*/
.macro RESTORE_ALL
REG_L a0, PT_SSTATUS(sp)
- REG_L a2, PT_SEPC(sp)
+ /*
+ * The current load reservation is effectively part of the processor's
+ * state, in the sense that load reservations cannot be shared between
+ * different hart contexts. We can't actually save and restore a load
+ * reservation, so instead here we clear any existing reservation --
+ * it's always legal for implementations to clear load reservations at
+ * any point (as long as the forward progress guarantee is kept, but
+ * we'll ignore that here).
+ *
+ * Dangling load reservations can be the result of taking a trap in the
+ * middle of an LR/SC sequence, but can also be the result of a taken
+ * forward branch around an SC -- which is how we implement CAS. As a
+ * result we need to clear reservations between the last CAS and the
+ * jump back to the new context. While it is unlikely the store
+ * completes, implementations are allowed to expand reservations to be
+ * arbitrarily large.
+ */
+ REG_L a2, PT_SEPC(sp)
+ REG_SC x0, a2, PT_SEPC(sp)
+
csrw CSR_SSTATUS, a0
csrw CSR_SEPC, a2
move a0, sp /* pt_regs */
tail do_IRQ
1:
- /* Exceptions run with interrupts enabled */
+ /* Exceptions run with interrupts enabled or disabled
+ depending on the state of sstatus.SR_SPIE */
+ andi t0, s1, SR_SPIE
+ beqz t0, 1f
csrs CSR_SSTATUS, SR_SIE
+1:
/* Handle syscalls */
li t0, EXC_SYSCALL
beq s4, t0, handle_syscall