lib: sbi: Do not override emulator callback for vector load/store

It's wrong to override the emulator callback in sbi_trap_emulate_load/
store. The function must respect the callback function passed in the
parameter. Hence, let the misaligned emulator callback decide when to
use sbi_misaligned_v_ld/st_emulator. To clean up things, also make the
following changes:

- Add the `insn` parameter to the callback. The trapping insn has been
  fetched by the caller already, whether transformed or directly loaded,
  thus saving the trouble in the callback. Note that you must not rely
  on the length of the `insn`, as it can be a transformed one from tinst

- Also the `tcntx` is added, providing the callback with register values
  to handle vector insn or other customized insns.

- Clarify that the read/write length (rlen/wlen) can be 0, in which
  case it could be a vector load/store or some customized instruction.
  The callback is responsible to handle it accordingly.

Also fixed issues in the sbi_misaligned_v_ld/st_emulator:
a. Redirect the trap when OPENSBI_CC_SUPPORT_VECTOR is not available.
b. Ensure the return code is >0 when no faults are redirected.

Fixes: c2acc5e5b0 ("lib: sbi_misaligned_ldst: Add handling of vector load/store")
Signed-off-by: Bo Gan <ganboing@gmail.com>
Reviewed-by: Anup Patel <anup@brainfault.org>
Tested-by: Anirudh Srinivasan <asrinivasan@oss.tenstorrent.com>
Link: https://lore.kernel.org/r/20260605113214.242-6-ganboing@gmail.com
Signed-off-by: Anup Patel <anup@brainfault.org>

include/sbi/sbi_platform.h

@@ -135,12 +135,17 @@ struct sbi_platform_operations {
 				   struct sbi_trap_regs *regs,
 				   struct sbi_ecall_return *out);
 
-	/** platform specific handler to fixup load fault */
+	/** platform specific handler to fixup load fault
-	int (*emulate_load)(int rlen, unsigned long addr,
+	 *  Refer to comments below at sbi_platform_emulate_load */
-			    union sbi_ldst_data *out_val);
+	int (*emulate_load)(ulong insn, int rlen, ulong addr,
-	/** platform specific handler to fixup store fault */
+			    union sbi_ldst_data *out_val,
-	int (*emulate_store)(int wlen, unsigned long addr,
+			    struct sbi_trap_context *tcntx);
-			     union sbi_ldst_data in_val);
+
+	/** platform specific handler to fixup store fault
+	 *  Refer to comments below at sbi_platform_emulate_store */
+	int (*emulate_store)(ulong insn, int wlen, ulong addr,
+			     union sbi_ldst_data in_val,
+			     struct sbi_trap_context *tcntx);
 
 	/** platform specific pmp setup on current HART */
 	void (*pmp_set)(unsigned int n, unsigned long flags,
@@ -619,45 +624,76 @@ static inline int sbi_platform_vendor_ext_provider(
 }
 
 /**
- * Ask platform to emulate the trapped load
+ * Ask platform to emulate the trapped load:
  *
- * @param plat pointer to struct sbi_platform
+ * @param insn the instruction that caused the load fault.
- * @param rlen length of the load: 1/2/4/8...
+ *             It could be a transformed instruction from tinst, thus do
- * @param addr virtual address of the load. Platform needs to page-walk and
+ *             not rely on the length of insn, and use appropriate return
- *        find the physical address if necessary
+ *             code, so the caller can advance mepc properly.
- * @param out_val value loaded
+ * @param rlen read length in [0, 1, 2, 4, 8]. If 0, it's a special load.
+ *             In that case, it could be a vector load or customized insn,
+ *             which may read/gather a block of memory. The emulator should
+ *             further parse the @insn (fetch if 0), and act accordingly.
+ * @param raddr read address. If @rlen is not 0, it's the base address of
+ *              the load. It doesn't necessarily match tcntx->trap->tval,
+ *              in case of unaligned load triggering access fault.
+ *              If @rlen is 0, @raddr should be ignored.
+ * @param out_val the buffer to hold data loaded by the emulator.
+ *                If @rlen == 0, @out_val is ignored by caller.
+ * @param tcntx trap context saved on load fault entry.
  *
- * @return 0 on success and negative error code on failure
+ * @return >0 success: register will be updated by caller if @rlen != 0,
+ *            and mepc will be advanced by caller.
+ *         0  success: no register modification; no mepc advancement.
+ *         <0 failure
+ *
+ * It's expected that if @rlen != 0, and the emulator returns >0, the
+ * caller will set the corresponding registers with @out_val to simplify
+ * things. Otherwise, no register manipulation is done by the caller.
  */
 static inline int sbi_platform_emulate_load(const struct sbi_platform *plat,
-					    int rlen, unsigned long addr,
+					    ulong insn, int rlen, ulong raddr,
-					    union sbi_ldst_data *out_val)
+					    union sbi_ldst_data *out_val,
+					    struct sbi_trap_context *tcntx)
 {
 	if (plat && sbi_platform_ops(plat)->emulate_load) {
-		return sbi_platform_ops(plat)->emulate_load(rlen, addr,
+		return sbi_platform_ops(plat)->emulate_load(insn, rlen, raddr,
-							    out_val);
+							    out_val, tcntx);
 	}
 	return SBI_ENOTSUPP;
 }
 
 /**
- * Ask platform to emulate the trapped store
+ * Ask platform to emulate the trapped store:
  *
- * @param plat pointer to struct sbi_platform
+ * @param insn the instruction that caused the store fault.
- * @param wlen length of the store: 1/2/4/8...
+ *             It could be a transformed instruction from tinst, thus do
- * @param addr virtual address of the store. Platform needs to page-walk and
+ *             not rely on the length of insn, and use appropriate return
- *        find the physical address if necessary
+ *             code, so the caller can advance mepc properly.
- * @param in_val value to store
+ * @param wlen write length in [0, 1, 2, 4, 8]. If 0, it's a special store.
+ *             In that case, it could be a vector store or customized insn,
+ *             which may write/scatter a block of memory. The emulator should
+ *             further parse the @insn (fetch if 0), and act accordingly.
+ * @param waddr write address. If @wlen is not 0, it's the base address of
+ *              the store. It doesn't necessarily match tcntx->trap->tval,
+ *              in case of unaligned store triggering access fault.
+ *              If @wlen is 0, @waddr should be ignored.
+ * @param in_val the buffer to hold data about to be stored by the emulator.
+ *               If @wlen == 0, @in_val should be ignored.
+ * @param tcntx trap context saved on store fault entry.
  *
- * @return 0 on success and negative error code on failure
+ * @return >0 success: mepc will be advanced by caller.
+ *         0  success: no mepc advancement.
+ *         <0 failure
  */
 static inline int sbi_platform_emulate_store(const struct sbi_platform *plat,
-					     int wlen, unsigned long addr,
+					     ulong insn, int wlen, ulong waddr,
-					     union sbi_ldst_data in_val)
+					     union sbi_ldst_data in_val,
+					     struct sbi_trap_context *tcntx)
 {
 	if (plat && sbi_platform_ops(plat)->emulate_store) {
-		return sbi_platform_ops(plat)->emulate_store(wlen, addr,
+		return sbi_platform_ops(plat)->emulate_store(insn, wlen, waddr,
-							     in_val);
+							     in_val, tcntx);
 	}
 	return SBI_ENOTSUPP;
 }

include/sbi/sbi_trap_ldst.h

@@ -31,10 +31,10 @@ int sbi_store_access_handler(struct sbi_trap_context *tcntx);
 ulong sbi_misaligned_tinst_fixup(ulong orig_tinst, ulong new_tinst,
 				 ulong addr_offset);
 
-int sbi_misaligned_v_ld_emulator(int rlen, union sbi_ldst_data *out_val,
+int sbi_misaligned_v_ld_emulator(ulong insn,
 				 struct sbi_trap_context *tcntx);
 
-int sbi_misaligned_v_st_emulator(int wlen, union sbi_ldst_data in_val,
+int sbi_misaligned_v_st_emulator(ulong insn,
 				 struct sbi_trap_context *tcntx);
 
 #endif

lib/sbi/sbi_trap_ldst.c

@@ -18,18 +18,18 @@
 
 /**
  * Load emulator callback:
- *
+ *   Refer to comments of `sbi_platform_emulate_load`.
- * @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,
+typedef int (*sbi_trap_ld_emulator)(ulong insn, int rlen, ulong raddr,
+				    union sbi_ldst_data *out_val,
 				    struct sbi_trap_context *tcntx);
 
 /**
  * Store emulator callback:
- *
+ *   Refer to comments of `sbi_platform_emulate_store`.
- * @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,
+typedef int (*sbi_trap_st_emulator)(ulong insn, int wlen, ulong waddr,
+				    union sbi_ldst_data in_val,
 				    struct sbi_trap_context *tcntx);
 
 ulong sbi_misaligned_tinst_fixup(ulong orig_tinst, ulong new_tinst,
@@ -52,7 +52,7 @@ static int sbi_trap_emulate_load(struct sbi_trap_context *tcntx,
 	ulong insn, insn_len;
 	union sbi_ldst_data val = { 0 };
 	struct sbi_trap_info uptrap;
-	int rc, fp = 0, shift = 0, len = 0, vector = 0;
+	int rc, fp = 0, shift = 0, len = 0;
 
 	if (orig_trap->tinst & 0x1) {
 		/*
@@ -144,18 +144,14 @@ static int sbi_trap_emulate_load(struct sbi_trap_context *tcntx,
 		len = 2;
 		shift = 8 * (sizeof(ulong) - len);
 		insn = RVC_RS2S(insn) << SH_RD;
-	} else if (IS_VECTOR_LOAD_STORE(insn)) {
-		vector = 1;
-		emu = sbi_misaligned_v_ld_emulator;
-	} else {
-		return sbi_trap_redirect(regs, orig_trap);
 	}
 
-	rc = emu(len, &val, tcntx);
+	rc = emu(insn, len, orig_trap->tval, &val, tcntx);
 	if (rc <= 0)
 		return rc;
+	if (!len)
+		goto epc_fixup;
 
-	if (!vector) {
 	if (!fp)
 		SET_RD(insn, regs, ((long)(val.data_ulong << shift)) >> shift);
 #ifdef __riscv_flen
@@ -164,8 +160,8 @@ static int sbi_trap_emulate_load(struct sbi_trap_context *tcntx,
 	else
 		SET_F32_RD(insn, regs, val.data_ulong);
 #endif
-	}
 
+epc_fixup:
 	regs->mepc += insn_len;
 
 	return 0;
@@ -253,13 +249,9 @@ static int sbi_trap_emulate_store(struct sbi_trap_context *tcntx,
 	} else if ((insn & INSN_MASK_C_SH) == INSN_MATCH_C_SH) {
 		len		= 2;
 		val.data_ulong = GET_RS2S(insn, regs);
-	} else if (IS_VECTOR_LOAD_STORE(insn)) {
-		emu = sbi_misaligned_v_st_emulator;
-	} else {
-		return sbi_trap_redirect(regs, orig_trap);
 	}
 
-	rc = emu(len, val, tcntx);
+	rc = emu(insn, len, orig_trap->tval, val, tcntx);
 	if (rc <= 0)
 		return rc;
 
@@ -268,7 +260,8 @@ static int sbi_trap_emulate_store(struct sbi_trap_context *tcntx,
 	return 0;
 }
 
-static int sbi_misaligned_ld_emulator(int rlen, union sbi_ldst_data *out_val,
+static int sbi_misaligned_ld_emulator(ulong insn, int rlen, ulong addr,
+				      union sbi_ldst_data *out_val,
 				      struct sbi_trap_context *tcntx)
 {
 	const struct sbi_trap_info *orig_trap = &tcntx->trap;
@@ -276,9 +269,20 @@ static int sbi_misaligned_ld_emulator(int rlen, union sbi_ldst_data *out_val,
 	struct sbi_trap_info uptrap;
 	int i;
 
+	if (!rlen) {
+		if (IS_VECTOR_LOAD_STORE(insn))
+			return sbi_misaligned_v_ld_emulator(insn, tcntx);
+		else
+			/* Unrecognized instruction. Can't emulate it. */
+			return sbi_trap_redirect(regs, orig_trap);
+	}
+	/* For misaligned fault, addr must be the same as orig_trap->tval */
+	if (addr != orig_trap->tval)
+		return SBI_EFAIL;
+
 	for (i = 0; i < rlen; i++) {
 		out_val->data_bytes[i] =
-			sbi_load_u8((void *)(orig_trap->tval + i), &uptrap);
+			sbi_load_u8((void *)(addr + i), &uptrap);
 		if (uptrap.cause) {
 			uptrap.tinst = sbi_misaligned_tinst_fixup(
 				orig_trap->tinst, uptrap.tinst, i);
@@ -293,7 +297,8 @@ int sbi_misaligned_load_handler(struct sbi_trap_context *tcntx)
 	return sbi_trap_emulate_load(tcntx, sbi_misaligned_ld_emulator);
 }
 
-static int sbi_misaligned_st_emulator(int wlen, union sbi_ldst_data in_val,
+static int sbi_misaligned_st_emulator(ulong insn, int wlen, ulong addr,
+				      union sbi_ldst_data in_val,
 				      struct sbi_trap_context *tcntx)
 {
 	const struct sbi_trap_info *orig_trap = &tcntx->trap;
@@ -301,8 +306,19 @@ static int sbi_misaligned_st_emulator(int wlen, union sbi_ldst_data in_val,
 	struct sbi_trap_info uptrap;
 	int i;
 
+	if (!wlen) {
+		if (IS_VECTOR_LOAD_STORE(insn))
+			return sbi_misaligned_v_st_emulator(insn, tcntx);
+		else
+			/* Unrecognized instruction. Can't emulate it. */
+			return sbi_trap_redirect(regs, orig_trap);
+	}
+	/* For misaligned fault, addr must be the same as orig_trap->tval */
+	if (addr != orig_trap->tval)
+		return SBI_EFAIL;
+
 	for (i = 0; i < wlen; i++) {
-		sbi_store_u8((void *)(orig_trap->tval + i),
+		sbi_store_u8((void *)(addr + i),
 			     in_val.data_bytes[i], &uptrap);
 		if (uptrap.cause) {
 			uptrap.tinst = sbi_misaligned_tinst_fixup(
@@ -318,22 +334,26 @@ int sbi_misaligned_store_handler(struct sbi_trap_context *tcntx)
 	return sbi_trap_emulate_store(tcntx, sbi_misaligned_st_emulator);
 }
 
-static int sbi_ld_access_emulator(int rlen, union sbi_ldst_data *out_val,
+static int sbi_ld_access_emulator(ulong insn, int rlen, ulong addr,
+				  union sbi_ldst_data *out_val,
 				  struct sbi_trap_context *tcntx)
 {
 	const struct sbi_trap_info *orig_trap = &tcntx->trap;
 	struct sbi_trap_regs *regs = &tcntx->regs;
+	int rc;
 
 	/* If fault came from M mode, just fail */
 	if (sbi_mstatus_prev_mode(regs->mstatus) == PRV_M)
 		return SBI_EINVAL;
 
+	rc = sbi_platform_emulate_load(sbi_platform_thishart_ptr(),
+				       insn, rlen, addr, out_val, tcntx);
+
 	/* If platform emulator failed, we redirect instead of fail */
-	if (sbi_platform_emulate_load(sbi_platform_thishart_ptr(), rlen,
+	if (rc < 0)
-				      orig_trap->tval, out_val))
 		return sbi_trap_redirect(regs, orig_trap);
 
-	return rlen;
+	return rc;
 }
 
 int sbi_load_access_handler(struct sbi_trap_context *tcntx)
@@ -341,22 +361,26 @@ int sbi_load_access_handler(struct sbi_trap_context *tcntx)
 	return sbi_trap_emulate_load(tcntx, sbi_ld_access_emulator);
 }
 
-static int sbi_st_access_emulator(int wlen, union sbi_ldst_data in_val,
+static int sbi_st_access_emulator(ulong insn, int wlen, ulong addr,
+				  union sbi_ldst_data in_val,
 				  struct sbi_trap_context *tcntx)
 {
 	const struct sbi_trap_info *orig_trap = &tcntx->trap;
 	struct sbi_trap_regs *regs = &tcntx->regs;
+	int rc;
 
 	/* If fault came from M mode, just fail */
 	if (sbi_mstatus_prev_mode(regs->mstatus) == PRV_M)
 		return SBI_EINVAL;
 
+	rc = sbi_platform_emulate_store(sbi_platform_thishart_ptr(),
+					insn, wlen, addr, in_val, tcntx);
+
 	/* If platform emulator failed, we redirect instead of fail */
-	if (sbi_platform_emulate_store(sbi_platform_thishart_ptr(), wlen,
+	if (rc < 0)
-				       orig_trap->tval, in_val))
 		return sbi_trap_redirect(regs, orig_trap);
 
-	return wlen;
+	return rc;
 }
 
 int sbi_store_access_handler(struct sbi_trap_context *tcntx)

lib/sbi/sbi_trap_v_ldst.c

@@ -137,13 +137,11 @@ static inline void vsetvl(ulong vl, ulong vtype)
 			:: "r" (vl), "r" (vtype));
 }
 
-int sbi_misaligned_v_ld_emulator(int rlen, union sbi_ldst_data *out_val,
+int sbi_misaligned_v_ld_emulator(ulong insn, struct sbi_trap_context *tcntx)
-				 struct sbi_trap_context *tcntx)
 {
 	const struct sbi_trap_info *orig_trap = &tcntx->trap;
 	struct sbi_trap_regs *regs = &tcntx->regs;
 	struct sbi_trap_info uptrap;
-	ulong insn = sbi_get_insn(regs->mepc, &uptrap);
 	ulong vl = csr_read(CSR_VL);
 	ulong vtype = csr_read(CSR_VTYPE);
 	ulong vlenb = csr_read(CSR_VLENB);
@@ -234,16 +232,15 @@ int sbi_misaligned_v_ld_emulator(int rlen, union sbi_ldst_data *out_val,
 	/* restore clobbered vl/vtype */
 	vsetvl(vl, vtype);
 
-	return vl;
+	/* Return a >0 value for the caller to advance mepc */
+	return 1;
 }
 
-int sbi_misaligned_v_st_emulator(int wlen, union sbi_ldst_data in_val,
+int sbi_misaligned_v_st_emulator(ulong insn, struct sbi_trap_context *tcntx)
-				 struct sbi_trap_context *tcntx)
 {
 	const struct sbi_trap_info *orig_trap = &tcntx->trap;
 	struct sbi_trap_regs *regs = &tcntx->regs;
 	struct sbi_trap_info uptrap;
-	ulong insn = sbi_get_insn(regs->mepc, &uptrap);
 	ulong vl = csr_read(CSR_VL);
 	ulong vtype = csr_read(CSR_VTYPE);
 	ulong vlenb = csr_read(CSR_VLENB);
@@ -328,17 +325,17 @@ int sbi_misaligned_v_st_emulator(int wlen, union sbi_ldst_data in_val,
 	/* restore clobbered vl/vtype */
 	vsetvl(vl, vtype);
 
-	return vl;
+	/* Return a >0 value for the caller to advance mepc */
+	return 1;
 }
 #else
-int sbi_misaligned_v_ld_emulator(int rlen, union sbi_ldst_data *out_val,
+int sbi_misaligned_v_ld_emulator(ulong insn, struct sbi_trap_context *tcntx)
-				 struct sbi_trap_context *tcntx)
 {
 	/* Unable to emulate, send trap to previous mode. */
 	return sbi_trap_redirect(&tcntx->regs, &tcntx->trap);
 }
-int sbi_misaligned_v_st_emulator(int wlen, union sbi_ldst_data in_val,
+
-				 struct sbi_trap_context *tcntx)
+int sbi_misaligned_v_st_emulator(ulong insn, struct sbi_trap_context *tcntx)
 {
 	/* Unable to emulate, send trap to previous mode. */
 	return sbi_trap_redirect(&tcntx->regs, &tcntx->trap);