[RFC PATCH v12 based on v6.14-rc4 03/25] riscv/tlb: add APIs manipulating tlb batch's arch data

Byungchul Park
2025-02-26T12:03:47Z

A new mechanism, LUF(Lazy Unmap Flush), defers tlb flush until folios
that have been unmapped and freed, eventually get allocated again. It's
safe for folios that had been mapped read only and were unmapped, since
the contents of the folios don't change while staying in pcp or buddy
so we can still read the data through the stale tlb entries.

This is a preparation for the mechanism that needs to recognize
read-only tlb entries by separating tlb batch arch data into two, one is
for read-only entries and the other is for writable ones, and merging
those two when needed.

It also optimizes tlb shootdown by skipping CPUs that have already
performed tlb flush needed since. To support it, added APIs
manipulating arch data for riscv.

Signed-off-by: Byungchul Park <byungchul@sk.com>
---
arch/riscv/include/asm/tlbflush.h | 28 ++++++++++++++++++++++++++++
1 file changed, 28 insertions(+)

diff --git a/arch/riscv/include/asm/tlbflush.h b/arch/riscv/include/asm/tlbflush.h
index 72e5599349529..1dc7d30273d59 100644
--- a/arch/riscv/include/asm/tlbflush.h
+++ b/arch/riscv/include/asm/tlbflush.h
@@ -8,6 +8,7 @@
#define _ASM_RISCV_TLBFLUSH_H

#include <linux/mm_types.h>
+#include <linux/cpumask.h>
#include <asm/smp.h>
#include <asm/errata_list.h>

@@ -65,6 +66,33 @@ void arch_tlbbatch_add_pending(struct arch_tlbflush_unmap_batch *batch,
void arch_flush_tlb_batched_pending(struct mm_struct *mm);
void arch_tlbbatch_flush(struct arch_tlbflush_unmap_batch *batch);

+static inline void arch_tlbbatch_clear(struct arch_tlbflush_unmap_batch *batch)
+{
+ cpumask_clear(&batch->cpumask);
+
+}
+
+static inline void arch_tlbbatch_fold(struct arch_tlbflush_unmap_batch *bdst,
+ struct arch_tlbflush_unmap_batch *bsrc)
+{
+ cpumask_or(&bdst->cpumask, &bdst->cpumask, &bsrc->cpumask);
+
+}
+
+static inline bool arch_tlbbatch_need_fold(struct arch_tlbflush_unmap_batch *batch,
+ struct mm_struct *mm)
+{
+ return !cpumask_subset(mm_cpumask(mm), &batch->cpumask);
+
+}
+
+static inline bool arch_tlbbatch_done(struct arch_tlbflush_unmap_batch *bdst,
+ struct arch_tlbflush_unmap_batch *bsrc)
+{
+ return !cpumask_andnot(&bdst->cpumask, &bdst->cpumask, &bsrc->cpumask);
+
+}
+
extern unsigned long tlb_flush_all_threshold;
#else /* CONFIG_MMU */
#define local_flush_tlb_all() do { } while (0)
--
2.17.1