----- Original Message -----
> Hi Kazu,
>
> On 02/20/2019 02:17 AM, Kazuhito Hagio wrote:
> > Hi Bhupesh,
> >
> > -----Original Message-----
> >> I am not sure you got a chance to look at the two regression cases I
> >> reported here:
> >> <http://lists.infradead.org/pipermail/kexec/2019-February/022449.html>
> >>
> >> Unfortunately the above suggestion doesn't provide any fix for
> >> ARMv8.2-LPA regression (see text under heading '
> >> (1). Regression Case 1 (ARMv8.2-LPA enabled kernel)')
> >
> > As for MAX_PHYSMEM_BITS, I realized that ppc64 makedumpfile can detect
> > it because there is only one SECTION_SIZE_BITS for ppc64. I think we
> > can use the same way as set_ppc64_max_physmem_bits() does also for
> > arm64 for now. I'm going to write it for kernels not having
> > NUMBER(MAX_PHYSMEM_BITS) in vmcoreinfo.
>
> I see two drawbacks with the above approach:
>
> a). This means that other user-space tools like crash-utility would
> still be broken and would probably need to find MAX_PHYSMEM_BITS for
> arm64 via a similar (hack'ish ?) approach.
>
> b). I am looking at the makedumpfile code for 'MAX_PHYSMEM_BITS'
> determination for two archs as an example:
>
> ppc
> ---
>
> int
> set_ppc64_max_physmem_bits(void)
> {
> long array_len = ARRAY_LENGTH(mem_section);
> /*
> * The older ppc64 kernels uses _MAX_PHYSMEM_BITS as 42 and the
> * newer kernels 3.7 onwards uses 46 bits.
> */
>
> info->max_physmem_bits = _MAX_PHYSMEM_BITS_ORIG ;
> if ((array_len == (NR_MEM_SECTIONS() / _SECTIONS_PER_ROOT_EXTREME()))
> || (array_len == (NR_MEM_SECTIONS() / _SECTIONS_PER_ROOT())))
> return TRUE;
>
> info->max_physmem_bits = _MAX_PHYSMEM_BITS_3_7;
> if ((array_len == (NR_MEM_SECTIONS() / _SECTIONS_PER_ROOT_EXTREME()))
> || (array_len == (NR_MEM_SECTIONS() / _SECTIONS_PER_ROOT())))
> return TRUE;
>
> info->max_physmem_bits = _MAX_PHYSMEM_BITS_4_19;
> if ((array_len == (NR_MEM_SECTIONS() / _SECTIONS_PER_ROOT_EXTREME()))
> || (array_len == (NR_MEM_SECTIONS() / _SECTIONS_PER_ROOT())))
> return TRUE;
>
> info->max_physmem_bits = _MAX_PHYSMEM_BITS_4_20;
> if ((array_len == (NR_MEM_SECTIONS() / _SECTIONS_PER_ROOT_EXTREME()))
> || (array_len == (NR_MEM_SECTIONS() /
> _SECTIONS_PER_ROOT())))
> return TRUE;
>
> return FALSE;
> }
>
> x86_64:
> ------
>
> int
> get_versiondep_info_x86_64(void)
> {
> /*
> * On linux-2.6.26, MAX_PHYSMEM_BITS is changed to 44 from 40.
> */
> if (info->kernel_version < KERNEL_VERSION(2, 6, 26))
> info->max_physmem_bits = _MAX_PHYSMEM_BITS_ORIG;
> else if (info->kernel_version < KERNEL_VERSION(2, 6, 31))
> info->max_physmem_bits = _MAX_PHYSMEM_BITS_2_6_26;
> else if(check_5level_paging())
> info->max_physmem_bits = _MAX_PHYSMEM_BITS_5LEVEL;
> else
> info->max_physmem_bits = _MAX_PHYSMEM_BITS_2_6_31;
>
> ...
> }
>
> Looking at the above, two questions come to my mind:
>
> - Do we really need all the above complexity in user-space code, to hoop
> across various kernel versions and perform allocations for something
> that can be so easily exported via vmcoreinfo? Also we need to see how
> portable is the above code for a new kernel version - IMO, it will need
> another fix patch when we update to a new kernel version in near future.
I agree -- not to mention that the "kernel version" way of determining things
does not account for distribution-specific backports.
>
> - Also do we need to replicate the above implementations across
> user-space tools when they can also utilize the vmcoreinfo information
> to determine the PA_BITS range without any additional arch/kernel
> version specific details as the single point of obtaining this
> information from the kernel?
>
> So, in view of the above, I would still advocate that we use a
> vmcoreinfo export for 'MAX_PHYSMEM_BITS' as well to have a uniform
> interface for the same across all user-land applications.
Again, totally agree.
Dave
> Thanks,
> Bhupesh
>
>
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