lib: sbi: abstract out insn decoding to unify mem fault handlers

This patch abstracts out the instruction decoding part of misaligned ld/st
fault handlers, so it can be reused by ld/st access fault handlers.
Also Added lb/lbu/sb decoding. (previously unreachable by misaligned fault)

sbi_trap_emulate_load/store is now the common handler which takes a `emu`
parameter that is responsible for emulating the misaligned or access fault.
The `emu` callback is expected to fixup the fault, and based on the return
code of `emu`, sbi_trap_emulate_load/store will:

  r/wlen => the fixup is successful and regs/mepc needs to be updated.
  0      => the fixup is successful, but regs/mepc should be left untouched
            (this is usually used if `emu` does `sbi_trap_redirect`)
  -err   => failed, sbi_trap_error will be called

For now, load/store access faults are blindly redirected. It will be
enhanced in the following patches.

Signed-off-by: Bo Gan <ganboing@gmail.com>
Reviewed-by: Anup Patel <anup@brainfault.org>

include/sbi/sbi_trap_ldst.h

@@ -13,7 +13,12 @@
 #include <sbi/sbi_types.h>
 #include <sbi/sbi_trap.h>
 
-struct sbi_trap_regs;
+union sbi_ldst_data {
+	u64 data_u64;
+	u32 data_u32;
+	u8 data_bytes[8];
+	ulong data_ulong;
+};
 
 int sbi_misaligned_load_handler(struct sbi_trap_regs *regs,
 				const struct sbi_trap_info *orig_trap);
@@ -21,4 +26,10 @@ int sbi_misaligned_load_handler(struct sbi_trap_regs *regs,
 int sbi_misaligned_store_handler(struct sbi_trap_regs *regs,
 				 const struct sbi_trap_info *orig_trap);
 
+int sbi_load_access_handler(struct sbi_trap_regs *regs,
+			    const struct sbi_trap_info *orig_trap);
+
+int sbi_store_access_handler(struct sbi_trap_regs *regs,
+			     const struct sbi_trap_info *orig_trap);
+
 #endif

lib/sbi/sbi_trap.c

@@ -299,10 +299,12 @@ struct sbi_trap_regs *sbi_trap_handler(struct sbi_trap_regs *regs)
 		msg = "illegal instruction handler failed";
 		break;
 	case CAUSE_MISALIGNED_LOAD:
+		sbi_pmu_ctr_incr_fw(SBI_PMU_FW_MISALIGNED_LOAD);
 		rc  = sbi_misaligned_load_handler(regs, &trap);
 		msg = "misaligned load handler failed";
 		break;
 	case CAUSE_MISALIGNED_STORE:
+		sbi_pmu_ctr_incr_fw(SBI_PMU_FW_MISALIGNED_STORE);
 		rc  = sbi_misaligned_store_handler(regs, &trap);
 		msg = "misaligned store handler failed";
 		break;
@@ -312,10 +314,15 @@ struct sbi_trap_regs *sbi_trap_handler(struct sbi_trap_regs *regs)
 		msg = "ecall handler failed";
 		break;
 	case CAUSE_LOAD_ACCESS:
+		sbi_pmu_ctr_incr_fw(SBI_PMU_FW_ACCESS_LOAD);
+		rc  = sbi_load_access_handler(regs, &trap);
+		msg = "load fault handler failed";
+		break;
 	case CAUSE_STORE_ACCESS:
-		sbi_pmu_ctr_incr_fw(mcause == CAUSE_LOAD_ACCESS ?
-			SBI_PMU_FW_ACCESS_LOAD : SBI_PMU_FW_ACCESS_STORE);
-		/* fallthrough */
+		sbi_pmu_ctr_incr_fw(SBI_PMU_FW_ACCESS_STORE);
+		rc  = sbi_store_access_handler(regs, &trap);
+		msg = "store fault handler failed";
+		break;
 	default:
 		/* If the trap came from S or U mode, redirect it there */
 		msg = "trap redirect failed";

lib/sbi/sbi_trap_ldst.c

@@ -16,11 +16,23 @@
 #include <sbi/sbi_trap.h>
 #include <sbi/sbi_unpriv.h>
 
-union reg_data {
-	u8 data_bytes[8];
-	ulong data_ulong;
-	u64 data_u64;
-};
+/**
+ * Load emulator callback:
+ *
+ * @return rlen=success, 0=success w/o regs modification, or negative error
+ */
+typedef int (*sbi_trap_ld_emulator)(int rlen, union sbi_ldst_data *out_val,
+				    struct sbi_trap_regs *regs,
+				    const struct sbi_trap_info *orig_trap);
+
+/**
+ * Store emulator callback:
+ *
+ * @return wlen=success, 0=success w/o regs modification, or negative error
+ */
+typedef int (*sbi_trap_st_emulator)(int wlen, union sbi_ldst_data in_val,
+				    struct sbi_trap_regs *regs,
+				    const struct sbi_trap_info *orig_trap);
 
 static ulong sbi_misaligned_tinst_fixup(ulong orig_tinst, ulong new_tinst,
 					ulong addr_offset)
@@ -34,15 +46,14 @@ static ulong sbi_misaligned_tinst_fixup(ulong orig_tinst, ulong new_tinst,
 		return orig_tinst | (addr_offset << SH_RS1);
 }
 
-int sbi_misaligned_load_handler(struct sbi_trap_regs *regs,
-				const struct sbi_trap_info *orig_trap)
+static int sbi_trap_emulate_load(struct sbi_trap_regs *regs,
+				 const struct sbi_trap_info *orig_trap,
+				 sbi_trap_ld_emulator emu)
 {
 	ulong insn, insn_len;
-	union reg_data val;
+	union sbi_ldst_data val = { 0 };
 	struct sbi_trap_info uptrap;
-	int i, fp = 0, shift = 0, len = 0;
-
-	sbi_pmu_ctr_incr_fw(SBI_PMU_FW_MISALIGNED_LOAD);
+	int rc, fp = 0, shift = 0, len = 0;
 
 	if (orig_trap->tinst & 0x1) {
 		/*
@@ -64,7 +75,12 @@ int sbi_misaligned_load_handler(struct sbi_trap_regs *regs,
 		insn_len = INSN_LEN(insn);
 	}
 
-	if ((insn & INSN_MASK_LW) == INSN_MATCH_LW) {
+	if ((insn & INSN_MASK_LB) == INSN_MATCH_LB) {
+		len   = 1;
+		shift = 8 * (sizeof(ulong) - len);
+	} else if ((insn & INSN_MASK_LBU) == INSN_MATCH_LBU) {
+		len = 1;
+	} else if ((insn & INSN_MASK_LW) == INSN_MATCH_LW) {
 		len   = 4;
 		shift = 8 * (sizeof(ulong) - len);
 #if __riscv_xlen == 64
@@ -134,17 +150,10 @@ int sbi_misaligned_load_handler(struct sbi_trap_regs *regs,
 		return sbi_trap_redirect(regs, orig_trap);
 	}
 
-	val.data_u64 = 0;
-	for (i = 0; i < len; i++) {
-		val.data_bytes[i] =
-			sbi_load_u8((void *)(orig_trap->tval + i), &uptrap);
-		if (uptrap.cause) {
-			uptrap.epc   = regs->mepc;
-			uptrap.tinst = sbi_misaligned_tinst_fixup(
-				orig_trap->tinst, uptrap.tinst, i);
-			return sbi_trap_redirect(regs, &uptrap);
-		}
-	}
+	rc = emu(len, &val, regs, orig_trap);
+
+	if (rc <= 0)
+		return rc;
 
 	if (!fp)
 		SET_RD(insn, regs, ((long)(val.data_ulong << shift)) >> shift);
@@ -160,15 +169,14 @@ int sbi_misaligned_load_handler(struct sbi_trap_regs *regs,
 	return 0;
 }
 
-int sbi_misaligned_store_handler(struct sbi_trap_regs *regs,
-				 const struct sbi_trap_info *orig_trap)
+static int sbi_trap_emulate_store(struct sbi_trap_regs *regs,
+				  const struct sbi_trap_info *orig_trap,
+				  sbi_trap_st_emulator emu)
 {
 	ulong insn, insn_len;
-	union reg_data val;
+	union sbi_ldst_data val;
 	struct sbi_trap_info uptrap;
-	int i, len = 0;
-
-	sbi_pmu_ctr_incr_fw(SBI_PMU_FW_MISALIGNED_STORE);
+	int rc, len = 0;
 
 	if (orig_trap->tinst & 0x1) {
 		/*
@@ -192,7 +200,9 @@ int sbi_misaligned_store_handler(struct sbi_trap_regs *regs,
 
 	val.data_ulong = GET_RS2(insn, regs);
 
-	if ((insn & INSN_MASK_SW) == INSN_MATCH_SW) {
+	if ((insn & INSN_MASK_SB) == INSN_MATCH_SB) {
+		len = 1;
+	} else if ((insn & INSN_MASK_SW) == INSN_MATCH_SW) {
 		len = 4;
 #if __riscv_xlen == 64
 	} else if ((insn & INSN_MASK_SD) == INSN_MATCH_SD) {
@@ -245,9 +255,26 @@ int sbi_misaligned_store_handler(struct sbi_trap_regs *regs,
 		return sbi_trap_redirect(regs, orig_trap);
 	}
 
-	for (i = 0; i < len; i++) {
-		sbi_store_u8((void *)(orig_trap->tval + i), val.data_bytes[i],
-			     &uptrap);
+	rc = emu(len, val, regs, orig_trap);
+
+	if (rc <= 0)
+		return rc;
+
+	regs->mepc += insn_len;
+
+	return 0;
+}
+
+static int sbi_misaligned_ld_emulator(int rlen, union sbi_ldst_data *out_val,
+				      struct sbi_trap_regs *regs,
+				      const struct sbi_trap_info *orig_trap)
+{
+	struct sbi_trap_info uptrap;
+	int i;
+
+	for (i = 0; i < rlen; i++) {
+		out_val->data_bytes[i] =
+			sbi_load_u8((void *)(orig_trap->tval + i), &uptrap);
 		if (uptrap.cause) {
 			uptrap.epc   = regs->mepc;
 			uptrap.tinst = sbi_misaligned_tinst_fixup(
@@ -255,8 +282,51 @@ int sbi_misaligned_store_handler(struct sbi_trap_regs *regs,
 			return sbi_trap_redirect(regs, &uptrap);
 		}
 	}
-
-	regs->mepc += insn_len;
-
-	return 0;
+	return rlen;
+}
+
+int sbi_misaligned_load_handler(struct sbi_trap_regs *regs,
+				const struct sbi_trap_info *orig_trap)
+{
+	return sbi_trap_emulate_load(regs, orig_trap,
+				     sbi_misaligned_ld_emulator);
+}
+
+static int sbi_misaligned_st_emulator(int wlen, union sbi_ldst_data in_val,
+				      struct sbi_trap_regs *regs,
+				      const struct sbi_trap_info *orig_trap)
+{
+	struct sbi_trap_info uptrap;
+	int i;
+
+	for (i = 0; i < wlen; i++) {
+		sbi_store_u8((void *)(orig_trap->tval + i),
+			     in_val.data_bytes[i], &uptrap);
+		if (uptrap.cause) {
+			uptrap.epc   = regs->mepc;
+			uptrap.tinst = sbi_misaligned_tinst_fixup(
+				orig_trap->tinst, uptrap.tinst, i);
+			return sbi_trap_redirect(regs, &uptrap);
+		}
+	}
+	return wlen;
+}
+
+int sbi_misaligned_store_handler(struct sbi_trap_regs *regs,
+				 const struct sbi_trap_info *orig_trap)
+{
+	return sbi_trap_emulate_store(regs, orig_trap,
+				      sbi_misaligned_st_emulator);
+}
+
+int sbi_load_access_handler(struct sbi_trap_regs *regs,
+			    const struct sbi_trap_info *orig_trap)
+{
+	return sbi_trap_redirect(regs, orig_trap);
+}
+
+int sbi_store_access_handler(struct sbi_trap_regs *regs,
+			     const struct sbi_trap_info *orig_trap)
+{
+	return sbi_trap_redirect(regs, orig_trap);
 }