concurrency bug. Since all SLB/SR entries were invalidated during an
exception, a decrementer exception could cause the user segment to be
invalidated during a copyin()/copyout() without a thread switch that
would cause it to be restored from the PCB, potentially causing the
operation to continue on invalid memory. This is now handled by explicit
restoration of segment 12 from the PCB on 32-bit systems and a check in
the Data Segment Exception handler on 64-bit.
While here, cause copyin()/copyout() to check whether the requested
user segment is already installed, saving some pipeline flushes, and
fix the synchronization primitives around the mtsr and slbmte
instructions to prevent accessing stale segments.
MFC after: 2 weeks
Kernel sources for 64-bit PowerPC, along with build-system changes to keep
32-bit kernels compiling (build system changes for 64-bit kernels are
coming later). Existing 32-bit PowerPC kernel configurations must be
updated after this change to specify their architecture.
