diff options
| author | Naohiko Shimizu <naohiko.shimizu@gmail.com> | 2026-01-04 22:59:38 +0900 |
|---|---|---|
| committer | Paul Walmsley <pjw@kernel.org> | 2026-01-14 17:43:22 -0700 |
| commit | 344c5281f43851b22c7cc223fd0250c143fcbc79 (patch) | |
| tree | d64935268f9e4345cec143c726ee55f1b174fe7e | |
| parent | 75870639bf5d1c447ddba4d738ff72771a69f2a1 (diff) | |
riscv: suspend: Fix stimecmp update hazard on RV32
On RV32, updating the 64-bit stimecmp (or vstimecmp) CSR requires two
separate 32-bit writes. A race condition exists if the timer triggers
during these two writes.
The RISC-V Privileged Specification (e.g., Section 3.2.1 for mtimecmp)
recommends a specific 3-step sequence to avoid spurious interrupts
when updating 64-bit comparison registers on 32-bit systems:
1. Set the low-order bits (stimecmp) to all ones (ULONG_MAX).
2. Set the high-order bits (stimecmph) to the desired value.
3. Set the low-order bits (stimecmp) to the desired value.
Current implementation writes the LSB first without ensuring a future
value, which may lead to a transient state where the 64-bit comparison
is incorrectly evaluated as "expired" by the hardware. This results in
spurious timer interrupts.
This patch adopts the spec-recommended 3-step sequence to ensure the
intermediate 64-bit state is never smaller than the current time.
Fixes: ffef54ad4110 ("riscv: Add stimecmp save and restore")
Signed-off-by: Naohiko Shimizu <naohiko.shimizu@gmail.com>
Reviewed-by: Anup Patel <anup@brainfault.org>
Link: https://patch.msgid.link/20260104135938.524-4-naohiko.shimizu@gmail.com
Signed-off-by: Paul Walmsley <pjw@kernel.org>
| -rw-r--r-- | arch/riscv/kernel/suspend.c | 3 |
1 files changed, 2 insertions, 1 deletions
diff --git a/arch/riscv/kernel/suspend.c b/arch/riscv/kernel/suspend.c index 24b3f57d467f..aff93090c4ef 100644 --- a/arch/riscv/kernel/suspend.c +++ b/arch/riscv/kernel/suspend.c @@ -51,10 +51,11 @@ void suspend_restore_csrs(struct suspend_context *context) #ifdef CONFIG_MMU if (riscv_has_extension_unlikely(RISCV_ISA_EXT_SSTC)) { - csr_write(CSR_STIMECMP, context->stimecmp); #if __riscv_xlen < 64 + csr_write(CSR_STIMECMP, ULONG_MAX); csr_write(CSR_STIMECMPH, context->stimecmph); #endif + csr_write(CSR_STIMECMP, context->stimecmp); } csr_write(CSR_SATP, context->satp); |