Re: [Crash-utility] [PATCH 2/2] arm64: fix the "pud page" crash for live system
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).
Thanks
Huang Shijie