-----Original Message-----
> Hi Kazu,
> On Tue, Mar 22, 2022 at 07:29:41AM +0000, HAGIO KAZUHITO(萩尾 一仁) wrote:
> > -----Original Message-----
> > > 1.) When I tested live system with "crash vmlinux /proc/kcore" in kernel
> > > v5.7,
> > > I met the following crash issue:
> > > ........................................
> > > crash: seek error: kernel virtual address: ffff75e9fffff000 type:
> > > "pud page"
> > > ........................................
> > >
> > > 2.) The root cause is the PTOV does not work correctly for some kernel,
> > > and then arm64_vtop_4level_4k() does not work correctly too.
> > >
> > > Why PTOV does not work?
> > >
> > > The PHYS_OFFSET is just wrapper of memstart_addr.
> > > ...............................
> > > #define PHYS_OFFSET ({ VM_BUG_ON(memstart_addr & 1); memstart_addr;
> > > })
> > > ...............................
> > >
> > > Because memstart_addr is changed after physvirt_offset is initialized.
> > > so the NUMBER(PHYS_OFFSET) does not return the correct value.
> >
> > Hmm, it looks like arm64_PTOV() uses the physvirt_offset if available
> > (5.4 <= kernel < 5.10), I'm still not sure why it does not work correctly.
> > Would you please explain the issue in more detail?
>
> In arm64_calc_physvirt_offset(void), we try to read out the
> physvirt_offset from the live system, and we call read_proc_kcore().
>
> In the read_proc_kcore:
> ................................................
> if (paddr == KCORE_USE_VADDR)
> kvaddr = addr;
> else
> kvaddr = PTOV((ulong)paddr);
> ................................................
>
> We need the PTOV (arm64_PTOV()) to work correctly.
>
> Unfortunately, arm64_PTOV() uses the ms->phys_offset again..
> ................................................
> ulong arm64_PTOV(ulong paddr)
> {
> struct machine_specific *ms = machdep->machspec;
>
> /*
> * Either older kernel before kernel has 'physvirt_offset' or
> newer
> * kernel which removes 'physvirt_offset' has the same formula:
> * #define __phys_to_virt(x) ((unsigned long)((x) -
> PHYS_OFFSET) | PAGE_OFFSET)
> */
> if (!(machdep->flags & HAS_PHYSVIRT_OFFSET))
> return (paddr - ms->phys_offset) | PAGE_OFFSET;
> else
> return paddr - ms->physvirt_offset;
> }
> ................................................
>
> So the physvirt_offset depends on the NUMBER(PHYS_OFFSET).
Thank you for the explanation.
So does using symbol_value_from_proc_kallsyms() and KCORE_USE_VADDR work?
Several functions in arm64.c already use this way:
if (kernel_symbol_exists("vabits_actual")) {
if (pc->flags & PROC_KCORE) {
vabits_actual =
symbol_value_from_proc_kallsyms("vabits_actual");
if ((vabits_actual != BADVAL) && (READMEM(pc->mfd,
&value, sizeof(ulong),
vabits_actual, KCORE_USE_VADDR) > 0)) {
Thanks,
Kazu
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