On 07/18/18 at 03:40pm, AKASHI Takahiro wrote:
> On Wed, Jul 18, 2018 at 02:13:50PM +0800, Dave Young wrote:
> > Hi AKASHI,
> >
> > On 07/18/18 at 02:38pm, AKASHI Takahiro wrote:
> > > Dave,
> > >
> > > On Tue, Jul 17, 2018 at 03:49:23PM +0800, Dave Young wrote:
> > > > Hi AKASHI,
> > > > On 07/17/18 at 02:31pm, AKASHI Takahiro wrote:
> > > > > Hi Dave,
> > > > >
> > > > > On Mon, Jul 16, 2018 at 08:24:12PM +0800, Dave Young wrote:
> > > > > > On 07/16/18 at 12:04pm, James Morse wrote:
> > > > > > > Hi Dave,
> > > > > > >
> > > > > > > On 14/07/18 02:52, Dave Young wrote:
> > > > > > > > On 07/11/18 at 04:41pm, AKASHI Takahiro wrote:
> > > > > > > >> Memblock list is another source for usable system memory
> > > > > > > >> layout.
> > > > > > > >> So powerpc's arch_kexec_walk_mem() is moved to kexec_file.c so
> > > > > > > >> that
> > > > > > > >> other memblock-based architectures, particularly arm64, can
> > > > > > > >> also utilise
> > > > > > > >> it. A moved function is now renamed to kexec_walk_memblock()
> > > > > > > >> and merged
> > > > > > > >> into the existing arch_kexec_walk_mem() for general use,
> > > > > > > >> either resource
> > > > > > > >> list or memblock list.
> > > > > > > >>
> > > > > > > >> A consequent function will not work for kdump with memblock
> > > > > > > >> list, but
> > > > > > > >> this will be fixed in the next patch.
> > > > > > >
> > > > > > > >> diff --git a/kernel/kexec_file.c b/kernel/kexec_file.c
> > > > > > >
> > > > > > > >> @@ -513,6 +563,10 @@ static int
> > > > > > > >> locate_mem_hole_callback(struct resource *res, void *arg)
> > > > > > > >> int __weak arch_kexec_walk_mem(struct kexec_buf *kbuf,
> > > > > > > >> int (*func)(struct resource *,
> > > > > > > >> void *))
> > > > > > > >> {
> > > > > > > >> + if (IS_ENABLED(CONFIG_HAVE_MEMBLOCK) &&
> > > > > > > >> +
> > > > > > > >> !IS_ENABLED(CONFIG_ARCH_DISCARD_MEMBLOCK))
> > > > > > > >> + return kexec_walk_memblock(kbuf, func);
> > > > > > > >
> > > > > > > > AKASHI, I'm not sure if this works on all arches, for example I
> > > > > > > > chekced
> > > > > > > > the .config on my Nokia N900 kernel tree, there is
> > > > > > > > HAVE_MEMBLOCK=y and
> > > > > > > > no CONFIG_ARCH_DISCARD_MEMBLOCK, in 32bit arm code no
> > > > > > > > arch_kexec_walk_mem()
> > > > > > > By doesn't work you mean it's a change in behaviour?
> > > > > > > I think this is fine because 32bit arm doesn't support
> > > > > > > KEXEC_FILE, (this file is
> > > > > > > kexec_file specific right?).
> > > > > >
> > > > > > Ah, replied on a train, I forgot this is only for kexec_file, sorry
> > > > > > about that. Please ignore the comment.
> > > > > >
> > > > > > But since we have a weak function arch_kexec_walk_mem, adding
> > > > > > another
> > > > > > condition branch within this weak function looks not good.
> > > > > > Something like below would be better:
> > > > >
> > > > > I see your concern here, but
> > > > >
> > > > >
> > > > > > int kexec_locate_mem_hole(struct kexec_buf *kbuf)
> > > > > > {
> > > > > > int ret;
> > > > > >
> > > > > > + if use memblock
> > > > > > + ret = kexec_walk_memblock()
> > > > > > + else
> > > > > > ret = arch_kexec_walk_mem(kbuf,
> > > > > > locate_mem_hole_callback);
> > > > > >
> > > > > > return ret == 1 ? 0 : -EADDRNOTAVAIL;
> > > > > > }
> > > > >
> > > > > what if yet another architecture comes to kexec_file and wanna
> > > > > take a third approach? How can it override those functions?
> > > > > Depending on kernel configuration, it might re-define either
> > > > > kexec_walk_memblock() or arch_kexec_walk_mem(). It sounds weird to me.
> > > >
> > > > I also feel this weird, but it is slightly better because currently no
> > > > user need another overriding requirement, and I feel it is not expected
> > > > to have in
> > > > the future for the memblock use.
> > > >
> > > > Rethinking about this issue, we can just remove the weak function and
> > > > just use general function.
> > >
> > > Do you really want to remove "weak" attribute?
> > >
> > > > Currently with your patch applied only s390 use arch_kexec_walk_mem like
> > > > below:
> > > > /*
> > > > * The kernel is loaded to a fixed location. Turn off
> > > > kexec_locate_mem_hole
> > > > * and provide kbuf->mem by hand.
> > > > */
> > > > int arch_kexec_walk_mem(struct kexec_buf *kbuf,
> > > > int (*func)(struct resource *, void *))
> > > > {
> > > > return 1;
> > > > }
> > > >
> > > > AFAIK, all other users initialize kbuf->mem as NULL, so we can check
> > >
> > > As a matter of fact, nobody initializes kbuf->mem before calling
> > > kexec_add_buffer (in turn, kexec_locate_mem_hole()).
> >
> > Not sure we understand each other..
> > Let's take an example in arch/x86/kernel/kexec-bzimage64.c:
> > bzImage64_load() :
> > struct kexec_buf kbuf = { .image = image, .buf_max = ULONG_MAX,
> > .top_down = true };
> >
> > Except the three fields above other members will be initialized as zero
> > when compiling including the kbuf->mem
>
> Ah, you're right.
> (My armr64 patch doesn't use struct initializer, though.)
>
> > >
> > > > kbuf->mem in int kexec_locate_mem_hole:
> > > >
> > > > if (kbuf->mem)
> > > > return 0;
> > > >
> > > > if use memblock
> > > > kexec_walk_memblock
> > > > else
> > > > kexec_walk_mem
> >
> > kexec_walk_resource will be better than kexec_walk_mem
> >
> > >
> > > I think that your solution will work for existing architectures
> > > with appropriate patches, but to take your approach, as I said above,
> > > we will have to modify every call site on all kexec_file-capable
> > > architectures.
> > >
> > > If this is what you expect, I will work on it, but I don't think
> > > that it would be a better idea.
>
> So you would expect me to modify my own arm64 code as well as s390.
Yes :) But I had not get time to read all your patches so I was not
aware the struct initialization in arm64 code so I assumed only s390
need a change..
Thanks
Dave
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