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

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Date:   Fri, 22 Mar 2019 12:16:10 +0100
From:   Greg Kroah-Hartman <gregkh@...uxfoundation.org>
To:     linux-kernel@...r.kernel.org
Cc:     Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        stable@...r.kernel.org,
        Mark Cave-Ayland <mark.cave-ayland@...nde.co.uk>,
        Michael Ellerman <mpe@...erman.id.au>
Subject: [PATCH 4.14 142/183] powerpc: Fix 32-bit KVM-PR lockup and host crash with MacOS guest

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

------------------

From: Mark Cave-Ayland <mark.cave-ayland@...nde.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@...r.kernel.org # v4.6+
Signed-off-by: Mark Cave-Ayland <mark.cave-ayland@...nde.co.uk>
Signed-off-by: Michael Ellerman <mpe@...erman.id.au>
Signed-off-by: Greg Kroah-Hartman <gregkh@...uxfoundation.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
@@ -156,7 +156,7 @@ 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;