the cpu state settable by user space.
This is necessary to avoid races in s390 SIGP/reset handling which
happen because some SIGPs are handled in QEMU, while others are
handled in the kernel. Together with the busy conditions as return
value of SIGP races happen especially in areas like starting and
stopping of CPUs. (For example, there is a program 'cpuplugd', that
runs on several s390 distros which does automatic onlining and
offlining on cpus.)
As soon as the MPSTATE interface is used, user space takes complete
control of the cpu states. Otherwise the kernel will use the old way.
Therefore, the new kernel continues to work fine with old QEMUs.
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Merge tag 'kvm-s390-20140715' of git://git.kernel.org/pub/scm/linux/kernel/git/kvms390/linux into kvm-next
This series enables the "KVM_(S|G)ET_MP_STATE" ioctls on s390 to make
the cpu state settable by user space.
This is necessary to avoid races in s390 SIGP/reset handling which
happen because some SIGPs are handled in QEMU, while others are
handled in the kernel. Together with the busy conditions as return
value of SIGP races happen especially in areas like starting and
stopping of CPUs. (For example, there is a program 'cpuplugd', that
runs on several s390 distros which does automatic onlining and
offlining on cpus.)
As soon as the MPSTATE interface is used, user space takes complete
control of the cpu states. Otherwise the kernel will use the old way.
Therefore, the new kernel continues to work fine with old QEMUs.
ec10b72701