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SubjectRe: [PATCH v4 2/3] x86/kexec/64: Error out if try to jump to old 4-level kernel from 5-level kernel
On 05/22/19 at 11:20am, Dave Young wrote:
> How about the userspace kexec-tools? It needs a similar detection, but
> I'm not sure how to detect paging mode, maybe some sysfs entry or
> vmcoreinfo in /proc/vmcore

In usersapce, I plan to parse /proc/kcore to get the starting address
of page_offset or vmalloc. You can see the different level has different
value range.

4-level:
ffff888000000000 | -119.5 TB | ffffc87fffffffff | 64 TB | direct mapping of all physical memory (page_offset_base)
ffffc88000000000 | -55.5 TB | ffffc8ffffffffff | 0.5 TB | ... unused hole
ffffc90000000000 | -55 TB | ffffe8ffffffffff | 32 TB | vmalloc/ioremap space (vmalloc_base)
ffffe90000000000 | -23 TB | ffffe9ffffffffff | 1 TB | ... unused hole
ffffea0000000000 | -22 TB | ffffeaffffffffff | 1 TB | virtual memory map (vmemmap_base)


5-level:
ff11000000000000 | -59.75 PB | ff90ffffffffffff | 32 PB | direct mapping of all physical memory (page_offset_base)
ff91000000000000 | -27.75 PB | ff9fffffffffffff | 3.75 PB | ... unused hole
ffa0000000000000 | -24 PB | ffd1ffffffffffff | 12.5 PB | vmalloc/ioremap space (vmalloc_base)
ffd2000000000000 | -11.5 PB | ffd3ffffffffffff | 0.5 PB | ... unused hole
ffd4000000000000 | -11 PB | ffd5ffffffffffff | 0.5 PB | virtual memory map (vmemmap_base)
>
>
> > 1 file changed, 5 insertions(+)
> >
> > diff --git a/arch/x86/kernel/kexec-bzimage64.c b/arch/x86/kernel/kexec-bzimage64.c
> > index 22f60dd26460..858cc892672f 100644
> > --- a/arch/x86/kernel/kexec-bzimage64.c
> > +++ b/arch/x86/kernel/kexec-bzimage64.c
> > @@ -321,6 +321,11 @@ static int bzImage64_probe(const char *buf, unsigned long len)
> > return ret;
> > }
> >
> > + if (!(header->xloadflags & XLF_5LEVEL) && pgtable_l5_enabled()) {
> > + pr_err("Can not jump to old 4-level kernel from 5-level kernel.\n");
>
> 4-level kernel sounds not very clear, maybe something like below?
>
> "5-level paging enabled, can not kexec into an old kernel without 5-level
> paging facility"?

Oops, tglx commented on this message. He suggested changing it like:

"bzImage cannot handle 5-level paging mode\n"

I forgot updating this part. Any one is fine to me. Will update.

Thanks
Baoquan

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