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s390/startup: add initial pgm check handler 

The startup code is getting more complicated with features like kaslr and
secure boot in place. In a potential unexpected startup code crash case
the system would end up in a pgm check loop at address 0, overwriting
pgm check old psw value and just making debugging more complicated. To
avoid that introduce startup program check handler which is active
immediately after kernel start and until early_pgm_check_handler is set
in kernel/early.c. So it covers kernel relocation phase and transition
to it. This pgm check handler simply saves general/control registers and
psw in the save area which should guarantee that we still have something
to look at when standalone dumper is called without saving registers. And
it does disabled wait with a faulty address in the end.

Acked-by: Ilya Leoshkevich <iii@linux.ibm.com>
Signed-off-by: Vasily Gorbik <gor@linux.ibm.com>
This commit is contained in:
Vasily Gorbik 2019-08-08 13:50:02 +02:00
parent 40e90656c1
commit da9ed30d29
1 changed files with 23 additions and 1 deletions
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24
arch/s390/boot/head.S
View File

@ -60,8 +60,10 @@ __HEAD
.long 0x02000690,0x60000050
.long 0x020006e0,0x20000050
.org 0x1a0
.org __LC_RST_NEW_PSW # 0x1a0
.quad 0,iplstart
.org __LC_PGM_NEW_PSW # 0x1d0
.quad 0x0000000180000000,startup_pgm_check_handler
.org 0x200
@ -351,6 +353,26 @@ ENTRY(startup_kdump)
#include "head_kdump.S"
#
# This program check is active immediately after kernel start
# and until early_pgm_check_handler is set in kernel/early.c
# It simply saves general/control registers and psw in
# the save area and does disabled wait with a faulty address.
#
ENTRY(startup_pgm_check_handler)
stmg %r0,%r15,__LC_SAVE_AREA_SYNC
la %r1,4095
stctg %c0,%c15,__LC_CREGS_SAVE_AREA-4095(%r1)
mvc __LC_GPREGS_SAVE_AREA-4095(128,%r1),__LC_SAVE_AREA_SYNC
mvc __LC_PSW_SAVE_AREA-4095(16,%r1),__LC_PGM_OLD_PSW
lg %r1,__LC_SAVE_AREA_SYNC+8
mvc __LC_RETURN_PSW(16),__LC_PGM_OLD_PSW
ni __LC_RETURN_PSW,0xfc # remove IO and EX bits
ni __LC_RETURN_PSW+1,0xfb # remove MCHK bit
oi __LC_RETURN_PSW+1,0x2 # set wait state bit
lpswe __LC_RETURN_PSW # disabled wait
ENDPROC(startup_pgm_check_handler)
#
# params at 10400 (setup.h)
# Must be keept in sync with struct parmarea in setup.h