On Wed, 26 Jul 2017 11:40:14 +0200 Cornelia Huck <cohuck@xxxxxxxxxx> wrote: > On Wed, 26 Jul 2017 07:40:44 +0200 > Martin Schwidefsky <schwidefsky@xxxxxxxxxx> wrote: > > > On Wed, 26 Jul 2017 07:00:33 +0200 > > Heiko Carstens <heiko.carstens@xxxxxxxxxx> wrote: > > > > > On Tue, Jul 25, 2017 at 06:14:51PM -0700, Guenter Roeck wrote: > > > > Hi Martin, > > > > > > > > my s390 qemu tests in linux-next stopped working a few days ago. > > > > Bisect points to commit 's390/spinlock: add niai spinlock hints'. > > > > > > > > Looking at the patch, this isn't really surprising; at least to me it looks > > > > like the patch is making instructions mandatory which are only available in > > > > Z14 CPUs. Does this mean that older s390 CPUs (such as the Z900 used in my > > > > qemu tests) are no longer going to be supported in Linux ? > > > > > > No, that means that the patch has a bug. The NIAI instruction is only > > > available if the execution-hint facility is installed. That facility came > > > with zEC12. Luckily it uses the same facility indicator bit like the > > > miscellaneous-instruction-extensions facility, which we already use anyway > > > if the kernel gets compiled for zEC12. In that case we have early code > > > which verifies if all required facilities to run the kernel are installed, > > > and if not it will print a message to the console and stop the machine. > > > > > > So the easiest fix would be to generate the NIAI instruction only if the > > > kernel gets compiled for zEC12 or newer. > > > > Hmm, I though that NIAI is a NOP on older machines. > > FWIW, the upcoming qemu 2.11 (in tcg mode) will support to activate > stfle bit 49 and generate NOPs for NIAI and friends. > > If I read the PoP correctly, the only correct way is to check for stfle > bit 49 before trying to use NIAI. While a real zEC12 or later probably > will have the facility, you can withdraw the feature bit via the cpu > model when running under qemu. A kernel compiled for ZEC12 or later will check STFLE bit 49 at boot time and crash if the bit is not set. -- blue skies, Martin. "Reality continues to ruin my life." - Calvin. -- To unsubscribe from this list: send the line "unsubscribe linux-s390" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
