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Message-ID: <20250809135137.259427-2-thomas.hellstrom@linux.intel.com>
Date: Sat, 9 Aug 2025 15:51:32 +0200
From: Thomas Hellström <thomas.hellstrom@...ux.intel.com>
To: intel-xe@...ts.freedesktop.org
Cc: Thomas Hellström <thomas.hellstrom@...ux.intel.com>,
Jason Gunthorpe <jgg@...pe.ca>,
Andrew Morton <akpm@...ux-foundation.org>,
Simona Vetter <simona.vetter@...ll.ch>,
Dave Airlie <airlied@...il.com>,
dri-devel@...ts.freedesktop.org,
linux-mm@...ck.org,
linux-kernel@...r.kernel.org,
Matthew Brost <matthew.brost@...el.com>,
Christian König <christian.koenig@....com>
Subject: [RFC PATCH 1/6] mm/mmu_notifier: Allow multiple struct mmu_interval_notifier passes
GPU use-cases for mmu_interval_notifiers with hmm often involve
starting a gpu operation and then waiting for it to complete.
These operations are typically context preemption or TLB flushing.
With single-pass notifiers per GPU this doesn't scale in
multi-gpu scenarios. In those scenarios we'd want to first start
preemption- or TLB flushing on all GPUs and as a second pass wait
for them to complete on all gpus.
One can do this on per-driver basis multiplexing per-driver
notifiers but that would mean sharing the notifier "user" lock
across all GPUs and that doesn't scale well either, so adding support
for multi-pass in the core appears like the right choice.
Implement multi-pass capability in the mmu_interval_notifier. Use a
linked list for the additional passes to minimize the impact for
use-cases that don't need the multi-pass functionality.
Cc: Jason Gunthorpe <jgg@...pe.ca>
Cc: Andrew Morton <akpm@...ux-foundation.org>
Cc: Simona Vetter <simona.vetter@...ll.ch>
Cc: Dave Airlie <airlied@...il.com>
Cc: <dri-devel@...ts.freedesktop.org>
Cc: <linux-mm@...ck.org>
Cc: <linux-kernel@...r.kernel.org>
Signed-off-by: Thomas Hellström <thomas.hellstrom@...ux.intel.com>
---
include/linux/mmu_notifier.h | 30 ++++++++++++++++
mm/mmu_notifier.c | 67 +++++++++++++++++++++++++++++++-----
2 files changed, 88 insertions(+), 9 deletions(-)
diff --git a/include/linux/mmu_notifier.h b/include/linux/mmu_notifier.h
index d1094c2d5fb6..1107a8eafd8a 100644
--- a/include/linux/mmu_notifier.h
+++ b/include/linux/mmu_notifier.h
@@ -233,6 +233,32 @@ struct mmu_notifier {
unsigned int users;
};
+/**
+ * struct mmu_interval_notifier_pass - mmu_interval_notifier multi-pass abstraction
+ * @link: List link for the notifiers pending pass list
+ *
+ * Allocate, typically using GFP_NOWAIT in the interval notifier's first pass.
+ * If allocation fails (which is not unlikely under memory pressure), fall back
+ * to single-pass operation.
+ */
+struct mmu_interval_notifier_pass {
+ struct list_head link;
+ /**
+ * @pass: Driver callback for additionall pass.
+ * @additional_pass: Pointer to the mmu_interval_notifier_pass structure.
+ * @range: The mmu_notifier_range.
+ * @cur_seq: The current sequence set by the first pass.
+ *
+ * Return: Either a pointer to a valid mmu_interval_notifier_pass for
+ * another pass to be called, or %NULL if processing is complete for this
+ * notifier. There is no error reporting mechanism for additional passes.
+ */
+ struct mmu_interval_notifier_pass *
+ (*pass) (struct mmu_interval_notifier_pass *additional_pass,
+ const struct mmu_notifier_range *range,
+ unsigned long cur_seq);
+};
+
/**
* struct mmu_interval_notifier_ops
* @invalidate: Upon return the caller must stop using any SPTEs within this
@@ -243,6 +269,10 @@ struct mmu_interval_notifier_ops {
bool (*invalidate)(struct mmu_interval_notifier *interval_sub,
const struct mmu_notifier_range *range,
unsigned long cur_seq);
+ bool (*invalidate_multipass)(struct mmu_interval_notifier *interval_sub,
+ const struct mmu_notifier_range *range,
+ unsigned long cur_seq,
+ struct mmu_interval_notifier_pass **pass);
};
struct mmu_interval_notifier {
diff --git a/mm/mmu_notifier.c b/mm/mmu_notifier.c
index 8e0125dc0522..dd6af87db103 100644
--- a/mm/mmu_notifier.c
+++ b/mm/mmu_notifier.c
@@ -260,6 +260,22 @@ mmu_interval_read_begin(struct mmu_interval_notifier *interval_sub)
}
EXPORT_SYMBOL_GPL(mmu_interval_read_begin);
+static void mn_itree_additional_passes(struct list_head *additional_passes,
+ const struct mmu_notifier_range *range,
+ unsigned long cur_seq)
+{
+ struct mmu_interval_notifier_pass *p, *next;
+
+ while (!list_empty(additional_passes)) {
+ list_for_each_entry_safe(p, next, additional_passes, link) {
+ list_del_init(&p->link);
+ p = p->pass(p, range, cur_seq);
+ if (p)
+ list_add_tail(&p->link, additional_passes);
+ }
+ }
+}
+
static void mn_itree_release(struct mmu_notifier_subscriptions *subscriptions,
struct mm_struct *mm)
{
@@ -272,17 +288,32 @@ static void mn_itree_release(struct mmu_notifier_subscriptions *subscriptions,
};
struct mmu_interval_notifier *interval_sub;
unsigned long cur_seq;
+ LIST_HEAD(additional_passes);
bool ret;
for (interval_sub =
mn_itree_inv_start_range(subscriptions, &range, &cur_seq);
interval_sub;
interval_sub = mn_itree_inv_next(interval_sub, &range)) {
- ret = interval_sub->ops->invalidate(interval_sub, &range,
- cur_seq);
+ if (interval_sub->ops->invalidate_multipass) {
+ struct mmu_interval_notifier_pass *second = NULL;
+
+ ret = interval_sub->ops->invalidate_multipass(interval_sub,
+ &range,
+ cur_seq,
+ &second);
+ if (ret && second)
+ list_add_tail(&second->link, &additional_passes);
+
+ } else {
+ ret = interval_sub->ops->invalidate(interval_sub,
+ &range,
+ cur_seq);
+ }
WARN_ON(!ret);
}
+ mn_itree_additional_passes(&additional_passes, &range, cur_seq);
mn_itree_inv_end(subscriptions);
}
@@ -431,6 +462,8 @@ static int mn_itree_invalidate(struct mmu_notifier_subscriptions *subscriptions,
{
struct mmu_interval_notifier *interval_sub;
unsigned long cur_seq;
+ LIST_HEAD(additional_passes);
+ int err = 0;
for (interval_sub =
mn_itree_inv_start_range(subscriptions, range, &cur_seq);
@@ -438,23 +471,39 @@ static int mn_itree_invalidate(struct mmu_notifier_subscriptions *subscriptions,
interval_sub = mn_itree_inv_next(interval_sub, range)) {
bool ret;
- ret = interval_sub->ops->invalidate(interval_sub, range,
- cur_seq);
+ if (interval_sub->ops->invalidate_multipass) {
+ struct mmu_interval_notifier_pass *second = NULL;
+
+ ret = interval_sub->ops->invalidate_multipass(interval_sub,
+ range,
+ cur_seq,
+ &second);
+ if (ret && second)
+ list_add_tail(&second->link, &additional_passes);
+
+ } else {
+ ret = interval_sub->ops->invalidate(interval_sub,
+ range,
+ cur_seq);
+ }
if (!ret) {
if (WARN_ON(mmu_notifier_range_blockable(range)))
continue;
- goto out_would_block;
+ err = -EAGAIN;
+ break;
}
}
- return 0;
-out_would_block:
+ mn_itree_additional_passes(&additional_passes, range, cur_seq);
+
/*
* On -EAGAIN the non-blocking caller is not allowed to call
* invalidate_range_end()
*/
- mn_itree_inv_end(subscriptions);
- return -EAGAIN;
+ if (err)
+ mn_itree_inv_end(subscriptions);
+
+ return err;
}
static int mn_hlist_invalidate_range_start(
--
2.50.1
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