linux-kernel - Re: [PATCH v10 03/14] powerpc, kexec_file: factor out memblock-based arch_kexec_walk

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Date:   Mon, 9 Jul 2018 14:49:54 +0900
From:   AKASHI Takahiro <takahiro.akashi@...aro.org>
To:     James Morse <james.morse@....com>
Cc:     catalin.marinas@....com, will.deacon@....com, dhowells@...hat.com,
        vgoyal@...hat.com, herbert@...dor.apana.org.au,
        davem@...emloft.net, dyoung@...hat.com, bhe@...hat.com,
        arnd@...db.de, ard.biesheuvel@...aro.org, bhsharma@...hat.com,
        kexec@...ts.infradead.org, linux-arm-kernel@...ts.infradead.org,
        linux-kernel@...r.kernel.org,
        "Eric W. Biederman" <ebiederm@...ssion.com>
Subject: Re: [PATCH v10 03/14] powerpc, kexec_file: factor out memblock-based
 arch_kexec_walk_mem()

James,

On Tue, Jul 03, 2018 at 05:36:24PM +0100, James Morse wrote:
> Hi Akashi,
> 
> On 23/06/18 03:20, AKASHI Takahiro wrote:
> > Memblock list is another source for usable system memory layout.
> > A merged new arch_kexec_walk_mem() will walk through either io resource
> > list or memblock list depending on CONFIG_ARCH_DISCARD_MEMBLOCK so that
> > arm64, in addition to powerpc, will be able to utilize this generic
> > function for kexec_file.
> 
> > diff --git a/arch/powerpc/kernel/machine_kexec_file_64.c b/arch/powerpc/kernel/machine_kexec_file_64.c
> > index 0bd23dc789a4..3d4be91786ce 100644
> > --- a/arch/powerpc/kernel/machine_kexec_file_64.c
> > +++ b/arch/powerpc/kernel/machine_kexec_file_64.c
> 
> Does this file still need its memblock.h include?

OK. Will remove it.

> 
> > diff --git a/kernel/kexec_file.c b/kernel/kexec_file.c
> > index 63c7ce1c0c3e..563acd1c9a61 100644
> > --- a/kernel/kexec_file.c
> > +++ b/kernel/kexec_file.c
> > @@ -16,6 +16,7 @@
> >  #include <linux/file.h>
> >  #include <linux/slab.h>
> >  #include <linux/kexec.h>
> > +#include <linux/memblock.h>
> >  #include <linux/mutex.h>
> >  #include <linux/list.h>
> >  #include <linux/fs.h>
> > @@ -501,6 +502,53 @@ static int locate_mem_hole_callback(struct resource *res, void *arg)
> >  	return locate_mem_hole_bottom_up(start, end, kbuf);
> >  }
> >  
> > +#if defined(CONFIG_HAVE_MEMBLOCK) && !defined(CONFIG_ARCH_DISCARD_MEMBLOCK)
> 
> The only caller is also guarded by these same ifdefs. Can't we remove this and
> rely on the compilers dead-code elimination to remove this function when its not
> needed?

I don't think we can remove this #ifdef.
"for_each_free_mem_range[_reverse]()" is defined under CONFIG_HAVE_MEMBLOCK
in memblock.h. If some architecture wants to support KEXEC_FILE but
doesn't have HAVE_MEMBLOCK, compiling kexec_file.c will fail.

> 
> > +static int kexec_walk_memblock(struct kexec_buf *kbuf,
> > +			       int (*func)(struct resource *, void *))
> > +{
> > +	u64 i;
> > +	phys_addr_t mstart, mend;
> > +	struct resource res = { };
> > +	int ret = 0;
> 
> 
> Keeping this patch as 'just' moving code would avoid having to play
> spot-the-difference:

OK. I will split this patch into two.
But just "moving" is impossible because the function names will be
duplicated in kexec_file.c.

> > +	if (kbuf->image->type == KEXEC_TYPE_CRASH)
> > +		return func(&crashk_res, kbuf);
> 
> This will be new for powerpc, but any attempt to use it should be caught by
> arch_kexec_kernel_image_probe(), which has:
> |	/* We don't support crash kernels yet. */
> |	if (image->type == KEXEC_TYPE_CRASH)
> |		return -EOPNOTSUPP;
> 
> 
> Looks good to me! For what its worth:
> Acked-by: James Morse <james.morse@....com>

Thank you for your reviews.

-Takahiro AKASHI

> 
> Thanks,
> 
> James