linux-kernel - Re: [PATCH v3 18/26] arm64: Introduce asm/vdso/processor.h

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Message-ID: <20200316102621.GC3005@mbp>
Date:   Mon, 16 Mar 2020 10:26:22 +0000
From:   Catalin Marinas <catalin.marinas@....com>
To:     Mark Rutland <mark.rutland@....com>
Cc:     Vincenzo Frascino <vincenzo.frascino@....com>,
        linux-arch@...r.kernel.org, linux-arm-kernel@...ts.infradead.org,
        linux-kernel@...r.kernel.org, linux-mips@...r.kernel.org,
        clang-built-linux@...glegroups.com, x86@...nel.org,
        Will Deacon <will.deacon@....com>,
        Arnd Bergmann <arnd@...db.de>,
        Russell King <linux@...linux.org.uk>,
        Paul Burton <paul.burton@...s.com>,
        Thomas Gleixner <tglx@...utronix.de>,
        Andy Lutomirski <luto@...nel.org>,
        Ingo Molnar <mingo@...hat.com>, Borislav Petkov <bp@...en8.de>,
        Stephen Boyd <sboyd@...nel.org>,
        Mark Salyzyn <salyzyn@...roid.com>,
        Kees Cook <keescook@...omium.org>,
        Peter Collingbourne <pcc@...gle.com>,
        Dmitry Safonov <0x7f454c46@...il.com>,
        Andrei Vagin <avagin@...nvz.org>,
        Nick Desaulniers <ndesaulniers@...gle.com>,
        Marc Zyngier <maz@...nel.org>, Will Deacon <will@...nel.org>
Subject: Re: [PATCH v3 18/26] arm64: Introduce asm/vdso/processor.h

On Mon, Mar 16, 2020 at 10:22:15AM +0000, Mark Rutland wrote:
> On Mon, Mar 16, 2020 at 09:42:32AM +0000, Vincenzo Frascino wrote:
> > On 3/15/20 6:30 PM, Catalin Marinas wrote:
> > > On Fri, Mar 13, 2020 at 03:43:37PM +0000, Vincenzo Frascino wrote:
> > >> --- /dev/null
> > >> +++ b/arch/arm64/include/asm/vdso/processor.h
> > >> @@ -0,0 +1,31 @@
> > >> +/* SPDX-License-Identifier: GPL-2.0-only */
> > >> +/*
> > >> + * Copyright (C) 2020 ARM Ltd.
> > >> + */
> > >> +#ifndef __ASM_VDSO_PROCESSOR_H
> > >> +#define __ASM_VDSO_PROCESSOR_H
> > >> +
> > >> +#ifndef __ASSEMBLY__
> > >> +
> > >> +#include <asm/page-def.h>
> > >> +
> > >> +#ifdef CONFIG_COMPAT
> > >> +#if defined(CONFIG_ARM64_64K_PAGES) && defined(CONFIG_KUSER_HELPERS)
> > >> +/*
> > >> + * With CONFIG_ARM64_64K_PAGES enabled, the last page is occupied
> > >> + * by the compat vectors page.
> > >> + */
> > >> +#define TASK_SIZE_32		UL(0x100000000)
> > >> +#else
> > >> +#define TASK_SIZE_32		(UL(0x100000000) - PAGE_SIZE)
> > >> +#endif /* CONFIG_ARM64_64K_PAGES */
> > >> +#endif /* CONFIG_COMPAT */
> > > 
> > > Just curious, what's TASK_SIZE_32 used for in the vDSO code? You don't
> > > seem to move TASK_SIZE.
> > > 
> > 
> > I tried to fine grain the headers as much as I could in order to avoid
> > unneeded/unwanted inclusions:
> >  * TASK_SIZE_32 is used to verify ABI consistency on vdso32 (please refer to
> >    arch/arm64/kernel/vdso32/vgettimeofday.c).
> >  * TASK_SIZE is not required by the vdso library hence it is not present in
> >    these headers.
> 
> It would be worth noting the former point in the commit message, since
> it can be surprising.
> 
> I also think it's worth keeping the definitions together if that's easy,
> as it makes it easier to navigate the codebase, even if TASK_SIZE isn't
> necessary for the VDSO itself.

It won't work as TASK_SIZE requires (on arm64) test_thread_flag() which
can't be made available to the vDSO.

-- 
Catalin