[PATCH 4.14 142/183] powerpc: Fix 32-bit KVM-PR lockup and host crash with MacOS guest

From: Greg Kroah-Hartman
Date: Fri Mar 22 2019 - 08:51:32 EST

4.14-stable review patch. If anyone has any objections, please let me know.


From: Mark Cave-Ayland <mark.cave-ayland@xxxxxxxxxxxx>

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@xxxxxxxxxxxxxxx # v4.6+
Signed-off-by: Mark Cave-Ayland <mark.cave-ayland@xxxxxxxxxxxx>
Signed-off-by: Michael Ellerman <mpe@xxxxxxxxxxxxxx>
Signed-off-by: Greg Kroah-Hartman <gregkh@xxxxxxxxxxxxxxxxxxx>

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
@@ -156,7 +156,7 @@ void __giveup_fpu(struct task_struct *ts

msr = tsk->thread.regs->msr;
- msr &= ~MSR_FP;
+ msr &= ~(MSR_FP|MSR_FE0|MSR_FE1);
if (cpu_has_feature(CPU_FTR_VSX))
msr &= ~MSR_VSX;