4.14-stable review patch. If anyone has any objections, please let me know.
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From: Heiko Carstens heiko.carstens@de.ibm.com
commit d0e810eeb3d326978f248b8f0233a2f30f58c72d upstream.
Rebooting into a new kernel with kexec fails (system dies) if tried on a machine that has no-execute support. Reason for this is that the so called datamover code gets executed with DAT on (MMU is active) and the page that contains the datamover is marked as non-executable. Therefore when branching into the datamover an unexpected program check happens and afterwards the machine is dead.
This can be simply avoided by disabling DAT, which also disables any no-execute checks, just before the datamover gets executed.
In fact the first thing done by the datamover is to disable DAT. The code in the datamover that disables DAT can be removed as well.
Thanks to Michael Holzheu and Gerald Schaefer for tracking this down.
Reviewed-by: Michael Holzheu holzheu@linux.vnet.ibm.com Reviewed-by: Philipp Rudo prudo@linux.vnet.ibm.com Cc: Gerald Schaefer gerald.schaefer@de.ibm.com Cc: Martin Schwidefsky schwidefsky@de.ibm.com Fixes: 57d7f939e7bd ("s390: add no-execute support") Signed-off-by: Heiko Carstens heiko.carstens@de.ibm.com Signed-off-by: Greg Kroah-Hartman gregkh@linuxfoundation.org
--- arch/s390/kernel/machine_kexec.c | 1 + arch/s390/kernel/relocate_kernel.S | 3 --- 2 files changed, 1 insertion(+), 3 deletions(-)
--- a/arch/s390/kernel/machine_kexec.c +++ b/arch/s390/kernel/machine_kexec.c @@ -269,6 +269,7 @@ static void __do_machine_kexec(void *dat s390_reset_system(); data_mover = (relocate_kernel_t) page_to_phys(image->control_code_page);
+ __arch_local_irq_stnsm(0xfb); /* disable DAT - avoid no-execute */ /* Call the moving routine */ (*data_mover)(&image->head, image->start);
--- a/arch/s390/kernel/relocate_kernel.S +++ b/arch/s390/kernel/relocate_kernel.S @@ -29,7 +29,6 @@ ENTRY(relocate_kernel) basr %r13,0 # base address .base: - stnsm sys_msk-.base(%r13),0xfb # disable DAT stctg %c0,%c15,ctlregs-.base(%r13) stmg %r0,%r15,gprregs-.base(%r13) lghi %r0,3 @@ -103,8 +102,6 @@ ENTRY(relocate_kernel) .align 8 load_psw: .long 0x00080000,0x80000000 - sys_msk: - .quad 0 ctlregs: .rept 16 .quad 0