lib: sbi: Introduce trap context

Club the struct sbi_trap_regs and struct sbi_trap_info a new
struct sbi_trap_context (aka trap context) which must be saved
by low-level trap handler before calling sbi_trap_handler().

To track nested traps, the struct sbi_scratch points to the current
trap context and the trap context has pointer to pervious context
of previous trap.

Signed-off-by: Anup Patel <apatel@ventanamicro.com>
Reviewed-by: Samuel Holland <samuel.holland@sifive.com>
Tested-by: Samuel Holland <samuel.holland@sifive.com>

3 files changed, 103 insertions, 46 deletions

diff --git a/firmware/fw_base.S b/firmware/fw_base.S
index 539fd1d..6290322 100644
--- a/firmware/fw_base.S
+++ b/firmware/fw_base.S
@@ -446,14 +446,12 @@ _start_warm:
 
 	/* Setup trap handler */
 	lla	a4, _trap_handler
-#if __riscv_xlen == 32
 	csrr	a5, CSR_MISA
 	srli	a5, a5, ('H' - 'A')
 	andi	a5, a5, 0x1
-	beq	a5, zero, _skip_trap_handler_rv32_hyp
-	lla	a4, _trap_handler_rv32_hyp
-_skip_trap_handler_rv32_hyp:
-#endif
+	beq	a5, zero, _skip_trap_handler_hyp
+	lla	a4, _trap_handler_hyp
+_skip_trap_handler_hyp:
 	csrw	CSR_MTVEC, a4
 
 	/* Initialize SBI runtime */
@@ -564,10 +562,10 @@ memcmp:
 	xor	t0, tp, t0
 
 	/* Save original SP on exception stack */
-	REG_S	sp, (SBI_TRAP_REGS_OFFSET(sp) - SBI_TRAP_REGS_SIZE)(t0)
+	REG_S	sp, (SBI_TRAP_REGS_OFFSET(sp) - SBI_TRAP_CONTEXT_SIZE)(t0)
 
-	/* Set SP to exception stack and make room for trap registers */
-	add	sp, t0, -(SBI_TRAP_REGS_SIZE)
+	/* Set SP to exception stack and make room for trap context */
+	add	sp, t0, -(SBI_TRAP_CONTEXT_SIZE)
 
 	/* Restore T0 from scratch space */
 	REG_L	t0, SBI_SCRATCH_TMP0_OFFSET(tp)
@@ -627,6 +625,32 @@ memcmp:
 	REG_S	t6, SBI_TRAP_REGS_OFFSET(t6)(sp)
 .endm
 
+.macro	TRAP_SAVE_INFO have_mstatush have_h_extension
+	csrr	t0, CSR_MCAUSE
+	REG_S	t0, (SBI_TRAP_REGS_SIZE + SBI_TRAP_INFO_OFFSET(cause))(sp)
+	csrr	t0, CSR_MTVAL
+	REG_S	t0, (SBI_TRAP_REGS_SIZE + SBI_TRAP_INFO_OFFSET(tval))(sp)
+.if \have_h_extension
+	csrr	t0, CSR_MTVAL2
+	REG_S	t0, (SBI_TRAP_REGS_SIZE + SBI_TRAP_INFO_OFFSET(tval2))(sp)
+	csrr	t0, CSR_MTINST
+	REG_S	t0, (SBI_TRAP_REGS_SIZE + SBI_TRAP_INFO_OFFSET(tinst))(sp)
+	.if \have_mstatush
+	csrr	t0, CSR_MSTATUSH
+	srli	t0, t0, MSTATUSH_GVA_SHIFT
+	.else
+	csrr	t0, CSR_MSTATUS
+	srli	t0, t0, MSTATUS_GVA_SHIFT
+	.endif
+	and	t0, t0, 0x1
+.else
+	REG_S	zero, (SBI_TRAP_REGS_SIZE + SBI_TRAP_INFO_OFFSET(tval2))(sp)
+	REG_S	zero, (SBI_TRAP_REGS_SIZE + SBI_TRAP_INFO_OFFSET(tinst))(sp)
+	li	t0, 0
+.endif
+	REG_S	t0, (SBI_TRAP_REGS_SIZE + SBI_TRAP_INFO_OFFSET(gva))(sp)
+.endm
+
 .macro	TRAP_CALL_C_ROUTINE
 	/* Call C routine */
 	add	a0, sp, zero
@@ -696,6 +720,8 @@ _trap_handler:
 
 	TRAP_SAVE_GENERAL_REGS_EXCEPT_SP_T0
 
+	TRAP_SAVE_INFO 0 0
+
 	TRAP_CALL_C_ROUTINE
 
 	TRAP_RESTORE_GENERAL_REGS_EXCEPT_A0_T0
@@ -706,27 +732,39 @@ _trap_handler:
 
 	mret
 
-#if __riscv_xlen == 32
 	.section .entry, "ax", %progbits
 	.align 3
-	.globl _trap_handler_rv32_hyp
-_trap_handler_rv32_hyp:
+	.globl _trap_handler_hyp
+_trap_handler_hyp:
 	TRAP_SAVE_AND_SETUP_SP_T0
 
+#if __riscv_xlen == 32
 	TRAP_SAVE_MEPC_MSTATUS 1
+#else
+	TRAP_SAVE_MEPC_MSTATUS 0
+#endif
 
 	TRAP_SAVE_GENERAL_REGS_EXCEPT_SP_T0
 
+#if __riscv_xlen == 32
+	TRAP_SAVE_INFO 1 1
+#else
+	TRAP_SAVE_INFO 0 1
+#endif
+
 	TRAP_CALL_C_ROUTINE
 
 	TRAP_RESTORE_GENERAL_REGS_EXCEPT_A0_T0
 
+#if __riscv_xlen == 32
 	TRAP_RESTORE_MEPC_MSTATUS 1
+#else
+	TRAP_RESTORE_MEPC_MSTATUS 0
+#endif
 
 	TRAP_RESTORE_A0_T0
 
 	mret
-#endif
 
 	.section .entry, "ax", %progbits
 	.align 3
diff --git a/include/sbi/sbi_trap.h b/include/sbi/sbi_trap.h
index a6032ab..f7c170e 100644
--- a/include/sbi/sbi_trap.h
+++ b/include/sbi/sbi_trap.h
@@ -112,9 +112,15 @@
 /** Size (in bytes) of sbi_trap_info */
 #define SBI_TRAP_INFO_SIZE SBI_TRAP_INFO_OFFSET(last)
 
+/** Size (in bytes) of sbi_trap_context */
+#define SBI_TRAP_CONTEXT_SIZE (SBI_TRAP_REGS_SIZE + \
+			       SBI_TRAP_INFO_SIZE + \
+			       __SIZEOF_POINTER__)
+
 #ifndef __ASSEMBLER__
 
 #include <sbi/sbi_types.h>
+#include <sbi/sbi_scratch.h>
 
 /** Representation of register state at time of trap/interrupt */
 struct sbi_trap_regs {
@@ -204,6 +210,16 @@ struct sbi_trap_info {
 	unsigned long gva;
 };
 
+/** Representation of trap context saved on stack */
+struct sbi_trap_context {
+	/** Register state */
+	struct sbi_trap_regs regs;
+	/** Trap details */
+	struct sbi_trap_info trap;
+	/** Pointer to previous trap context */
+	struct sbi_trap_context *prev_context;
+};
+
 static inline unsigned long sbi_regs_gva(const struct sbi_trap_regs *regs)
 {
 	/*
@@ -223,7 +239,18 @@ static inline unsigned long sbi_regs_gva(const struct sbi_trap_regs *regs)
 int sbi_trap_redirect(struct sbi_trap_regs *regs,
 		      const struct sbi_trap_info *trap);
 
-struct sbi_trap_regs *sbi_trap_handler(struct sbi_trap_regs *regs);
+static inline struct sbi_trap_context *sbi_trap_get_context(struct sbi_scratch *scratch)
+{
+	return (scratch) ? (void *)scratch->trap_context : NULL;
+}
+
+static inline void sbi_trap_set_context(struct sbi_scratch *scratch,
+					struct sbi_trap_context *tcntx)
+{
+	scratch->trap_context = (unsigned long)tcntx;
+}
+
+struct sbi_trap_context *sbi_trap_handler(struct sbi_trap_context *tcntx);
 
 #endif
 
diff --git a/lib/sbi/sbi_trap.c b/lib/sbi/sbi_trap.c
index b059c4b..4dbda06 100644
--- a/lib/sbi/sbi_trap.c
+++ b/lib/sbi/sbi_trap.c
@@ -24,18 +24,18 @@
 #include <sbi/sbi_trap.h>
 
 static void __noreturn sbi_trap_error(const char *msg, int rc,
-				      ulong mcause, ulong mtval, ulong mtval2,
-				      ulong mtinst, struct sbi_trap_regs *regs)
+				      const struct sbi_trap_info *trap,
+				      const struct sbi_trap_regs *regs)
 {
 	u32 hartid = current_hartid();
 
 	sbi_printf("%s: hart%d: %s (error %d)\n", __func__, hartid, msg, rc);
 	sbi_printf("%s: hart%d: mcause=0x%" PRILX " mtval=0x%" PRILX "\n",
-		   __func__, hartid, mcause, mtval);
+		   __func__, hartid, trap->cause, trap->tval);
 	if (misa_extension('H')) {
 		sbi_printf("%s: hart%d: mtval2=0x%" PRILX
 			   " mtinst=0x%" PRILX "\n",
-			   __func__, hartid, mtval2, mtinst);
+			   __func__, hartid, trap->tval2, trap->tinst);
 	}
 	sbi_printf("%s: hart%d: mepc=0x%" PRILX " mstatus=0x%" PRILX "\n",
 		   __func__, hartid, regs->mepc, regs->mstatus);
@@ -258,20 +258,20 @@ static int sbi_trap_aia_irq(struct sbi_trap_regs *regs, ulong mcause)
  * 6. Stack pointer (SP) is setup for current HART
  * 7. Interrupts are disabled in MSTATUS CSR
  *
- * @param regs pointer to register state
+ * @param tcntx pointer to trap context
  */
-struct sbi_trap_regs *sbi_trap_handler(struct sbi_trap_regs *regs)
+struct sbi_trap_context *sbi_trap_handler(struct sbi_trap_context *tcntx)
 {
 	int rc = SBI_ENOTSUPP;
 	const char *msg = "trap handler failed";
-	ulong mcause = csr_read(CSR_MCAUSE);
-	ulong mtval = csr_read(CSR_MTVAL), mtval2 = 0, mtinst = 0;
-	struct sbi_trap_info trap;
+	struct sbi_scratch *scratch = sbi_scratch_thishart_ptr();
+	const struct sbi_trap_info *trap = &tcntx->trap;
+	struct sbi_trap_regs *regs = &tcntx->regs;
+	ulong mcause = tcntx->trap.cause;
 
-	if (misa_extension('H')) {
-		mtval2 = csr_read(CSR_MTVAL2);
-		mtinst = csr_read(CSR_MTINST);
-	}
+	/* Update trap context pointer */
+	tcntx->prev_context = sbi_trap_get_context(scratch);
+	sbi_trap_set_context(scratch, tcntx);
 
 	if (mcause & (1UL << (__riscv_xlen - 1))) {
 		if (sbi_hart_has_extension(sbi_scratch_thishart_ptr(),
@@ -279,32 +279,23 @@ struct sbi_trap_regs *sbi_trap_handler(struct sbi_trap_regs *regs)
 			rc = sbi_trap_aia_irq(regs, mcause);
 		else
 			rc = sbi_trap_nonaia_irq(regs, mcause);
-		if (rc) {
-			msg = "unhandled local interrupt";
-			goto trap_error;
-		}
-		return regs;
+		msg = "unhandled local interrupt";
+		goto trap_done;
 	}
-	/* Original trap_info */
-	trap.cause = mcause;
-	trap.tval  = mtval;
-	trap.tval2 = mtval2;
-	trap.tinst = mtinst;
-	trap.gva   = sbi_regs_gva(regs);
 
 	switch (mcause) {
 	case CAUSE_ILLEGAL_INSTRUCTION:
-		rc  = sbi_illegal_insn_handler(mtval, regs);
+		rc  = sbi_illegal_insn_handler(tcntx->trap.tval, 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);
+		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);
+		rc  = sbi_misaligned_store_handler(regs, trap);
 		msg = "misaligned store handler failed";
 		break;
 	case CAUSE_SUPERVISOR_ECALL:
@@ -314,23 +305,24 @@ struct sbi_trap_regs *sbi_trap_handler(struct sbi_trap_regs *regs)
 		break;
 	case CAUSE_LOAD_ACCESS:
 		sbi_pmu_ctr_incr_fw(SBI_PMU_FW_ACCESS_LOAD);
-		rc  = sbi_load_access_handler(regs, &trap);
+		rc  = sbi_load_access_handler(regs, trap);
 		msg = "load fault handler failed";
 		break;
 	case CAUSE_STORE_ACCESS:
 		sbi_pmu_ctr_incr_fw(SBI_PMU_FW_ACCESS_STORE);
-		rc  = sbi_store_access_handler(regs, &trap);
+		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";
-		rc  = sbi_trap_redirect(regs, &trap);
+		rc  = sbi_trap_redirect(regs, trap);
 		break;
 	}
 
-trap_error:
+trap_done:
 	if (rc)
-		sbi_trap_error(msg, rc, mcause, mtval, mtval2, mtinst, regs);
-	return regs;
+		sbi_trap_error(msg, rc, trap, regs);
+	sbi_trap_set_context(scratch, tcntx->prev_context);
+	return tcntx;
 }