Currently riscv gates MMU_GATHER_RCU_TABLE_FREE on CONFIG_SMP and
CONFIG_MMU.
Commit 69be3fb111e7 ("riscv: enable MMU_GATHER_RCU_TABLE_FREE for SMP &&
MMU") enabled CONFIG_MMU_GATHER_RCU_TABLE_FREE for CONFIG_SMP, CONFIG_MMU
riscv builds.
This is expressly for the safety of GUP-fast walkers (CONFIG_HAVE_GUP_FAST
is enabled if CONFIG_MMU is enabled).
Naturally a single core system does not encounter issues with software page
table walkers being correctly synchronised across cores, as there is only a
single core.
However, CONFIG_PREEMPT_RCU is still available on a riscv UP system, so for
a future RCU-only page table walker, this guarantee is required to prevent
concurrent page table teardown.
All page table freeing is already done via tlb_remove_ptdesc() so the
conditions of CONFIG_MMU_GATHER_RCU_TABLE_FREE are already met.
This forms part of an overall effort to switch every architecture to this
mode.
Signed-off-by: Lorenzo Stoakes (ARM) <[email protected]>
---
arch/riscv/Kconfig | 2 +-
1 file changed, 1 insertion(+), 1 deletion(-)
diff --git a/arch/riscv/Kconfig b/arch/riscv/Kconfig
index 505eed4af932..3529ed1861ce 100644
--- a/arch/riscv/Kconfig
+++ b/arch/riscv/Kconfig
@@ -208,7 +208,7 @@ config RISCV
select IRQ_FORCED_THREADING
select KASAN_VMALLOC if KASAN
select LOCK_MM_AND_FIND_VMA
- select MMU_GATHER_RCU_TABLE_FREE if SMP && MMU
+ select MMU_GATHER_RCU_TABLE_FREE if MMU
select MODULES_USE_ELF_RELA if MODULES
select OF
select OF_EARLY_FLATTREE
--
2.55.0
