Re: [PATCH v4 03/25] powerpc/fadump: Improve fadump documentation

[Mahesh Jagannath Salgaonkar <mahesh@linux.vnet.ibm.com>]

On 7/16/19 5:02 PM, Hari Bathini wrote:
> The figures depicting FADump's (Firmware-Assisted Dump) memory layout
> are missing some finer details like different memory regions and what
> they represent. Improve the documentation by updating those details.
> 
> Signed-off-by: Hari Bathini <hbathini@linux.ibm.com>
> ---
>  Documentation/powerpc/firmware-assisted-dump.txt |   65 ++++++++++++----------
>  1 file changed, 35 insertions(+), 30 deletions(-)
> 
> diff --git a/Documentation/powerpc/firmware-assisted-dump.txt b/Documentation/powerpc/firmware-assisted-dump.txt
> index 0c41d6d..e9b4e3c 100644
> --- a/Documentation/powerpc/firmware-assisted-dump.txt
> +++ b/Documentation/powerpc/firmware-assisted-dump.txt

This will have to be rebased now on firmware-assisted-dump.rst. However
Changes looks good to me.

Thanks,
-Mahesh.

> @@ -74,8 +74,9 @@ as follows:
>     there is crash data available from a previous boot. During
>     the early boot OS will reserve rest of the memory above
>     boot memory size effectively booting with restricted memory
> -   size. This will make sure that the second kernel will not
> -   touch any of the dump memory area.
> +   size. This will make sure that this kernel (also, referred
> +   to as second kernel or capture kernel) will not touch any
> +   of the dump memory area.
>  
>  -- User-space tools will read /proc/vmcore to obtain the contents
>     of memory, which holds the previous crashed kernel dump in ELF
> @@ -125,48 +126,52 @@ space memory except the user pages that were present in CMA region.
>  
>    o Memory Reservation during first kernel
>  
> -  Low memory                                         Top of memory
> -  0      boot memory size                                       |
> -  |           |                |<--Reserved dump area -->|      |
> -  V           V                |   Permanent Reservation |      V
> -  +-----------+----------/ /---+---+----+-----------+----+------+
> -  |           |                |CPU|HPTE|  DUMP     |ELF |      |
> -  +-----------+----------/ /---+---+----+-----------+----+------+
> -        |                                           ^
> -        |                                           |
> -        \                                           /
> -         -------------------------------------------
> -          Boot memory content gets transferred to
> -          reserved area by firmware at the time of
> -          crash
> +  Low memory                                                Top of memory
> +  0      boot memory size      |<--Reserved dump area --->|      |
> +  |           |                |   Permanent Reservation  |      |
> +  V           V                |   (Preserve area)        |      V
> +  +-----------+----------/ /---+---+----+--------+---+----+------+
> +  |           |                |CPU|HPTE|  DUMP  |HDR|ELF |      |
> +  +-----------+----------/ /---+---+----+--------+---+----+------+
> +        |                                   ^      ^
> +        |                                   |      |
> +        \                                   /      |
> +         -----------------------------------     FADump Header
> +          Boot memory content gets transferred   (meta area)
> +          to reserved area by firmware at the
> +          time of crash
> +
>                     Fig. 1
>  
> +
>    o Memory Reservation during second kernel after crash
>  
> -  Low memory                                        Top of memory
> -  0      boot memory size                                       |
> -  |           |<------------- Reserved dump area ----------- -->|
> -  V           V                                                 V
> -  +-----------+----------/ /---+---+----+-----------+----+------+
> -  |           |                |CPU|HPTE|  DUMP     |ELF |      |
> -  +-----------+----------/ /---+---+----+-----------+----+------+
> +  Low memory                                                Top of memory
> +  0      boot memory size                                        |
> +  |           |<------------- Reserved dump area --------------->|
> +  V           V                |<---- Preserve area ----->|      V
> +  +-----------+----------/ /---+---+----+--------+---+----+------+
> +  |           |                |CPU|HPTE|  DUMP  |HDR|ELF |      |
> +  +-----------+----------/ /---+---+----+--------+---+----+------+
>          |                                              |
>          V                                              V
>     Used by second                                /proc/vmcore
>     kernel to boot
>                     Fig. 2
>  
> -Currently the dump will be copied from /proc/vmcore to a
> -a new file upon user intervention. The dump data available through
> -/proc/vmcore will be in ELF format. Hence the existing kdump
> -infrastructure (kdump scripts) to save the dump works fine with
> -minor modifications.
> +Currently the dump will be copied from /proc/vmcore to a new file upon
> +user intervention. The dump data available through /proc/vmcore will be
> +in ELF format. Hence the existing kdump infrastructure (kdump scripts)
> +to save the dump works fine with minor modifications. KDump scripts on
> +major Distro releases have already been modified to work seemlessly (no
> +user intervention in saving the dump) when FADump is used, instead of
> +KDump, as dump mechanism.
>  
>  The tools to examine the dump will be same as the ones
>  used for kdump.
>  
>  How to enable firmware-assisted dump (fadump):
> --------------------------------------
> +---------------------------------------------
>  
>  1. Set config option CONFIG_FA_DUMP=y and build kernel.
>  2. Boot into linux kernel with 'fadump=on' kernel cmdline option.
> @@ -189,7 +194,7 @@ NOTE: 1. 'fadump_reserve_mem=' parameter has been deprecated. Instead
>           old behaviour.
>  
>  Sysfs/debugfs files:
> -------------
> +-------------------
>  
>  Firmware-assisted dump feature uses sysfs file system to hold
>  the control files and debugfs file to display memory reserved region.
>