Messages in this thread | | | Date | Mon, 6 Aug 2018 13:50:47 +0800 | From | Dave Young <> | Subject | Re: [PATCH v13 03/16] s390, kexec_file: drop arch_kexec_mem_walk() |
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Add Thiago in cc so that he can review from powerpc point of view.
On 08/02/18 at 09:01am, AKASHI Takahiro wrote: > Hi, > > On Wed, Aug 01, 2018 at 10:29:51AM +0200, Philipp Rudo wrote: > > Hey Akashi, > > > > I kept thinking about this patch and remembered why I didn't made the change > > you are suggesting now. > > Hmm. > > > The problem is when you only check for kbuf->mem you are excluding address 0, > > which might be a valid address to load the kernel to. On s390 this is actually > > done when the kernel is not loaded via a boot loader. For kexec_file however, > > we cut off the first few kB of the image and jump directly to 'startup'. So > > checking for !0 does not cause a problem here. > > Yeah, as Dave(RedHat) described, all the current kexec-capable architectures, > except arm64, implicitly initialize kbuf.mem to zero with "kbuf = { ... }" > initializer. So surely my change would not break anything on the existing code. > On the other hand, I also see your concern here. > > > Anyway, the long term safer solution would be something like > > > > #define KEXEC_BUF_MEM_UNKNOWN (-1UL) > > > > for architectures to tell common code to search a fitting mem hole. > > This would require the existing code on every arch to be modified, which > I think should be avoided if possible. Instead, > we'd better define in linux/kexec.h: > #ifndef KEXEC_BUF_MEM_UNKNOWN > #define KEXEC_BUF_MEM_UNKNOWN 0 > #endif > and then check for kbuf in kexec_locate_mem_hole(): > if (kbuf->mem != KEXEC_BUF_MEM_UNKNOWN) > return 0; > ... > > This way if some arch wants to treat *zero* as a valid address, it can > redefine this macro in arch/asm/kexec.h.
I think this way works if powerpc is safe for using zero as the unknown address in this case. Thiago, can you provide some review?
Philipp, thanks for catching the problem!
> > Thanks, > -Takahiro AKASHI > > > > > Back then I didn't do the change because I had the other workaround, which > > didn't require a common code change. But when you are touching the code now it > > is worth thinking about it. > > > > Just wanted to let you know > > Philipp > > > > > > On Wed, 1 Aug 2018 16:58:07 +0900 > > AKASHI Takahiro <takahiro.akashi@linaro.org> wrote: > > > > > Since s390 already knows where to locate buffers, calling > > > arch_kexec_mem_walk() has no sense. So we can just drop it as kbuf->mem > > > indicates this while all other architectures sets it to 0 initially. > > > > > > This change is a preparatory work for the next patch, where all the > > > variant memory walks, either on system resource or memblock, will be > > > put in one common place so that it will satisfy all the architectures' > > > need. > > > > > > Signed-off-by: AKASHI Takahiro <takahiro.akashi@linaro.org> > > > Reviewed-by: Philipp Rudo <prudo@linux.ibm.com> > > > Cc: Martin Schwidefsky <schwidefsky@de.ibm.com> > > > Cc: Heiko Carstens <heiko.carstens@de.ibm.com> > > > Cc: Dave Young <dyoung@redhat.com> > > > Cc: Vivek Goyal <vgoyal@redhat.com> > > > Cc: Baoquan He <bhe@redhat.com> > > > --- > > > arch/s390/kernel/machine_kexec_file.c | 10 ---------- > > > kernel/kexec_file.c | 4 ++++ > > > 2 files changed, 4 insertions(+), 10 deletions(-) > > > > > > diff --git a/arch/s390/kernel/machine_kexec_file.c b/arch/s390/kernel/machine_kexec_file.c > > > index f413f57f8d20..32023b4f9dc0 100644 > > > --- a/arch/s390/kernel/machine_kexec_file.c > > > +++ b/arch/s390/kernel/machine_kexec_file.c > > > @@ -134,16 +134,6 @@ int kexec_file_add_initrd(struct kimage *image, struct s390_load_data *data, > > > return ret; > > > } > > > > > > -/* > > > - * 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; > > > -} > > > - > > > int arch_kexec_apply_relocations_add(struct purgatory_info *pi, > > > Elf_Shdr *section, > > > const Elf_Shdr *relsec, > > > diff --git a/kernel/kexec_file.c b/kernel/kexec_file.c > > > index 63c7ce1c0c3e..bf39df5e5bb9 100644 > > > --- a/kernel/kexec_file.c > > > +++ b/kernel/kexec_file.c > > > @@ -534,6 +534,10 @@ int kexec_locate_mem_hole(struct kexec_buf *kbuf) > > > { > > > int ret; > > > > > > + /* Arch knows where to place */ > > > + if (kbuf->mem) > > > + return 0; > > > + > > > ret = arch_kexec_walk_mem(kbuf, locate_mem_hole_callback); > > > > > > return ret == 1 ? 0 : -EADDRNOTAVAIL; > > > > _______________________________________________ > kexec mailing list > kexec@lists.infradead.org > http://lists.infradead.org/mailman/listinfo/kexec
Thanks Dave
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