linux-kernel - Re: [PATCH v2 06/12] mm/execmem: introduce execmem_data

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Message-ID: <20230617065111.GR52412@kernel.org>
Date:   Sat, 17 Jun 2023 09:51:11 +0300
From:   Mike Rapoport <rppt@...nel.org>
To:     Song Liu <song@...nel.org>
Cc:     linux-kernel@...r.kernel.org,
        Andrew Morton <akpm@...ux-foundation.org>,
        Catalin Marinas <catalin.marinas@....com>,
        Christophe Leroy <christophe.leroy@...roup.eu>,
        "David S. Miller" <davem@...emloft.net>,
        Dinh Nguyen <dinguyen@...nel.org>,
        Heiko Carstens <hca@...ux.ibm.com>,
        Helge Deller <deller@....de>,
        Huacai Chen <chenhuacai@...nel.org>,
        Kent Overstreet <kent.overstreet@...ux.dev>,
        Luis Chamberlain <mcgrof@...nel.org>,
        Mark Rutland <mark.rutland@....com>,
        Michael Ellerman <mpe@...erman.id.au>,
        Nadav Amit <nadav.amit@...il.com>,
        "Naveen N. Rao" <naveen.n.rao@...ux.ibm.com>,
        Palmer Dabbelt <palmer@...belt.com>,
        Puranjay Mohan <puranjay12@...il.com>,
        Rick Edgecombe <rick.p.edgecombe@...el.com>,
        Russell King <linux@...linux.org.uk>,
        Steven Rostedt <rostedt@...dmis.org>,
        Thomas Bogendoerfer <tsbogend@...ha.franken.de>,
        Thomas Gleixner <tglx@...utronix.de>,
        Will Deacon <will@...nel.org>, bpf@...r.kernel.org,
        linux-arm-kernel@...ts.infradead.org, linux-mips@...r.kernel.org,
        linux-mm@...ck.org, linux-modules@...r.kernel.org,
        linux-parisc@...r.kernel.org, linux-riscv@...ts.infradead.org,
        linux-s390@...r.kernel.org, linux-trace-kernel@...r.kernel.org,
        linuxppc-dev@...ts.ozlabs.org, loongarch@...ts.linux.dev,
        netdev@...r.kernel.org, sparclinux@...r.kernel.org, x86@...nel.org
Subject: Re: [PATCH v2 06/12] mm/execmem: introduce execmem_data_alloc()

On Fri, Jun 16, 2023 at 01:01:08PM -0700, Song Liu wrote:
> On Fri, Jun 16, 2023 at 1:51 AM Mike Rapoport <rppt@...nel.org> wrote:
> >
> > From: "Mike Rapoport (IBM)" <rppt@...nel.org>
> >
> > Data related to code allocations, such as module data section, need to
> > comply with architecture constraints for its placement and its
> > allocation right now was done using execmem_text_alloc().
> >
> > Create a dedicated API for allocating data related to code allocations
> > and allow architectures to define address ranges for data allocations.
> >
> > Since currently this is only relevant for powerpc variants that use the
> > VMALLOC address space for module data allocations, automatically reuse
> > address ranges defined for text unless address range for data is
> > explicitly defined by an architecture.
> >
> > With separation of code and data allocations, data sections of the
> > modules are now mapped as PAGE_KERNEL rather than PAGE_KERNEL_EXEC which
> > was a default on many architectures.
> >
> > Signed-off-by: Mike Rapoport (IBM) <rppt@...nel.org>
> [...]
> >  static void free_mod_mem(struct module *mod)
> > diff --git a/mm/execmem.c b/mm/execmem.c
> > index a67acd75ffef..f7bf496ad4c3 100644
> > --- a/mm/execmem.c
> > +++ b/mm/execmem.c
> > @@ -63,6 +63,20 @@ void *execmem_text_alloc(size_t size)
> >                              fallback_start, fallback_end, kasan);
> >  }
> >
> > +void *execmem_data_alloc(size_t size)
> > +{
> > +       unsigned long start = execmem_params.modules.data.start;
> > +       unsigned long end = execmem_params.modules.data.end;
> > +       pgprot_t pgprot = execmem_params.modules.data.pgprot;
> > +       unsigned int align = execmem_params.modules.data.alignment;
> > +       unsigned long fallback_start = execmem_params.modules.data.fallback_start;
> > +       unsigned long fallback_end = execmem_params.modules.data.fallback_end;
> > +       bool kasan = execmem_params.modules.flags & EXECMEM_KASAN_SHADOW;
> > +
> > +       return execmem_alloc(size, start, end, align, pgprot,
> > +                            fallback_start, fallback_end, kasan);
> > +}
> > +
> >  void execmem_free(void *ptr)
> >  {
> >         /*
> > @@ -101,6 +115,28 @@ static bool execmem_validate_params(struct execmem_params *p)
> >         return true;
> >  }
> >
> > +static void execmem_init_missing(struct execmem_params *p)
> 
> Shall we call this execmem_default_init_data?

This also fills in jit.text (next patch), so _data doesn't work here :)
And it's not really a default, the defaults are set explicitly for arches
that don't have execmem_arch_params.
 
> > +{
> > +       struct execmem_modules_range *m = &p->modules;
> > +
> > +       if (!pgprot_val(execmem_params.modules.data.pgprot))
> > +               execmem_params.modules.data.pgprot = PAGE_KERNEL;
> 
> Do we really need to check each of these? IOW, can we do:
> 
> if (!pgprot_val(execmem_params.modules.data.pgprot)) {
>        execmem_params.modules.data.pgprot = PAGE_KERNEL;
>        execmem_params.modules.data.alignment = m->text.alignment;
>        execmem_params.modules.data.start = m->text.start;
>        execmem_params.modules.data.end = m->text.end;
>        execmem_params.modules.data.fallback_start = m->text.fallback_start;
>       execmem_params.modules.data.fallback_end = m->text.fallback_end;
> }

Yes, we can have a single check here.
 
> Thanks,
> Song
> 
> [...]

-- 
Sincerely yours,
Mike.