On Fri, Aug 30, 2019 at 3:04 PM Donald Buczek <buczek@xxxxxxxxxxxxx> wrote:
>
> Dear Baoquan,
>
> On 8/30/19 11:23 AM, Baoquan He wrote:
> > On 08/30/19 at 11:12am, Donald Buczek wrote:
> >> Linux kernel commit d52888aa2753 ("x86/mm: Move LDT remap out of KASLR
> >> region on 5-level paging") changed the base of the direct mapping
> >> from 0xffff880000000000 to 0xffff888000000000. This was merged
> >> into v4.20-rc2.
> >
> > A good catch and necessary fix, thanks.
> >
> > Does it have issue in makedumpfile?
>
> We don't use makedumpfile. We use `cp /proc/vmcore /mnt/crash.vmcore` in the panic kernel.
That shouldn't be a problem in makedumpfile as we have a generic way
to calculate the PAGE_OFFSET value there from the PT_LOADs in the
'/proc/kcore' file (which I mentioned in the other email conversation,
see [0]):
static int
get_page_offset_x86_64(void)
{
<..snip..>
if (get_num_pt_loads()) {
/*
* Linux 4.19 (only) adds KCORE_REMAP PT_LOADs, which have
* virt_start < __START_KERNEL_map, to /proc/kcore. In order
* not to select them, we select the last valid PT_LOAD.
*/
for (i = 0;
get_pt_load(i, &phys_start, NULL, &virt_start, NULL);
i++) {
if (virt_start != NOT_KV_ADDR
&& virt_start < __START_KERNEL_map
&& phys_start != NOT_PADDR) {
page_offset = virt_start - phys_start;
}
}
if (page_offset) {
info->page_offset = page_offset;
DEBUG_MSG("page_offset : %lx (pt_load)\n",
info->page_offset);
return TRUE;
}
}
<..snip..>
Also as I mentioned in the other thread, I don't think adding
different MACRO value for a kernel version is a long-term maintainable
approach. Instead I am working on adding a similar functionality as
present in makedumpfile to make the PAGE_OFFSET calculation generic.
Only if we fail to calculate PAGE_OFFSET through a generic method
should we fall back on MACRO values for backward compatibility.
I will try to post the patch for reviews by tomorrow.
[0]. https://lkml.org/lkml/2019/8/28/1060
Thanks,
Bhupesh
> Without this patch, the file /mnt/crash.vmcore has the wrong vaddr in the elf headers and can't be processed by gdb or crash.
>
> With this patch, the file has the correct vaddr an can be processed by gdb and crash.
>
> Btw: I've got four strange error replies for my mail.
>
> Date: 30 Aug 2019 05:13:31 EDT
> From: MAILER_DAEMON@xxxxxxxxxxxxxx
> To: buczek@xxxxxxxxxxxxx
> Message to 7867650283@xxxxxxxxxxxxxx failed.
>
> I hope, my patch reaches the right people anyway.
>
> Best
> Donald
>
>
> >
> > #ifdef __x86_64__
> > #define __PAGE_OFFSET_ORIG (0xffff810000000000) /* 2.6.26, or former */
> > #define __PAGE_OFFSET_2_6_27 (0xffff880000000000) /* 2.6.27, or later */
> > #define __PAGE_OFFSET_5LEVEL (0xff10000000000000) /* 5-level page table */
> > ...
> > #endif
> >
> > Thanks
> > Baoquan
> >
> >>
> >> Update to new address accordingly.
> >> ---
> >> kexec/arch/i386/crashdump-x86.c | 2 ++
> >> kexec/arch/i386/crashdump-x86.h | 3 ++-
> >> 2 files changed, 4 insertions(+), 1 deletion(-)
> >>
> >> diff --git a/kexec/arch/i386/crashdump-x86.c b/kexec/arch/i386/crashdump-x86.c
> >> index a2aea31..c79791f 100644
> >> --- a/kexec/arch/i386/crashdump-x86.c
> >> +++ b/kexec/arch/i386/crashdump-x86.c
> >> @@ -61,6 +61,8 @@ static int get_kernel_page_offset(struct kexec_info *UNUSED(info),
> >>
> >> if (kv < KERNEL_VERSION(2, 6, 27))
> >> elf_info->page_offset = X86_64_PAGE_OFFSET_PRE_2_6_27;
> >> + else if (kv < KERNEL_VERSION(4, 20, 0))
> >> + elf_info->page_offset = X86_64_PAGE_OFFSET_PRE_4_20_0;
> >> else
> >> elf_info->page_offset = X86_64_PAGE_OFFSET;
> >> }
> >> diff --git a/kexec/arch/i386/crashdump-x86.h b/kexec/arch/i386/crashdump-x86.h
> >> index ddee19f..e4fdc82 100644
> >> --- a/kexec/arch/i386/crashdump-x86.h
> >> +++ b/kexec/arch/i386/crashdump-x86.h
> >> @@ -13,7 +13,8 @@ int load_crashdump_segments(struct kexec_info *info, char *mod_cmdline,
> >>
> >> #define X86_64__START_KERNEL_map 0xffffffff80000000ULL
> >> #define X86_64_PAGE_OFFSET_PRE_2_6_27 0xffff810000000000ULL
> >> -#define X86_64_PAGE_OFFSET 0xffff880000000000ULL
> >> +#define X86_64_PAGE_OFFSET_PRE_4_20_0 0xffff880000000000ULL
> >> +#define X86_64_PAGE_OFFSET 0xffff888000000000ULL
> >>
> >> #define X86_64_MAXMEM 0x3fffffffffffUL
> >>
> >> --
> >> 2.22.0
> >>
> >>
> >> _______________________________________________
> >> kexec mailing list
> >> kexec@xxxxxxxxxxxxxxxxxxx
> >> http://lists.infradead.org/mailman/listinfo/kexec
>
>
> --
> Donald Buczek
> buczek@xxxxxxxxxxxxx
> Tel: +49 30 8413 1433
_______________________________________________
kexec mailing list
kexec@xxxxxxxxxxxxxxxxxxx
http://lists.infradead.org/mailman/listinfo/kexec
