[RFC PATCH v12 14/26] mm/rmap: recognize read-only tlb entries during batched tlb flush

Byungchul Park
2025-02-20T05:36:04Z

Functionally, no change. This is a preparation for luf mechanism that
requires to recognize read-only tlb entries and handle them in a
different way. The newly introduced API in this patch, fold_ubc(), will
be used by luf mechanism.

Signed-off-by: Byungchul Park <byungchul@sk.com>
---
include/linux/sched.h | 1 +
mm/rmap.c | 16 ++++++++++++++--
2 files changed, 15 insertions(+), 2 deletions(-)

diff --git a/include/linux/sched.h b/include/linux/sched.h
index c4ff83e1d5953..a217d6011fdfe 100644
--- a/include/linux/sched.h
+++ b/include/linux/sched.h
@@ -1381,6 +1381,7 @@ struct task_struct {

struct tlbflush_unmap_batch tlb_ubc;
struct tlbflush_unmap_batch tlb_ubc_takeoff;
+ struct tlbflush_unmap_batch tlb_ubc_ro;

/* Cache last used pipe for splice(): */
struct pipe_inode_info *splice_pipe;
diff --git a/mm/rmap.c b/mm/rmap.c
index 1581b1a00f974..3ed6234dd777e 100644
--- a/mm/rmap.c
+++ b/mm/rmap.c
@@ -775,6 +775,7 @@ void fold_luf_batch(struct luf_batch *dst, struct luf_batch *src)
void try_to_unmap_flush_takeoff(void)
{
struct tlbflush_unmap_batch *tlb_ubc = &current->tlb_ubc;
+ struct tlbflush_unmap_batch *tlb_ubc_ro = &current->tlb_ubc_ro;
struct tlbflush_unmap_batch *tlb_ubc_takeoff = &current->tlb_ubc_takeoff;

if (!tlb_ubc_takeoff->flush_required)
@@ -789,6 +790,9 @@ void try_to_unmap_flush_takeoff(void)
if (arch_tlbbatch_done(&tlb_ubc->arch, &tlb_ubc_takeoff->arch))
reset_batch(tlb_ubc);

+ if (arch_tlbbatch_done(&tlb_ubc_ro->arch, &tlb_ubc_takeoff->arch))
+ reset_batch(tlb_ubc_ro);
+
reset_batch(tlb_ubc_takeoff);
}

@@ -801,7 +805,9 @@ void try_to_unmap_flush_takeoff(void)
void try_to_unmap_flush(void)
{
struct tlbflush_unmap_batch *tlb_ubc = &current->tlb_ubc;
+ struct tlbflush_unmap_batch *tlb_ubc_ro = &current->tlb_ubc_ro;

+ fold_batch(tlb_ubc, tlb_ubc_ro, true);
if (!tlb_ubc->flush_required)
return;

@@ -813,8 +819,9 @@ void try_to_unmap_flush(void)
void try_to_unmap_flush_dirty(void)
{
struct tlbflush_unmap_batch *tlb_ubc = &current->tlb_ubc;
+ struct tlbflush_unmap_batch *tlb_ubc_ro = &current->tlb_ubc_ro;

- if (tlb_ubc->writable)
+ if (tlb_ubc->writable || tlb_ubc_ro->writable)
try_to_unmap_flush();
}

@@ -831,13 +838,18 @@ void try_to_unmap_flush_dirty(void)
static void set_tlb_ubc_flush_pending(struct mm_struct *mm, pte_t pteval,
unsigned long uaddr)
{
- struct tlbflush_unmap_batch *tlb_ubc = &current->tlb_ubc;
+ struct tlbflush_unmap_batch *tlb_ubc;
int batch;
bool writable = pte_dirty(pteval);

if (!pte_accessible(mm, pteval))
return;

+ if (pte_write(pteval))
+ tlb_ubc = &current->tlb_ubc;
+ else
+ tlb_ubc = &current->tlb_ubc_ro;
+
arch_tlbbatch_add_pending(&tlb_ubc->arch, mm, uaddr);
tlb_ubc->flush_required = true;

--
2.17.1