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    • S
      powerpc/powernv: Restore non-volatile CRs after nap · 0aab3747
      Sam Bobroff 提交于
      Patches 7cba160a "powernv/cpuidle: Redesign idle states management"
      and 77b54e9f "powernv/powerpc: Add winkle support for offline cpus"
      use non-volatile condition registers (cr2, cr3 and cr4) early in the system
      reset interrupt handler (system_reset_pSeries()) before it has been determined
      if state loss has occurred. If state loss has not occurred, control returns via
      the power7_wakeup_noloss() path which does not restore those condition
      registers, leaving them corrupted.
      
      Fix this by restoring the condition registers in the power7_wakeup_noloss()
      case.
      
      This is apparent when running a KVM guest on hardware that does not
      support winkle or sleep and the guest makes use of secondary threads. In
      practice this means Power7 machines, though some early unreleased Power8
      machines may also be susceptible.
      
      The secondary CPUs are taken off line before the guest is started and
      they call pnv_smp_cpu_kill_self(). This checks support for sleep
      states (in this case there is no support) and power7_nap() is called.
      
      When the CPU is woken, power7_nap() returns and because the CPU is
      still off line, the main while loop executes again. The sleep states
      support test is executed again, but because the tested values cannot
      have changed, the compiler has optimized the test away and instead we
      rely on the result of the first test, which has been left in cr3
      and/or cr4. With the result overwritten, the wrong branch is taken and
      power7_winkle() is called on a CPU that does not support it, leading
      to it stalling.
      
      Fixes: 7cba160a ("powernv/cpuidle: Redesign idle states management")
      Fixes: 77b54e9f ("powernv/powerpc: Add winkle support for offline cpus")
      [mpe: Massage change log a bit more]
      Signed-off-by: NSam Bobroff <sam.bobroff@au1.ibm.com>
      Signed-off-by: NMichael Ellerman <mpe@ellerman.id.au>
      0aab3747