Commit a0ad5496b2b3 ("arm: mm: enable HAVE_RCU_TABLE_FREE logic") enabled
CONFIG_MMU_GATHER_RCU_TABLE_FREE (then named HAVE_RCU_TABLE_FREE) for SMP
arm architectures with LPAE enabled.
Regardless of whether CONFIG_ARM_LPAE is enabled or not, the same page
table freeing functions __pte_free_tlb() and __pmd_free_tlb() are used.
Non-LPAE PMD page tables are folded into the PGD and freed by
pgd_free() (PGD freeing is not part of mmu_gather page table freeing in any
case), so this is a noop in this case.
Since commit 358d1c39c82a ("arm: convert various functions to use ptdescs")
both LPAE and non-LPAE PTE page table freeing uses tlb_remove_ptdesc().
Thus all page table freeing is performed under RCU with
CONFIG_MMU_GATHER_RCU_TABLE_FREE enabled for LPAE and non-LPAE and thus it
need not be gated on LPAE.
A UP arm system can set CONFIG_PREEMPT_RCU, so a future pure RCU page
table walker requires MMU_GATHER_RCU_TABLE_FREE to be enabled on UP as
well, even if concurrent GUP fast is not possible there.
Therefore, it is both safe and desirable to set
CONFIG_MMU_GATHER_RCU_TABLE_FREE for all MMU arm architectures (nommu does
not perform mmu_gather operations).
This forms part of an overall effort to switch every architecture to this
mode.
Signed-off-by: Lorenzo Stoakes (ARM) <[email protected]>
---
arch/arm/Kconfig | 2 +-
1 file changed, 1 insertion(+), 1 deletion(-)
diff --git a/arch/arm/Kconfig b/arch/arm/Kconfig
index 408aa58a2a5b..72b9afc6ae10 100644
--- a/arch/arm/Kconfig
+++ b/arch/arm/Kconfig
@@ -134,7 +134,7 @@ config ARM
select HAVE_PERF_REGS
select HAVE_PERF_USER_STACK_DUMP
select HAVE_POSIX_CPU_TIMERS_TASK_WORK
- select MMU_GATHER_RCU_TABLE_FREE if SMP && ARM_LPAE
+ select MMU_GATHER_RCU_TABLE_FREE if MMU
select HAVE_REGS_AND_STACK_ACCESS_API
select HAVE_RSEQ
select HAVE_RUST if CPU_LITTLE_ENDIAN && CPU_32v7 && !KASAN
--
2.55.0
