• Mark Cave-Ayland's avatar
    powerpc: Fix 32-bit KVM-PR lockup and host crash with MacOS guest · 344996a8
    Mark Cave-Ayland authored
    commit fe1ef6bc upstream.
    
    Commit 8792468d "powerpc: Add the ability to save FPU without
    giving it up" unexpectedly removed the MSR_FE0 and MSR_FE1 bits from
    the bitmask used to update the MSR of the previous thread in
    __giveup_fpu() causing a KVM-PR MacOS guest to lockup and panic the
    host kernel.
    
    Leaving FE0/1 enabled means unrelated processes might receive FPEs
    when they're not expecting them and crash. In particular if this
    happens to init the host will then panic.
    
    eg (transcribed):
      qemu-system-ppc[837]: unhandled signal 8 at 12cc9ce4 nip 12cc9ce4 lr 12cc9ca4 code 0
      systemd[1]: unhandled signal 8 at 202f02e0 nip 202f02e0 lr 001003d4 code 0
      Kernel panic - not syncing: Attempted to kill init! exitcode=0x0000000b
    
    Reinstate these bits to the MSR bitmask to enable MacOS guests to run
    under 32-bit KVM-PR once again without issue.
    
    Fixes: 8792468d ("powerpc: Add the ability to save FPU without giving it up")
    Cc: stable@vger.kernel.org # v4.6+
    Signed-off-by: default avatarMark Cave-Ayland <mark.cave-ayland@ilande.co.uk>
    Signed-off-by: default avatarMichael Ellerman <mpe@ellerman.id.au>
    Signed-off-by: default avatarGreg Kroah-Hartman <gregkh@linuxfoundation.org>
    344996a8
process.c 55.8 KB