From: Heiko Carstens hca@linux.ibm.com
commit 2862a2fdfae875888e3c1c3634e3422e01d98147 upstream.
Use "a" constraint instead of "d" constraint to pass the state parameter to the do_sqbs() inline assembly. This prevents that general purpose register zero is used for the state parameter.
If the compiler would select general purpose register zero this would be problematic for the used instruction in rsy format: the register used for the state parameter is a base register. If the base register is general purpose register zero the contents of the register are unexpectedly ignored when the instruction is executed.
This only applies to z/VM guests using QIOASSIST with dedicated (pass through) QDIO-based devices such as FCP [zfcp driver] as well as real OSA or HiperSockets [qeth driver].
A possible symptom for this case using zfcp is the following repeating kernel message pattern:
zfcp <devbusid>: A QDIO problem occurred zfcp <devbusid>: A QDIO problem occurred zfcp <devbusid>: qdio: ZFCP on SC <sc> using AI:1 QEBSM:1 PRI:1 TDD:1 SIGA: W zfcp <devbusid>: A QDIO problem occurred zfcp <devbusid>: A QDIO problem occurred
Each of the qdio problem message can be accompanied by the following entries for the affected subchannel <sc> in /sys/kernel/debug/s390dbf/qdio_error/hex_ascii for zfcp or qeth:
<sc> ccq: 69.... <sc> SQBS ERROR.
Reviewed-by: Benjamin Block bblock@linux.ibm.com Cc: Steffen Maier maier@linux.ibm.com Fixes: 8129ee164267 ("[PATCH] s390: qdio V=V pass-through") Cc: stable@vger.kernel.org Signed-off-by: Heiko Carstens hca@linux.ibm.com Signed-off-by: Alexander Gordeev agordeev@linux.ibm.com Signed-off-by: Greg Kroah-Hartman gregkh@linuxfoundation.org --- drivers/s390/cio/qdio.h | 2 +- 1 file changed, 1 insertion(+), 1 deletion(-)
--- a/drivers/s390/cio/qdio.h +++ b/drivers/s390/cio/qdio.h @@ -95,7 +95,7 @@ static inline int do_sqbs(u64 token, uns " lgr 1,%[token]\n" " .insn rsy,0xeb000000008a,%[qs],%[ccq],0(%[state])" : [ccq] "+&d" (_ccq), [qs] "+&d" (_queuestart) - : [state] "d" ((unsigned long)state), [token] "d" (token) + : [state] "a" ((unsigned long)state), [token] "d" (token) : "memory", "cc", "1"); *count = _ccq & 0xff; *start = _queuestart & 0xff;