| Message ID | 20240913143419.3258868-7-cleger@rivosinc.com |
|---|---|
| State | Superseded |
| Headers | show |
| Series | lib: sbi: add Ssdbltrp and Smdbltrp ISA extensions | expand |
On 2024-09-13 9:34 AM, Clément Léger wrote: > Add support for the Smdbltrp[1] ISA extension. First thing to do is > clearing MDT on entry after setting the first MTVEC (since MDT is > reset to 1). Additionally, during trap handling, clear MDT once all > critical CSRs have been saved and in return path, restore MSTATUS before > restoring MEPC to avoid taking another trap which would clobber it. > > Link: https://github.com/riscv/riscv-double-trap/releases/download/v0.56/riscv-double-trap.pdf [1] > Signed-off-by: Clément Léger <cleger@rivosinc.com> > --- > firmware/fw_base.S | 33 ++++++++++++++++++++++++++++++--- > include/sbi/riscv_encoding.h | 2 ++ > 2 files changed, 32 insertions(+), 3 deletions(-) I didn't see you had sent v2 until after replying to the other thread. This looks good to me! Reviewed-by: Samuel Holland <samuel.holland@sifive.com> > > diff --git a/firmware/fw_base.S b/firmware/fw_base.S > index b950c0b..3703cd6 100644 > --- a/firmware/fw_base.S > +++ b/firmware/fw_base.S > @@ -31,6 +31,16 @@ > add \__d4, \__s4, zero > .endm > > +.macro CLEAR_MDT tmp > +#if __riscv_xlen == 32 > + li \tmp, MSTATUSH_MDT > + csrc CSR_MSTATUSH, \tmp > +#else > + li \tmp, MSTATUS_MDT > + csrc CSR_MSTATUS, \tmp > +#endif > +.endm > + > .section .entry, "ax", %progbits > .align 3 > .globl _start > @@ -91,6 +101,14 @@ _bss_zero: > lla s4, _start_hang > csrw CSR_MTVEC, s4 > > + /* > + * While at this point, trap handling is rudimentary, if a trap happens, > + * it will end up in _start_hang which is enough to hook up a GDB. Clear > + * MDT to avoid generating a double trap and thus entering a > + * critical-error state. > + */ > + CLEAR_MDT t0 > + > /* Setup temporary stack */ > lla s4, _fw_end > li s5, (SBI_SCRATCH_SIZE * 2) > @@ -362,6 +380,9 @@ _start_warm: > _skip_trap_handler_hyp: > csrw CSR_MTVEC, a4 > > + /* Clear MDT here again for all harts */ > + CLEAR_MDT t0 > + > /* Initialize SBI runtime */ > csrr a0, CSR_MSCRATCH > call sbi_init > @@ -557,6 +578,9 @@ memcmp: > li t0, 0 > .endif > REG_S t0, (SBI_TRAP_REGS_SIZE + SBI_TRAP_INFO_OFFSET(gva))(sp) > + > + /* We are ready to take another trap, clear MDT */ > + CLEAR_MDT t0 > .endm > > .macro TRAP_CALL_C_ROUTINE > @@ -599,15 +623,18 @@ memcmp: > .endm > > .macro TRAP_RESTORE_MEPC_MSTATUS have_mstatush > - /* Restore MEPC and MSTATUS CSRs */ > - REG_L t0, SBI_TRAP_REGS_OFFSET(mepc)(a0) > - csrw CSR_MEPC, t0 > + /* > + * Restore MSTATUS and MEPC CSRs starting with MSTATUS to set MDT > + * flags since we can not take a trap now or MEPC would be cloberred > + */ > REG_L t0, SBI_TRAP_REGS_OFFSET(mstatus)(a0) > csrw CSR_MSTATUS, t0 > .if \have_mstatush > REG_L t0, SBI_TRAP_REGS_OFFSET(mstatusH)(a0) > csrw CSR_MSTATUSH, t0 > .endif > + REG_L t0, SBI_TRAP_REGS_OFFSET(mepc)(a0) > + csrw CSR_MEPC, t0 > .endm > > .macro TRAP_RESTORE_A0_T0 > diff --git a/include/sbi/riscv_encoding.h b/include/sbi/riscv_encoding.h > index 1d83434..c0e459c 100644 > --- a/include/sbi/riscv_encoding.h > +++ b/include/sbi/riscv_encoding.h > @@ -41,12 +41,14 @@ > #define MSTATUS_GVA _ULL(0x0000004000000000) > #define MSTATUS_GVA_SHIFT 38 > #define MSTATUS_MPV _ULL(0x0000008000000000) > +#define MSTATUS_MDT _ULL(0x0000040000000000) > #else > #define MSTATUSH_SBE _UL(0x00000010) > #define MSTATUSH_MBE _UL(0x00000020) > #define MSTATUSH_GVA _UL(0x00000040) > #define MSTATUSH_GVA_SHIFT 6 > #define MSTATUSH_MPV _UL(0x00000080) > +#define MSTATUSH_MDT _UL(0x00000400) > #endif > #define MSTATUS32_SD _UL(0x80000000) > #define MSTATUS64_SD _ULL(0x8000000000000000)
diff --git a/firmware/fw_base.S b/firmware/fw_base.S index b950c0b..3703cd6 100644 --- a/firmware/fw_base.S +++ b/firmware/fw_base.S @@ -31,6 +31,16 @@ add \__d4, \__s4, zero .endm +.macro CLEAR_MDT tmp +#if __riscv_xlen == 32 + li \tmp, MSTATUSH_MDT + csrc CSR_MSTATUSH, \tmp +#else + li \tmp, MSTATUS_MDT + csrc CSR_MSTATUS, \tmp +#endif +.endm + .section .entry, "ax", %progbits .align 3 .globl _start @@ -91,6 +101,14 @@ _bss_zero: lla s4, _start_hang csrw CSR_MTVEC, s4 + /* + * While at this point, trap handling is rudimentary, if a trap happens, + * it will end up in _start_hang which is enough to hook up a GDB. Clear + * MDT to avoid generating a double trap and thus entering a + * critical-error state. + */ + CLEAR_MDT t0 + /* Setup temporary stack */ lla s4, _fw_end li s5, (SBI_SCRATCH_SIZE * 2) @@ -362,6 +380,9 @@ _start_warm: _skip_trap_handler_hyp: csrw CSR_MTVEC, a4 + /* Clear MDT here again for all harts */ + CLEAR_MDT t0 + /* Initialize SBI runtime */ csrr a0, CSR_MSCRATCH call sbi_init @@ -557,6 +578,9 @@ memcmp: li t0, 0 .endif REG_S t0, (SBI_TRAP_REGS_SIZE + SBI_TRAP_INFO_OFFSET(gva))(sp) + + /* We are ready to take another trap, clear MDT */ + CLEAR_MDT t0 .endm .macro TRAP_CALL_C_ROUTINE @@ -599,15 +623,18 @@ memcmp: .endm .macro TRAP_RESTORE_MEPC_MSTATUS have_mstatush - /* Restore MEPC and MSTATUS CSRs */ - REG_L t0, SBI_TRAP_REGS_OFFSET(mepc)(a0) - csrw CSR_MEPC, t0 + /* + * Restore MSTATUS and MEPC CSRs starting with MSTATUS to set MDT + * flags since we can not take a trap now or MEPC would be cloberred + */ REG_L t0, SBI_TRAP_REGS_OFFSET(mstatus)(a0) csrw CSR_MSTATUS, t0 .if \have_mstatush REG_L t0, SBI_TRAP_REGS_OFFSET(mstatusH)(a0) csrw CSR_MSTATUSH, t0 .endif + REG_L t0, SBI_TRAP_REGS_OFFSET(mepc)(a0) + csrw CSR_MEPC, t0 .endm .macro TRAP_RESTORE_A0_T0 diff --git a/include/sbi/riscv_encoding.h b/include/sbi/riscv_encoding.h index 1d83434..c0e459c 100644 --- a/include/sbi/riscv_encoding.h +++ b/include/sbi/riscv_encoding.h @@ -41,12 +41,14 @@ #define MSTATUS_GVA _ULL(0x0000004000000000) #define MSTATUS_GVA_SHIFT 38 #define MSTATUS_MPV _ULL(0x0000008000000000) +#define MSTATUS_MDT _ULL(0x0000040000000000) #else #define MSTATUSH_SBE _UL(0x00000010) #define MSTATUSH_MBE _UL(0x00000020) #define MSTATUSH_GVA _UL(0x00000040) #define MSTATUSH_GVA_SHIFT 6 #define MSTATUSH_MPV _UL(0x00000080) +#define MSTATUSH_MDT _UL(0x00000400) #endif #define MSTATUS32_SD _UL(0x80000000) #define MSTATUS64_SD _ULL(0x8000000000000000)
Add support for the Smdbltrp[1] ISA extension. First thing to do is clearing MDT on entry after setting the first MTVEC (since MDT is reset to 1). Additionally, during trap handling, clear MDT once all critical CSRs have been saved and in return path, restore MSTATUS before restoring MEPC to avoid taking another trap which would clobber it. Link: https://github.com/riscv/riscv-double-trap/releases/download/v0.56/riscv-double-trap.pdf [1] Signed-off-by: Clément Léger <cleger@rivosinc.com> --- firmware/fw_base.S | 33 ++++++++++++++++++++++++++++++--- include/sbi/riscv_encoding.h | 2 ++ 2 files changed, 32 insertions(+), 3 deletions(-)