linux-kernel - Re: [PATCH v7 07/10] kernel/jump_label: abstract jump

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Date:   Fri, 5 Jan 2018 18:22:29 +0000
From:   Catalin Marinas <catalin.marinas@....com>
To:     Ard Biesheuvel <ard.biesheuvel@...aro.org>
Cc:     linux-mips <linux-mips@...ux-mips.org>,
        Benjamin Herrenschmidt <benh@...nel.crashing.org>,
        Will Deacon <will.deacon@....com>,
        Paul Mackerras <paulus@...ba.org>,
        "H. Peter Anvin" <hpa@...or.com>, sparclinux@...r.kernel.org,
        linux-s390 <linux-s390@...r.kernel.org>,
        Nicolas Pitre <nico@...aro.org>,
        Michael Ellerman <mpe@...erman.id.au>,
        the arch/x86 maintainers <x86@...nel.org>,
        Russell King <linux@...linux.org.uk>,
        Ingo Molnar <mingo@...hat.com>,
        "Serge E. Hallyn" <serge@...lyn.com>,
        Petr Mladek <pmladek@...e.com>,
        Kees Cook <keescook@...omium.org>,
        Arnd Bergmann <arnd@...db.de>,
        Heiko Carstens <heiko.carstens@...ibm.com>,
        Steven Rostedt <rostedt@...dmis.org>,
        James Morris <james.l.morris@...cle.com>,
        Josh Poimboeuf <jpoimboe@...hat.com>,
        Bjorn Helgaas <bhelgaas@...gle.com>,
        Thomas Gleixner <tglx@...utronix.de>,
        linux-arm-kernel@...ts.infradead.org,
        Linus Torvalds <torvalds@...ux-foundation.org>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        Ralf Baechle <ralf@...ux-mips.org>,
        "David S. Miller" <davem@...emloft.net>,
        Sergey Senozhatsky <sergey.senozhatsky@...il.com>,
        Jessica Yu <jeyu@...nel.org>,
        Martin Schwidefsky <schwidefsky@...ibm.com>,
        Andrew Morton <akpm@...ux-foundation.org>,
        linuxppc-dev <linuxppc-dev@...ts.ozlabs.org>,
        Thomas Garnier <thgarnie@...gle.com>
Subject: Re: [PATCH v7 07/10] kernel/jump_label: abstract jump_entry member
 accessors

On Fri, Jan 05, 2018 at 06:01:33PM +0000, Ard Biesheuvel wrote:
> On 5 January 2018 at 17:58, Catalin Marinas <catalin.marinas@....com> wrote:
> > On Tue, Jan 02, 2018 at 08:05:46PM +0000, Ard Biesheuvel wrote:
> >> diff --git a/arch/arm/include/asm/jump_label.h b/arch/arm/include/asm/jump_label.h
> >> index e12d7d096fc0..7b05b404063a 100644
> >> --- a/arch/arm/include/asm/jump_label.h
> >> +++ b/arch/arm/include/asm/jump_label.h
> >> @@ -45,5 +45,32 @@ struct jump_entry {
> >>       jump_label_t key;
> >>  };
> >>
> >> +static inline jump_label_t jump_entry_code(const struct jump_entry *entry)
> >> +{
> >> +     return entry->code;
> >> +}
> >> +
> >> +static inline struct static_key *jump_entry_key(const struct jump_entry *entry)
> >> +{
> >> +     return (struct static_key *)((unsigned long)entry->key & ~1UL);
> >> +}
> >> +
> >> +static inline bool jump_entry_is_branch(const struct jump_entry *entry)
> >> +{
> >> +     return (unsigned long)entry->key & 1UL;
> >> +}
> >> +
> >> +static inline bool jump_entry_is_module_init(const struct jump_entry *entry)
> >> +{
> >> +     return entry->code == 0;
> >> +}
> >> +
> >> +static inline void jump_entry_set_module_init(struct jump_entry *entry)
> >> +{
> >> +     entry->code = 0;
> >> +}
> >> +
> >> +#define jump_label_swap              NULL
> >
> > Is there any difference between these functions on any of the
> > architectures touched? Even with the relative offset, arm64 and x86
> > looked the same to me (well, I may have missed some detail).
> 
> No, the latter two are identical everywhere, and the others are the
> same modulo absolute vs relative.
> 
> The issue is that the struct definition is per-arch so the accessors
> should be as well.

Up to this patch, even the jump_entry structure is the same on all
architectures (the jump_label_t type differs).

With relative offset, can you not just define jump_label_t to s32? At a
quick grep in mainline, it doesn't seem to be used outside the structure
definition.

> Perhaps I should introduce two variants two asm-generic, similar to
> how we have different flavors of unaligned accessors.

You could as well define them directly in kernel/jump_label.h or, if
used outside this file, include/linux/jump_label.h.

-- 
Catalin