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core: riscv: Ensure XSTATUS is restored before XIE
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In previous implementation, we found some accidental interrupts during
entering user mode and resuming of thread. We fixed it by clearing
XSTATUS.XIE first, which is global interrupt enable bit, to ensure there
are no interrupts during those operations.

Now we found the better solution: restore XSTATUS before restoring XIE.
This can ensure the global interrupt bit in XSTATUS is cleared before we
restore the individual interrupt bits in XIE.

Signed-off-by: Alvin Chang <[email protected]>
Reviewed-by: Yu Chien Peter Lin <[email protected]>
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@gagachang @jforissier
gagachang authored and jforissier committed Oct 7, 2024
1 parent 00b4546 commit 9f71579
Showing 1 changed file with 24 additions and 27 deletions.
51 changes: 24 additions & 27 deletions core/arch/riscv/kernel/thread_rv.S
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Original file line number Diff line number Diff line change
Expand Up @@ -148,12 +148,12 @@ native_interrupt_from_kernel:
/* Restore XEPC */
load_xregs sp, THREAD_CTX_REG_EPC, REG_T0
csrw CSR_XEPC, t0
/* Restore XIE */
load_xregs sp, THREAD_CTX_REG_IE, REG_T0
csrw CSR_XIE, t0
/* Restore XSTATUS */
load_xregs sp, THREAD_CTX_REG_STATUS, REG_T0
csrw CSR_XSTATUS, t0
/* Restore XIE */
load_xregs sp, THREAD_CTX_REG_IE, REG_T0
csrw CSR_XIE, t0
/* We are going to XRET to kernel mode. Set XSCRATCH as 0 */
csrw CSR_XSCRATCH, 0
/* Restore all GPRs */
Expand Down Expand Up @@ -246,12 +246,12 @@ set_sp:
/* Restore XEPC */
load_xregs sp, THREAD_ABT_REG_EPC, REG_T0
csrw CSR_XEPC, t0
/* Restore XIE */
load_xregs sp, THREAD_ABT_REG_IE, REG_T0
csrw CSR_XIE, t0
/* Restore XSTATUS */
load_xregs sp, THREAD_ABT_REG_STATUS, REG_T0
csrw CSR_XSTATUS, t0
/* Restore XIE */
load_xregs sp, THREAD_ABT_REG_IE, REG_T0
csrw CSR_XIE, t0
/* We are going to XRET to kernel mode. Set XSCRATCH as 0 */
csrw CSR_XSCRATCH, 0

Expand Down Expand Up @@ -385,12 +385,12 @@ native_interrupt_from_user:
/* Restore XEPC */
load_xregs sp, THREAD_CTX_REG_EPC, REG_T0
csrw CSR_XEPC, t0
/* Restore XIE */
load_xregs sp, THREAD_CTX_REG_IE, REG_T0
csrw CSR_XIE, t0
/* Restore XSTATUS */
load_xregs sp, THREAD_CTX_REG_STATUS, REG_T0
csrw CSR_XSTATUS, t0
/* Restore XIE */
load_xregs sp, THREAD_CTX_REG_IE, REG_T0
csrw CSR_XIE, t0
/* Set scratch as thread_core_local */
csrw CSR_XSCRATCH, tp
/* Restore all GPRs */
Expand Down Expand Up @@ -475,13 +475,14 @@ ecall_from_user:
/* Restore XEPC */
load_xregs sp, THREAD_SCALL_REG_EPC, REG_T0
csrw CSR_XEPC, t0
/* Restore XIE */
load_xregs sp, THREAD_SCALL_REG_IE, REG_T0
csrw CSR_XIE, t0
/* Restore XSTATUS */
load_xregs sp, THREAD_SCALL_REG_STATUS, REG_T0
csrw CSR_XSTATUS, t0
/* Restore XIE */
load_xregs sp, THREAD_SCALL_REG_IE, REG_T0
csrw CSR_XIE, t0
/* Check previous privilege mode by status.SPP */
csrr t0, CSR_XSTATUS
b_if_prev_priv_is_u t0, 1f
/*
* We are going to XRET to kernel mode.
Expand Down Expand Up @@ -588,19 +589,20 @@ abort_from_user:
/* Restore XEPC */
load_xregs sp, THREAD_ABT_REG_EPC, REG_T0
csrw CSR_XEPC, t0
/* Restore XIE */
load_xregs sp, THREAD_ABT_REG_IE, REG_T0
csrw CSR_XIE, t0
/* Restore XSTATUS */
load_xregs sp, THREAD_ABT_REG_STATUS, REG_T0
csrw CSR_XSTATUS, t0
/* Restore XIE */
load_xregs sp, THREAD_ABT_REG_IE, REG_T0
csrw CSR_XIE, t0

/* Update core local flags */
lw a0, THREAD_CORE_LOCAL_FLAGS(tp)
srli a0, a0, THREAD_CLF_SAVED_SHIFT
sw a0, THREAD_CORE_LOCAL_FLAGS(tp)

/* Check previous privilege mode by status.SPP */
csrr t0, CSR_XSTATUS
b_if_prev_priv_is_u t0, 1f
/*
* We are going to XRET to kernel mode.
Expand Down Expand Up @@ -665,9 +667,6 @@ END_FUNC thread_unwind_user_mode
* uint32_t *exit_status1);
*/
FUNC __thread_enter_user_mode , :
/* Disable kernel mode exceptions first */
csrc CSR_XSTATUS, CSR_XSTATUS_IE

/*
* Create and fill in the struct thread_user_mode_rec
*/
Expand Down Expand Up @@ -702,12 +701,12 @@ FUNC __thread_enter_user_mode , :
/* Set exception return PC */
load_xregs sp, THREAD_CTX_REG_EPC, REG_S0
csrw CSR_XEPC, s0
/* Set user ie */
load_xregs sp, THREAD_CTX_REG_IE, REG_S0
csrw CSR_XIE, s0
/* Set user status */
load_xregs sp, THREAD_CTX_REG_STATUS, REG_S0
csrw CSR_XSTATUS, s0
/* Set user ie */
load_xregs sp, THREAD_CTX_REG_IE, REG_S0
csrw CSR_XIE, s0
/* Load the rest of the general purpose registers */
load_xregs sp, THREAD_CTX_REG_RA, REG_RA
load_xregs sp, THREAD_CTX_REG_GP, REG_GP
Expand All @@ -725,23 +724,21 @@ END_FUNC __thread_enter_user_mode

/* void thread_resume(struct thread_ctx_regs *regs) */
FUNC thread_resume , :
/* Disable global interrupts first */
csrc CSR_XSTATUS, CSR_XSTATUS_IE

/* Move struct thread_ctx_regs *regs to sp to reduce code size */
mv sp, a0

/* Restore epc */
load_xregs sp, THREAD_CTX_REG_EPC, REG_T0
csrw CSR_XEPC, t0
/* Restore ie */
load_xregs sp, THREAD_CTX_REG_IE, REG_T0
csrw CSR_XIE, t0
/* Restore status */
load_xregs sp, THREAD_CTX_REG_STATUS, REG_T0
csrw CSR_XSTATUS, t0
/* Restore ie */
load_xregs sp, THREAD_CTX_REG_IE, REG_T0
csrw CSR_XIE, t0

/* Check if previous privilege mode by status.SPP */
csrr t0, CSR_XSTATUS
b_if_prev_priv_is_u t0, 1f
/* Set scratch as zero to indicate that we are in kernel mode */
csrw CSR_XSCRATCH, zero
Expand Down

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