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linux/arch/riscv
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Naohiko Shimizu e150008568 riscv: suspend: Fix stimecmp update hazard on RV32 
[ Upstream commit 344c5281f4 ]

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: ffef54ad41 ("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>
Signed-off-by: Sasha Levin <sashal@kernel.org>
History 2026-01-30 10:32:16 +01:00
..
boot riscv: boot: Always make Image from vmlinux, not vmlinux.unstripped 2026-01-17 16:35:12 +01:00
configs RISC-V updates for the v6.18 merge window (part two) 2025-10-04 10:36:22 -07:00
crypto lib/crypto: riscv: Depend on RISCV_EFFICIENT_VECTOR_UNALIGNED_ACCESS 2026-01-02 12:57:29 +01:00
errata riscv: errata: Fix the PAUSE Opcode for MIPS P8700 2025-09-19 10:33:56 -06:00
include riscv: pgtable: Cleanup useless VA_USER_XXX definitions 2026-01-17 16:35:25 +01:00
kernel riscv: suspend: Fix stimecmp update hazard on RV32 2026-01-30 10:32:16 +01:00
kvm RISC-V: KVM: Fix guest page fault within HLV* instructions 2025-12-18 14:03:12 +01:00
lib Crypto library updates for 6.17 2025-07-28 17:58:52 -07:00
mm riscv: ptdump: use seq_puts() in pt_dump_seq_puts() macro 2025-10-27 11:40:43 -06:00
net bpf-next-6.18 2025-09-30 17:58:11 -07:00
purgatory kcfi: Rename CONFIG_CFI_CLANG to CONFIG_CFI 2025-09-24 14:29:14 -07:00
tools riscv: Stop considering R_RISCV_NONE as bad relocations 2025-07-16 08:13:55 -07:00
Kbuild riscv: migrate to the generic rule for built-in DTB 2025-03-18 13:30:13 +00:00
Kconfig riscv: Fix CONFIG_AS_HAS_INSN for new .insn usage 2025-11-07 17:39:07 -07:00
Kconfig.debug riscv: Add tests for riscv module loading 2023-11-07 14:59:32 -08:00
Kconfig.errata riscv: errata: Fix the PAUSE Opcode for MIPS P8700 2025-09-19 10:33:56 -06:00
Kconfig.socs riscv: Add Kconfig option for ESWIN platforms 2025-09-25 08:29:05 +02:00
Kconfig.vendor riscv: Add xmipsexectl as a vendor extension 2025-09-18 20:36:00 -06:00
Makefile riscv: Remove redundant judgment for the default build target 2025-11-07 17:39:07 -07:00
Makefile.postlink kbuild: Create intermediate vmlinux build with relocations preserved 2025-03-17 00:29:50 +09:00