linux-kernel - Re: [PATCH v2] ARM: mm: proc-macros: ensure *_tlb

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Message-ID: <CAKwvOdmOEhbc_LdsBTuFojPXa77DQNkjS7b8EyZzQ6SjRREy9g@mail.gmail.com>
Date:   Wed, 29 Sep 2021 13:59:56 -0700
From:   Nick Desaulniers <ndesaulniers@...gle.com>
To:     Ard Biesheuvel <ardb@...nel.org>
Cc:     Linux ARM <linux-arm-kernel@...ts.infradead.org>,
        Fangrui Song <maskray@...gle.com>,
        Peter Smith <Peter.Smith@....com>,
        Nathan Chancellor <nathan@...nel.org>,
        Richard Henderson <richard.henderson@...aro.org>,
        Russell King <linux@...linux.org.uk>,
        Dave Martin <dave.martin@....com>,
        Nicolas Pitre <nico@...xnic.net>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        llvm@...ts.linux.dev
Subject: Re: [PATCH v2] ARM: mm: proc-macros: ensure *_tlb_fns are 4B aligned

On Wed, Sep 29, 2021 at 1:57 PM Ard Biesheuvel <ardb@...nel.org> wrote:
>
> On Wed, 29 Sept 2021 at 21:20, Nick Desaulniers <ndesaulniers@...gle.com> wrote:
> >
> > QEMU 6.1.0 is more correct about trapping on misaligned accesses.
>
> Btw, this is not entirely relevant. QEMU now behaves like every single
> hardware implementation does, and reports an alignment fault when
> using a load-multiple instruction on an address that is not 32-bit
> aligned, as the architecture requires.

Sure, I can drop that line from the commit message when submitting to
RMK's queue.

>
>
> > A
> > kernel built with CONFIG_THUMB2_KERNEL=y and using clang as the
> > assembler could generate non-naturally-aligned v7wbi_tlb_fns which
> > results in a boot failure. The original commit adding the macro missed
> > the .align directive on this data.
> >
> > Fixes: 66a625a88174 ("ARM: mm: proc-macros: Add generic proc/cache/tlb struct definition macros")
> > Link: https://github.com/ClangBuiltLinux/linux/issues/1447
> > Link: https://lore.kernel.org/all/0699da7b-354f-aecc-a62f-e25693209af4@linaro.org/
> > Debugged-by: Ard Biesheuvel <ardb@...nel.org>
> > Debugged-by: Nathan Chancellor <nathan@...nel.org>
> > Debugged-by: Richard Henderson <richard.henderson@...aro.org>
> > Suggested-by: Ard Biesheuvel <ardb@...nel.org>
> > Acked-by: Ard Biesheuvel <ardb@...nel.org>
> > Signed-off-by: Nick Desaulniers <ndesaulniers@...gle.com>
> > ---
> > Changes V1 -> V2:
> > * Drop accidentally committed Kconfig change.
> > * Pick up Ard's AB tag.
> >
> >  arch/arm/mm/proc-macros.S | 1 +
> >  1 file changed, 1 insertion(+)
> >
> > diff --git a/arch/arm/mm/proc-macros.S b/arch/arm/mm/proc-macros.S
> > index e2c743aa2eb2..d9f7dfe2a7ed 100644
> > --- a/arch/arm/mm/proc-macros.S
> > +++ b/arch/arm/mm/proc-macros.S
> > @@ -340,6 +340,7 @@ ENTRY(\name\()_cache_fns)
> >
> >  .macro define_tlb_functions name:req, flags_up:req, flags_smp
> >         .type   \name\()_tlb_fns, #object
> > +       .align 2
> >  ENTRY(\name\()_tlb_fns)
> >         .long   \name\()_flush_user_tlb_range
> >         .long   \name\()_flush_kern_tlb_range
> >
> > base-commit: 02d5e016800d082058b3d3b7c3ede136cdc6ddcb
> > prerequisite-patch-id: 3edbe4a8485c7a75a61dbbe299e8ce1985d87ee0
> > --
> > 2.33.0.685.g46640cef36-goog
> >



-- 
Thanks,
~Nick Desaulniers