86_EFLAGS_IF)) > warn_bogus_irqrestore(&once); > } > #endif > } > I don’t know precisely what a static variable in an __always_inline function will do, but I imagine it will be, at best, erratic, especially when modules are involved. > > Juergen > <OpenPGP_0xB0DE9DD628BF132F.asc> _______________________________________________ Virtualization mailing list Virtualization@lists.linux-foundation.org https://lists.linuxfoundation.org/mailman/listinfo/virtualization
next prev parent reply other threads:[~2020-11-23 15:15 UTC|newest] Thread overview: 107+ messages / expand[flat|nested] mbox.gz Atom feed top 2020-11-20 11:46 [PATCH v2 00/12] x86: major paravirt cleanup Juergen Gross 2020-11-20 11:46 ` Juergen Gross via Virtualization 2020-11-20 11:46 ` [PATCH v2 01/12] x86/xen: use specific Xen pv interrupt entry for MCE Juergen Gross 2020-12-09 21:03 ` Thomas Gleixner 2020-11-20 11:46 ` [PATCH v2 02/12] x86/xen: use specific Xen pv interrupt entry for DF Juergen Gross 2020-12-09 21:03 ` Thomas Gleixner 2020-11-20 11:46 ` [PATCH v2 03/12] x86/pv: switch SWAPGS to ALTERNATIVE Juergen Gross 2020-11-20 11:46 ` Juergen Gross via Virtualization 2020-11-27 11:31 ` Borislav Petkov 2020-11-27 11:31 ` Borislav Petkov 2020-12-09 21:07 ` Thomas Gleixner 2020-12-09 21:07 ` Thomas Gleixner 2020-11-20 11:46 ` [PATCH v2 04/12] x86/xen: drop USERGS_SYSRET64 paravirt call Juergen Gross 2020-11-20 11:46 ` Juergen Gross via Virtualization 2020-12-02 12:32 ` Borislav Petkov 2020-12-02 12:32 ` Borislav Petkov 2020-12-02 14:48 ` Jürgen Groß 2020-12-02 14:48 ` Jürgen Groß via Virtualization 2020-12-02 17:08 ` Borislav Petkov 2020-12-02 17:08 ` Borislav Petkov 2020-11-20 11:46 ` [PATCH v2 05/12] x86: rework arch_local_irq_restore() to not use popf Juergen Gross 2020-11-20 11:46 ` Juergen Gross via Virtualization 2020-11-20 11:59 ` Peter Zijlstra 2020-11-20 11:59 ` Peter Zijlstra 2020-11-20 12:05 ` Jürgen Groß 2020-11-20 12:05 ` Jürgen Groß via Virtualization 2020-11-22 6:55 ` Jürgen Groß 2020-11-22 6:55 ` Jürgen Groß via Virtualization 2020-11-22 21:44 ` Andy Lutomirski 2020-11-22 21:44 ` Andy Lutomirski 2020-11-22 21:44 ` Andy Lutomirski 2020-11-23 5:21 ` Jürgen Groß 2020-11-23 5:21 ` Jürgen Groß via Virtualization 2020-11-23 15:15 ` Andy Lutomirski [this message] 2020-11-23 15:15 ` Andy Lutomirski 2020-12-09 13:27 ` Mark Rutland 2020-12-09 13:27 ` Mark Rutland 2020-12-09 14:02 ` Mark Rutland 2020-12-09 14:02 ` Mark Rutland 2020-12-09 14:05 ` Jürgen Groß 2020-12-09 14:05 ` Jürgen Groß via Virtualization 2020-12-09 18:15 ` Mark Rutland 2020-12-09 18:15 ` Mark Rutland 2020-12-09 18:54 ` Thomas Gleixner 2020-12-09 18:54 ` Thomas Gleixner 2020-12-10 11:10 ` Mark Rutland 2020-12-10 11:10 ` Mark Rutland 2020-12-10 20:15 ` x86/ioapic: Cleanup the timer_works() irqflags mess Thomas Gleixner 2020-12-10 20:15 ` Thomas Gleixner 2020-12-10 22:04 ` [tip: x86/apic] " tip-bot2 for Thomas Gleixner 2020-12-11 5:10 ` Jürgen Groß 2020-12-11 5:10 ` Jürgen Groß via Virtualization 2020-11-27 2:20 ` [x86] 97e8f0134a: fio.write_iops 8.6% improvement kernel test robot 2020-11-20 11:46 ` [PATCH v2 06/12] x86/paravirt: switch time pvops functions to use static_call() Juergen Gross 2020-11-20 11:46 ` Juergen Gross via Virtualization 2020-11-20 12:01 ` Peter Zijlstra 2020-11-20 12:01 ` Peter Zijlstra 2020-11-20 12:07 ` Jürgen Groß 2020-11-20 12:07 ` Jürgen Groß via Virtualization 2020-11-20 11:46 ` [PATCH v2 07/12] x86: add new features for paravirt patching Juergen Gross 2020-12-08 18:43 ` Borislav Petkov 2020-12-09 7:30 ` Jürgen Groß 2020-12-09 12:03 ` Borislav Petkov 2020-12-09 12:22 ` Jürgen Groß 2020-12-10 17:58 ` Borislav Petkov 2020-11-20 11:46 ` [PATCH v2 08/12] x86/paravirt: remove no longer needed 32-bit pvops cruft Juergen Gross 2020-11-20 11:46 ` Juergen Gross via Virtualization 2020-11-20 12:08 ` Peter Zijlstra 2020-11-20 12:08 ` Peter Zijlstra 2020-11-20 12:16 ` Jürgen Groß 2020-11-20 12:16 ` Jürgen Groß via Virtualization 2020-11-20 16:52 ` Arvind Sankar 2020-11-20 11:46 ` [PATCH v2 09/12] x86/paravirt: switch iret pvops to ALTERNATIVE Juergen Gross 2020-11-20 11:46 ` Juergen Gross via Virtualization 2020-11-20 11:46 ` [PATCH v2 10/12] x86/paravirt: add new macros PVOP_ALT* supporting pvops in ALTERNATIVEs Juergen Gross 2020-11-20 11:46 ` Juergen Gross via Virtualization 2020-11-20 11:46 ` [PATCH v2 11/12] x86/paravirt: switch functions with custom code to ALTERNATIVE Juergen Gross 2020-11-20 11:46 ` Juergen Gross via Virtualization 2020-11-20 15:46 ` kernel test robot 2020-11-20 15:46 ` kernel test robot 2020-11-20 15:46 ` kernel test robot 2020-11-25 15:46 ` [x86/paravirt] fd8d46a7a2: kernel-selftests.livepatch.test-callbacks.sh.fail kernel test robot 2020-11-20 11:46 ` [PATCH v2 12/12] x86/paravirt: have only one paravirt patch function Juergen Gross 2020-11-20 11:46 ` Juergen Gross via Virtualization 2020-11-20 14:18 ` kernel test robot 2020-11-20 14:18 ` kernel test robot 2020-11-20 14:18 ` kernel test robot 2020-11-20 12:53 ` [PATCH v2 00/12] x86: major paravirt cleanup Peter Zijlstra 2020-11-20 12:53 ` Peter Zijlstra 2020-11-23 13:43 ` Peter Zijlstra 2020-11-23 13:43 ` Peter Zijlstra 2020-12-15 11:42 ` Jürgen Groß 2020-12-15 11:42 ` Jürgen Groß via Virtualization 2020-12-15 14:18 ` Peter Zijlstra 2020-12-15 14:18 ` Peter Zijlstra 2020-12-15 14:54 ` Peter Zijlstra 2020-12-15 14:54 ` Peter Zijlstra 2020-12-15 15:07 ` Jürgen Groß 2020-12-15 15:07 ` Jürgen Groß via Virtualization 2020-12-16 0:38 ` Josh Poimboeuf 2020-12-16 0:38 ` Josh Poimboeuf 2020-12-16 8:40 ` Peter Zijlstra 2020-12-16 8:40 ` Peter Zijlstra 2020-12-16 16:56 ` Josh Poimboeuf 2020-12-16 16:56 ` Josh Poimboeuf 2020-12-16 17:58 ` Peter Zijlstra 2020-12-16 17:58 ` Peter Zijlstra
Reply instructions: You may reply publicly to this message via plain-text email using any one of the following methods: * Save the following mbox file, import it into your mail client, and reply-to-all from there: mbox Avoid top-posting and favor interleaved quoting: https://en.wikipedia.org/wiki/Posting_style#Interleaved_style * Reply using the --to, --cc, and --in-reply-to switches of git-send-email(1): git send-email \ --in-reply-to=DD12CB44-457E-4FE1-8240-B334B785A93C@amacapital.net \ --to=luto@amacapital.net \ --cc=boris.ostrovsky@oracle.com \ --cc=bp@alien8.de \ --cc=hpa@zytor.com \ --cc=jgross@suse.com \ --cc=linux-kernel@vger.kernel.org \ --cc=luto@kernel.org \ --cc=mingo@redhat.com \ --cc=peterz@infradead.org \ --cc=pv-drivers@vmware.com \ --cc=sstabellini@kernel.org \ --cc=tglx@linutronix.de \ --cc=virtualization@lists.linux-foundation.org \ --cc=x86@kernel.org \ --cc=xen-devel@lists.xenproject.org \ /path/to/YOUR_REPLY https://kernel.org/pub/software/scm/git/docs/git-send-email.html * If your mail client supports setting the In-Reply-To header via mailto: links, try the mailto: linkBe sure your reply has a Subject: header at the top and a blank line before the message body.
This is an external index of several public inboxes, see mirroring instructions on how to clone and mirror all data and code used by this external index.