lib: sbi: Introduce sbi_trap_exit() API

We introduce sbi_trap_exit() API which can help non-firmware
(i.e. generic or platform) code to force exit trap/interrupt
handling and resume execution at context pointed by parameter
"const struct sbi_trap_regs *regs".

This new sbi_trap_exit() API will help Keystone Enclave project
to resume execution of enclave from custom SBI call handler.

Signed-off-by: Anup Patel <anup.patel@wdc.com>
Reviewed-by: Atish Patra <atish.patra@wdc.com>

diff --git a/firmware/fw_base.S b/firmware/fw_base.S
index fb504e8..ab33e11 100644 (file)
--- a/firmware/fw_base.S
+++ b/firmware/fw_base.S
@@ -261,6 +261,9 @@ _scratch_init:
        /* Store hartid-to-scratch function address in scratch space */
        la      a4, _hartid_to_scratch
        REG_S   a4, SBI_SCRATCH_HARTID_TO_SCRATCH_OFFSET(tp)
+       /* Store trap-exit function address in scratch space */
+       la      a4, _trap_exit
+       REG_S   a4, SBI_SCRATCH_TRAP_EXIT_OFFSET(tp)
        /* Clear tmp0 in scratch space */
        REG_S   zero, SBI_SCRATCH_TMP0_OFFSET(tp)
        /* Store firmware options in scratch space */
@@ -423,6 +426,18 @@ _skip_trap_handler_rv32_hyp:
 #endif
        csrw    CSR_MTVEC, a4
 
+#if __riscv_xlen == 32
+       /* Override trap exit for H-extension */
+       csrr    a5, CSR_MISA
+       srli    a5, a5, ('H' - 'A')
+       andi    a5, a5, 0x1
+       beq     a5, zero, _skip_trap_exit_rv32_hyp
+       la      a4, _trap_exit_rv32_hyp
+       csrr    a5, CSR_MSCRATCH
+       REG_S   a4, SBI_SCRATCH_TRAP_EXIT_OFFSET(a5)
+_skip_trap_exit_rv32_hyp:
+#endif
+
        /* Initialize SBI runtime */
        csrr    a0, CSR_MSCRATCH
        call    sbi_init
@@ -653,6 +668,20 @@ _trap_handler:
 
        mret
 
+       .section .entry, "ax", %progbits
+       .align 3
+       .globl _trap_exit
+_trap_exit:
+       add     sp, a0, zero
+
+       TRAP_RESTORE_GENERAL_REGS_EXCEPT_SP_T0
+
+       TRAP_RESTORE_MEPC_MSTATUS 0
+
+       TRAP_RESTORE_SP_T0
+
+       mret
+
 #if __riscv_xlen == 32
        .section .entry, "ax", %progbits
        .align 3
@@ -673,6 +702,20 @@ _trap_handler_rv32_hyp:
        TRAP_RESTORE_SP_T0
 
        mret
+
+       .section .entry, "ax", %progbits
+       .align 3
+       .globl _trap_exit_rv32_hyp
+_trap_exit_rv32_hyp:
+       add     sp, a0, zero
+
+       TRAP_RESTORE_GENERAL_REGS_EXCEPT_SP_T0
+
+       TRAP_RESTORE_MEPC_MSTATUS 1
+
+       TRAP_RESTORE_SP_T0
+
+       mret
 #endif
 
        .section .entry, "ax", %progbits

diff --git a/include/sbi/sbi_scratch.h b/include/sbi/sbi_scratch.h
index 9f3453d..e7079f5 100644 (file)
--- a/include/sbi/sbi_scratch.h
+++ b/include/sbi/sbi_scratch.h
@@ -30,12 +30,14 @@
 #define SBI_SCRATCH_PLATFORM_ADDR_OFFSET       (6 * __SIZEOF_POINTER__)
 /** Offset of hartid_to_scratch member in sbi_scratch */
 #define SBI_SCRATCH_HARTID_TO_SCRATCH_OFFSET   (7 * __SIZEOF_POINTER__)
+/** Offset of trap_exit member in sbi_scratch */
+#define SBI_SCRATCH_TRAP_EXIT_OFFSET           (8 * __SIZEOF_POINTER__)
 /** Offset of tmp0 member in sbi_scratch */
-#define SBI_SCRATCH_TMP0_OFFSET                        (8 * __SIZEOF_POINTER__)
+#define SBI_SCRATCH_TMP0_OFFSET                        (9 * __SIZEOF_POINTER__)
 /** Offset of options member in sbi_scratch */
-#define SBI_SCRATCH_OPTIONS_OFFSET             (9 * __SIZEOF_POINTER__)
+#define SBI_SCRATCH_OPTIONS_OFFSET             (10 * __SIZEOF_POINTER__)
 /** Offset of extra space in sbi_scratch */
-#define SBI_SCRATCH_EXTRA_SPACE_OFFSET         (10 * __SIZEOF_POINTER__)
+#define SBI_SCRATCH_EXTRA_SPACE_OFFSET         (11 * __SIZEOF_POINTER__)
 /** Maximum size of sbi_scratch (4KB) */
 #define SBI_SCRATCH_SIZE                       (0x1000)
 
@@ -63,6 +65,8 @@ struct sbi_scratch {
        unsigned long platform_addr;
        /** Address of HART ID to sbi_scratch conversion function */
        unsigned long hartid_to_scratch;
+       /** Address of trap exit function */
+       unsigned long trap_exit;
        /** Temporary storage */
        unsigned long tmp0;
        /** Options for OpenSBI library */

diff --git a/include/sbi/sbi_trap.h b/include/sbi/sbi_trap.h
index 5d0962f..04001df 100644 (file)
--- a/include/sbi/sbi_trap.h
+++ b/include/sbi/sbi_trap.h
@@ -207,6 +207,8 @@ int sbi_trap_redirect(struct sbi_trap_regs *regs,
 
 void sbi_trap_handler(struct sbi_trap_regs *regs);
 
+void __noreturn sbi_trap_exit(const struct sbi_trap_regs *regs);
+
 #endif
 
 #endif

diff --git a/lib/sbi/sbi_trap.c b/lib/sbi/sbi_trap.c
index db5aa2f..b7349d2 100644 (file)
--- a/lib/sbi/sbi_trap.c
+++ b/lib/sbi/sbi_trap.c
@@ -16,6 +16,7 @@
 #include <sbi/sbi_illegal_insn.h>
 #include <sbi/sbi_ipi.h>
 #include <sbi/sbi_misaligned_ldst.h>
+#include <sbi/sbi_scratch.h>
 #include <sbi/sbi_timer.h>
 #include <sbi/sbi_trap.h>
 
@@ -271,3 +272,22 @@ trap_error:
        if (rc)
                sbi_trap_error(msg, rc, mcause, mtval, mtval2, mtinst, regs);
 }
+
+typedef void (*trap_exit_t)(const struct sbi_trap_regs *regs);
+
+/**
+ * Exit trap/interrupt handling
+ *
+ * This function is called by non-firmware code to abruptly exit
+ * trap/interrupt handling and resume execution at context pointed
+ * by given register state.
+ *
+ * @param regs pointer to register state
+ */
+void __noreturn sbi_trap_exit(const struct sbi_trap_regs *regs)
+{
+       struct sbi_scratch *scratch = sbi_scratch_thishart_ptr();
+
+       ((trap_exit_t)scratch->trap_exit)(regs);
+       __builtin_unreachable();
+}