On Wed, 29 May 2013 12:23:26 -0400 Vivek Goyal <vgoyal at redhat.com> wrote: > On Wed, May 29, 2013 at 01:51:44PM +0200, Michael Holzheu wrote: > > On Tue, 28 May 2013 09:55:01 -0400 > > Vivek Goyal <vgoyal at redhat.com> wrote: > > > > > On Sat, May 25, 2013 at 02:52:17PM +0200, Michael Holzheu wrote: > > > > [snip] > > > > > > Besides of the newmem mechanism, for completeness, we also > > > > implemented the oldmem ELF header mechansim in kexec. But this > > > > is disabled by default. > > > > > > > > See: "#ifdef WITH_ELF_HEADER" in > > > > kexec/arch/s390/crashdump-s390.c > > > > > > > > Currently no distribution uses the oldmem mechanism. > > > > > > Hi Michael, > > > > > > Mechanism to read from newmem is not there yet (your patches are > > > still being reviewed) and you mentioned that no distribution is > > > building kexec-tools with WITH_ELF_HEADER on s390. So how things > > > are currently working for kdump on s390? > > > > Hello Vivek, > > > > On s390, if we do not get the ELF header from the 1st kernel with > > "elfcorehdr=", we build the ELF header in the 2nd kernel. This is > > currently the default because WITH_ELF_HEADER is not defined for > > kexec tools. > > > > >>> START QUOTE > > > > [PATCH v3 1/3] kdump: Introduce ELF header in new memory feature > > > > Currently for s390 we create the ELF core header in the 2nd kernel > > with a small trick. We relocate the addresses in the ELF header in > > a way that for the /proc/vmcore code it seems to be in the 1st > > kernel (old) memory and the read_from_oldmem() returns the correct > > data. This allows the /proc/vmcore code to use the ELF header in > > the 2nd kernel. > > > > >>> END QUOTE > > > > For our current zfcpdump project (see "[PATCH 3/3]s390/kdump: Use > > vmcore for zfcpdump") we could no longer use this trick. Therefore > > we sent you the patches to get a clean interface for ELF header > > creation in the 2nd kernel. > > > > > > > > > > Therefore, if necessary, IMHO we can switch to the ELF header > > > > memory swap mechanism for s390 in the kernel. Of course we > > > > would then also have to adjust the (disabled) kexec code. > > > > > > So are you saying that s390 is ready to switch to mechanism of > > > creating ELF headers in first kernel by kexec-tools and new kernel > > > does not have to preare ELF headers? > > > > No, I meant that currently nobody is using the kexec tools ELF > > header creation in the 1st kernel on s390. We create the ELF header > > in the 2nd kernel (mainly because of our cpuplugd issue). > > > > Therefore, I think, we can safely change the ELF header creation in > > 2nd kernel to use your p_offset swap trick *and* we remove the swap > > code in the copy_oldmem_page() implementation (same kernel). > > Ok. Got it. So s390 can fix it in kernel without creating any backward > compatibility issues (given the fact that nobody sees to be using > kexec-tools to build headers). > > So please go ahead and fix it and that should solve your mmap() issue > too. Also please fix kexec-tools and that change will not be backward > compatible. Ok, I will do this. I think we should add this "swap in ELF header" patch to the "kdump: Allow ELF header creation in new kernel" patch series (on top of the mmap patch series). Because when I remove the swap code from copy_oldmem_page(), the old trick to access the ELF header in the first kernel memory will no longer work. Is that ok for you? Michael
