[PATCH v8 28/30] powerpc: Support prefixed instructions in alignment handler

[Jordan Niethe]

If a prefixed instruction results in an alignment exception, the
SRR1_PREFIXED bit is set. The handler attempts to emulate the
responsible instruction and then increment the NIP past it. Use
SRR1_PREFIXED to determine by how much the NIP should be incremented.

Prefixed instructions are not permitted to cross 64-byte boundaries. If
they do the alignment interrupt is invoked with SRR1 BOUNDARY bit set.
If this occurs send a SIGBUS to the offending process if in user mode.
If in kernel mode call bad_page_fault().

Reviewed-by: Alistair Popple <alistair at popple.id.au>
Signed-off-by: Jordan Niethe <jniethe5 at gmail.com>
---
v2: - Move __get_user_instr() and __get_user_instr_inatomic() to this
commit (previously in "powerpc sstep: Prepare to support prefixed
instructions").
    - Rename sufx to suffix
    - Use a macro for calculating instruction length
v3: Move __get_user_{instr(), instr_inatomic()} up with the other
get_user definitions and remove nested if.
v4: Rolled into "Add prefixed instructions to instruction data type"
v5: Only one definition of inst_length()
---
 arch/powerpc/kernel/traps.c | 19 ++++++++++++++++++-
 1 file changed, 18 insertions(+), 1 deletion(-)

diff --git a/arch/powerpc/kernel/traps.c b/arch/powerpc/kernel/traps.c
index 493a3fa0ac1a..105242cc2f28 100644
--- a/arch/powerpc/kernel/traps.c
+++ b/arch/powerpc/kernel/traps.c
@@ -583,6 +583,8 @@ static inline int check_io_access(struct pt_regs *regs)
 #define REASON_ILLEGAL		(ESR_PIL | ESR_PUO)
 #define REASON_PRIVILEGED	ESR_PPR
 #define REASON_TRAP		ESR_PTR
+#define REASON_PREFIXED		0
+#define REASON_BOUNDARY		0
 
 /* single-step stuff */
 #define single_stepping(regs)	(current->thread.debug.dbcr0 & DBCR0_IC)
@@ -597,12 +599,16 @@ static inline int check_io_access(struct pt_regs *regs)
 #define REASON_ILLEGAL		SRR1_PROGILL
 #define REASON_PRIVILEGED	SRR1_PROGPRIV
 #define REASON_TRAP		SRR1_PROGTRAP
+#define REASON_PREFIXED		SRR1_PREFIXED
+#define REASON_BOUNDARY		SRR1_BOUNDARY
 
 #define single_stepping(regs)	((regs)->msr & MSR_SE)
 #define clear_single_step(regs)	((regs)->msr &= ~MSR_SE)
 #define clear_br_trace(regs)	((regs)->msr &= ~MSR_BE)
 #endif
 
+#define inst_length(reason)	(((reason) & REASON_PREFIXED) ? 8 : 4)
+
 #if defined(CONFIG_E500)
 int machine_check_e500mc(struct pt_regs *regs)
 {
@@ -1593,11 +1599,20 @@ void alignment_exception(struct pt_regs *regs)
 {
 	enum ctx_state prev_state = exception_enter();
 	int sig, code, fixed = 0;
+	unsigned long  reason;
 
 	/* We restore the interrupt state now */
 	if (!arch_irq_disabled_regs(regs))
 		local_irq_enable();
 
+	reason = get_reason(regs);
+
+	if (reason & REASON_BOUNDARY) {
+		sig = SIGBUS;
+		code = BUS_ADRALN;
+		goto bad;
+	}
+
 	if (tm_abort_check(regs, TM_CAUSE_ALIGNMENT | TM_CAUSE_PERSISTENT))
 		goto bail;
 
@@ -1606,7 +1621,8 @@ void alignment_exception(struct pt_regs *regs)
 		fixed = fix_alignment(regs);
 
 	if (fixed == 1) {
-		regs->nip += 4;	/* skip over emulated instruction */
+		/* skip over emulated instruction */
+		regs->nip += inst_length(reason);
 		emulate_single_step(regs);
 		goto bail;
 	}
@@ -1619,6 +1635,7 @@ void alignment_exception(struct pt_regs *regs)
 		sig = SIGBUS;
 		code = BUS_ADRALN;
 	}
+bad:
 	if (user_mode(regs))
 		_exception(sig, regs, code, regs->dar);
 	else
-- 
2.17.1