Merge branch 'ppc-bundle' (bundle from Michael Ellerman)

Merge powerpc transactional memory fixes from Michael Ellerman:
 "I figured I'd still send you the commits using a bundle to make sure
  it works in case I need to do it again in future"

This fixes transactional memory state restore for powerpc.

* bundle'd patches from Michael Ellerman:
  powerpc/tm: Fix illegal TM state in signal handler
  powerpc/64s: Use emergency stack for kernel TM Bad Thing program checks

2 files changed, 35 insertions, 2 deletions

diff --git a/arch/powerpc/kernel/exceptions-64s.S b/arch/powerpc/kernel/exceptions-64s.S
index 48da0f5..b82586c 100644
--- a/arch/powerpc/kernel/exceptions-64s.S
+++ b/arch/powerpc/kernel/exceptions-64s.S
@@ -734,7 +734,29 @@ EXC_REAL(program_check, 0x700, 0x100)
 EXC_VIRT(program_check, 0x4700, 0x100, 0x700)
 TRAMP_KVM(PACA_EXGEN, 0x700)
 EXC_COMMON_BEGIN(program_check_common)
-	EXCEPTION_PROLOG_COMMON(0x700, PACA_EXGEN)
+	/*
+	 * It's possible to receive a TM Bad Thing type program check with
+	 * userspace register values (in particular r1), but with SRR1 reporting
+	 * that we came from the kernel. Normally that would confuse the bad
+	 * stack logic, and we would report a bad kernel stack pointer. Instead
+	 * we switch to the emergency stack if we're taking a TM Bad Thing from
+	 * the kernel.
+	 */
+	li	r10,MSR_PR		/* Build a mask of MSR_PR ..	*/
+	oris	r10,r10,0x200000@h	/* .. and SRR1_PROGTM		*/
+	and	r10,r10,r12		/* Mask SRR1 with that.		*/
+	srdi	r10,r10,8		/* Shift it so we can compare	*/
+	cmpldi	r10,(0x200000 >> 8)	/* .. with an immediate.	*/
+	bne 1f				/* If != go to normal path.	*/
+
+	/* SRR1 had PR=0 and SRR1_PROGTM=1, so use the emergency stack	*/
+	andi.	r10,r12,MSR_PR;		/* Set CR0 correctly for label	*/
+					/* 3 in EXCEPTION_PROLOG_COMMON	*/
+	mr	r10,r1			/* Save r1			*/
+	ld	r1,PACAEMERGSP(r13)	/* Use emergency stack		*/
+	subi	r1,r1,INT_FRAME_SIZE	/* alloc stack frame		*/
+	b 3f				/* Jump into the macro !!	*/
+1:	EXCEPTION_PROLOG_COMMON(0x700, PACA_EXGEN)
 	bl	save_nvgprs
 	RECONCILE_IRQ_STATE(r10, r11)
 	addi	r3,r1,STACK_FRAME_OVERHEAD
diff --git a/arch/powerpc/kernel/signal_64.c b/arch/powerpc/kernel/signal_64.c
index c83c115..b2c0029 100644
--- a/arch/powerpc/kernel/signal_64.c
+++ b/arch/powerpc/kernel/signal_64.c
@@ -452,9 +452,20 @@ static long restore_tm_sigcontexts(struct task_struct *tsk,
 	if (MSR_TM_RESV(msr))
 		return -EINVAL;
 
-	/* pull in MSR TM from user context */
+	/* pull in MSR TS bits from user context */
 	regs->msr = (regs->msr & ~MSR_TS_MASK) | (msr & MSR_TS_MASK);
 
+	/*
+	 * Ensure that TM is enabled in regs->msr before we leave the signal
+	 * handler. It could be the case that (a) user disabled the TM bit
+	 * through the manipulation of the MSR bits in uc_mcontext or (b) the
+	 * TM bit was disabled because a sufficient number of context switches
+	 * happened whilst in the signal handler and load_tm overflowed,
+	 * disabling the TM bit. In either case we can end up with an illegal
+	 * TM state leading to a TM Bad Thing when we return to userspace.
+	 */
+	regs->msr |= MSR_TM;
+
 	/* pull in MSR LE from user context */
 	regs->msr = (regs->msr & ~MSR_LE) | (msr & MSR_LE);