4.9-stable review patch. If anyone has any objections, please let me know.
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From: Mark Cave-Ayland mark.cave-ayland@ilande.co.uk
commit fe1ef6bcdb4fca33434256a802a3ed6aacf0bd2f upstream.
Commit 8792468da5e1 "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: 8792468da5e1 ("powerpc: Add the ability to save FPU without giving it up") Cc: stable@vger.kernel.org # v4.6+ Signed-off-by: Mark Cave-Ayland mark.cave-ayland@ilande.co.uk Signed-off-by: Michael Ellerman mpe@ellerman.id.au Signed-off-by: Greg Kroah-Hartman gregkh@linuxfoundation.org
--- arch/powerpc/kernel/process.c | 2 +- 1 file changed, 1 insertion(+), 1 deletion(-)
--- a/arch/powerpc/kernel/process.c +++ b/arch/powerpc/kernel/process.c @@ -153,7 +153,7 @@ void __giveup_fpu(struct task_struct *ts
save_fpu(tsk); msr = tsk->thread.regs->msr; - msr &= ~MSR_FP; + msr &= ~(MSR_FP|MSR_FE0|MSR_FE1); #ifdef CONFIG_VSX if (cpu_has_feature(CPU_FTR_VSX)) msr &= ~MSR_VSX;