From: Alexander Gordeev agordeev@linux.ibm.com
[ Upstream commit 29ccaa4b35ea874ddd50518e5c2c746b9238a792 ]
Commit d768bd892fc8 ("s390: add options to change branch prediction behaviour for the kernel") introduced .Lsie_exit label - supposedly to fence off SIE instruction. However, the corresponding address range length .Lsie_crit_mcck_length was not updated, which led to BPON code potentionally marked with CIF_MCCK_GUEST flag.
Both .Lsie_exit and .Lsie_crit_mcck_length were removed with commit 0b0ed657fe00 ("s390: remove critical section cleanup from entry.S"), but the issue persisted - currently BPOFF and BPENTER macros might get wrongly considered by the machine check handler as a guest.
Fixes: d768bd892fc8 ("s390: add options to change branch prediction behaviour for the kernel") Reviewed-by: Sven Schnelle svens@linux.ibm.com Reviewed-by: Christian Borntraeger borntraeger@linux.ibm.com Signed-off-by: Alexander Gordeev agordeev@linux.ibm.com Signed-off-by: Heiko Carstens hca@linux.ibm.com Signed-off-by: Sasha Levin sashal@kernel.org --- arch/s390/kernel/entry.S | 6 +++++- 1 file changed, 5 insertions(+), 1 deletion(-)
diff --git a/arch/s390/kernel/entry.S b/arch/s390/kernel/entry.S index 4c9b967290ae..d530eb4dc413 100644 --- a/arch/s390/kernel/entry.S +++ b/arch/s390/kernel/entry.S @@ -248,6 +248,10 @@ ENTRY(sie64a) BPEXIT __SF_SIE_FLAGS(%r15),(_TIF_ISOLATE_BP|_TIF_ISOLATE_BP_GUEST) .Lsie_entry: sie 0(%r14) +# Let the next instruction be NOP to avoid triggering a machine check +# and handling it in a guest as result of the instruction execution. + nopr 7 +.Lsie_leave: BPOFF BPENTER __SF_SIE_FLAGS(%r15),(_TIF_ISOLATE_BP|_TIF_ISOLATE_BP_GUEST) .Lsie_skip: @@ -536,7 +540,7 @@ ENTRY(mcck_int_handler) jno .Lmcck_panic #if IS_ENABLED(CONFIG_KVM) OUTSIDE %r9,.Lsie_gmap,.Lsie_done,6f - OUTSIDE %r9,.Lsie_entry,.Lsie_skip,4f + OUTSIDE %r9,.Lsie_entry,.Lsie_leave,4f oi __LC_CPU_FLAGS+7, _CIF_MCCK_GUEST j 5f 4: CHKSTG .Lmcck_panic