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lib: sbi: Introduce sbi_trap_exit() API

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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>
This commit is contained in:
Anup Patel 2020-12-29 11:39:22 +05:30 • committed by Anup Patel
parent 80bc5065bb
commit b7df5e4392
4 changed files with 72 additions and 3 deletions
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43
firmware/fw_base.S
View file

@ -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

10
include/sbi/sbi_scratch.h
View file

@ -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 */

2
include/sbi/sbi_trap.h
View file

@ -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

20
lib/sbi/sbi_trap.c
View file

@ -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();
}