1d89cb2c72
commit 028a73e10705af1ffd51f2537460f616dc58680e upstream.
On some servers with MGA G200_SE_A (rev 42), booting with Legacy BIOS,
the hardware hangs when using kdump and kexec into the kdump kernel.
This happens when the uncompress code tries to write "Decompressing Linux"
to the VGA Console.
It can be reproduced by writing to the VGA console (0xB8000) after
booting to graphic mode, it generates the following error:
kernel:NMI: PCI system error (SERR) for reason a0 on CPU 0.
kernel:Dazed and confused, but trying to continue
The root cause is the configuration of the MGA GCTL6 register
According to the GCTL6 register documentation:
bit 0 is gcgrmode:
0: Enables alpha mode, and the character generator addressing system is
activated.
1: Enables graphics mode, and the character addressing system is not
used.
bit 1 is chainodd even:
0: The A0 signal of the memory address bus is used during system memory
addressing.
1: Allows A0 to be replaced by either the A16 signal of the system
address (ifmemmapsl is ‘00’), or by the hpgoddev (MISC<5>, odd/even
page select) field, described on page 3-294).
bit 3-2 are memmapsl:
Memory map select bits 1 and 0. VGA.
These bits select where the video memory is mapped, as shown below:
00 => A0000h - BFFFFh
01 => A0000h - AFFFFh
10 => B0000h - B7FFFh
11 => B8000h - BFFFFh
bit 7-4 are reserved.
Current code set it to 0x05 => memmapsl to b01 => 0xa0000 (graphic mode)
But on x86, the VGA console is at 0xb8000 (text mode)
In arch/x86/boot/compressed/misc.c debug strings are written to 0xb8000
As the driver doesn't use this mapping at 0xa0000, it is safe to set it to
0xb8000 instead, to avoid kernel hang on G200_SE_A rev42, with kexec/kdump.
Thus changing the value 0x05 to 0x0d
Signed-off-by: Jocelyn Falempe <jfalempe@redhat.com>
Reviewed-by: Javier Martinez Canillas <javierm@redhat.com>
Acked-by: Lyude Paul <lyude@redhat.com>
Cc: stable@vger.kernel.org
Signed-off-by: Thomas Zimmermann <tzimmermann@suse.de>
Link: https://patchwork.freedesktop.org/patch/msgid/20220119102905.1194787-1-jfalempe@redhat.com
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Linux kernel
============
There are several guides for kernel developers and users. These guides can
be rendered in a number of formats, like HTML and PDF. Please read
Documentation/admin-guide/README.rst first.
In order to build the documentation, use ``make htmldocs`` or
``make pdfdocs``. The formatted documentation can also be read online at:
https://www.kernel.org/doc/html/latest/
There are various text files in the Documentation/ subdirectory,
several of them using the Restructured Text markup notation.
Please read the Documentation/process/changes.rst file, as it contains the
requirements for building and running the kernel, and information about
the problems which may result by upgrading your kernel.