diff mbox series

[v10,5/6] iommu/dma: Allow a single FQ in addition to per-CPU FQs

Message ID 20230310-dma_iommu-v10-5-f1fbd8310854@linux.ibm.com (mailing list archive)
State Superseded
Headers show
Series iommu/dma: s390 DMA API conversion and optimized IOTLB flushing | expand

Commit Message

Niklas Schnelle May 24, 2023, 2:53 p.m. UTC 
In some virtualized environments, including s390 paged memory guests,
IOTLB flushes are used to update IOMMU shadow tables. Due to this, they
are much more expensive than in typical bare metal environments or
non-paged s390 guests. In addition they may parallelize poorly in
virtualized environments. This changes the trade off for flushing IOVAs
such that minimizing the number of IOTLB flushes trumps any benefit of
cheaper queuing operations or increased paralellism.

In this scenario per-CPU flush queues pose several problems. Firstly
per-CPU memory is often quite limited prohibiting larger queues.
Secondly collecting IOVAs per-CPU but flushing via a global timeout
reduces the number of IOVAs flushed for each timeout especially on s390
where PCI interrupts may not be bound to a specific CPU.

Let's introduce a single flush queue mode that reuses the same queue
logic but only allocates a single global queue. This mode is selected by
dma-iommu if a newly introduced .shadow_on_flush flag is set in struct
dev_iommu. As a first user the s390 IOMMU driver sets this flag during
probe_device. With the unchanged small FQ size and timeouts this setting
is worse than per-CPU queues but a follow up patch will make the FQ size
and timeout variable. Together this allows the common IOVA flushing code
to more closely resemble the global flush behavior used on s390's
previous internal DMA API implementation.

Link: https://lore.kernel.org/linux-iommu/3e402947-61f9-b7e8-1414-fde006257b6f@arm.com/
Reviewed-by: Matthew Rosato <mjrosato@linux.ibm.com> #s390
Signed-off-by: Niklas Schnelle <schnelle@linux.ibm.com>
---
 drivers/iommu/dma-iommu.c  | 177 ++++++++++++++++++++++++++++++++++-----------
 drivers/iommu/iommu.c      |  20 +----
 drivers/iommu/s390-iommu.c |   3 +
 include/linux/iommu.h      |   2 +
 4 files changed, 142 insertions(+), 60 deletions(-)

Comments

Niklas Schnelle June 22, 2023, 12:47 p.m. UTC | #1 
On Wed, 2023-05-24 at 16:53 +0200, Niklas Schnelle wrote:
> In some virtualized environments, including s390 paged memory guests,
> IOTLB flushes are used to update IOMMU shadow tables. Due to this, they
> are much more expensive than in typical bare metal environments or
> non-paged s390 guests. In addition they may parallelize poorly in
> virtualized environments. This changes the trade off for flushing IOVAs
> such that minimizing the number of IOTLB flushes trumps any benefit of
> cheaper queuing operations or increased paralellism.
> 
> In this scenario per-CPU flush queues pose several problems. Firstly
> per-CPU memory is often quite limited prohibiting larger queues.
> Secondly collecting IOVAs per-CPU but flushing via a global timeout
> reduces the number of IOVAs flushed for each timeout especially on s390
> where PCI interrupts may not be bound to a specific CPU.
> 
> Let's introduce a single flush queue mode that reuses the same queue
> logic but only allocates a single global queue. This mode is selected by
> dma-iommu if a newly introduced .shadow_on_flush flag is set in struct
> dev_iommu. As a first user the s390 IOMMU driver sets this flag during
> probe_device. With the unchanged small FQ size and timeouts this setting
> is worse than per-CPU queues but a follow up patch will make the FQ size
> and timeout variable. Together this allows the common IOVA flushing code
> to more closely resemble the global flush behavior used on s390's
> previous internal DMA API implementation.
> 
> Link: https://lore.kernel.org/linux-iommu/3e402947-61f9-b7e8-1414-fde006257b6f@arm.com/
> Reviewed-by: Matthew Rosato <mjrosato@linux.ibm.com> #s390
> Signed-off-by: Niklas Schnelle <schnelle@linux.ibm.com>
> ---

Gentle ping. As stated in the cover letter this version aimed to
resolve the only outstanding feedback of removing the .tune_dma_iommu()
op in favor of a .shadow_on_flush flag in struct dev_iommu. This then
let's the dma-iommu choose a single queue and larger timeouts and IOVA
counts. This leaves the dma-iommu  with full responsibility for the
settings.

Thanks,
Niklas
diff mbox series

Patch

diff --git a/drivers/iommu/dma-iommu.c b/drivers/iommu/dma-iommu.c
index 7a9f0b0bddbd..85f629769b42 100644
--- a/drivers/iommu/dma-iommu.c
+++ b/drivers/iommu/dma-iommu.c
@@ -43,14 +43,23 @@  enum iommu_dma_cookie_type {
 	IOMMU_DMA_MSI_COOKIE,
 };
 
+struct dma_iommu_options {
+#define IOMMU_DMA_OPTS_PER_CPU_QUEUE	0L
+#define IOMMU_DMA_OPTS_SINGLE_QUEUE	BIT(0)
+	u64	flags;
+};
+
 struct iommu_dma_cookie {
 	enum iommu_dma_cookie_type	type;
 	union {
 		/* Full allocator for IOMMU_DMA_IOVA_COOKIE */
 		struct {
 			struct iova_domain	iovad;
-
-			struct iova_fq __percpu *fq;	/* Flush queue */
+			/* Flush queue */
+			union {
+				struct iova_fq	*single_fq;
+				struct iova_fq	__percpu *percpu_fq;
+			};
 			/* Number of TLB flushes that have been started */
 			atomic64_t		fq_flush_start_cnt;
 			/* Number of TLB flushes that have been finished */
@@ -67,6 +76,8 @@  struct iommu_dma_cookie {
 
 	/* Domain for flush queue callback; NULL if flush queue not in use */
 	struct iommu_domain		*fq_domain;
+	/* Options for dma-iommu use */
+	struct dma_iommu_options	options;
 	struct mutex			mutex;
 };
 
@@ -124,7 +135,7 @@  static inline unsigned int fq_ring_add(struct iova_fq *fq)
 	return idx;
 }
 
-static void fq_ring_free(struct iommu_dma_cookie *cookie, struct iova_fq *fq)
+static void fq_ring_free_locked(struct iommu_dma_cookie *cookie, struct iova_fq *fq)
 {
 	u64 counter = atomic64_read(&cookie->fq_flush_finish_cnt);
 	unsigned int idx;
@@ -145,6 +156,15 @@  static void fq_ring_free(struct iommu_dma_cookie *cookie, struct iova_fq *fq)
 	}
 }
 
+static void fq_ring_free(struct iommu_dma_cookie *cookie, struct iova_fq *fq)
+{
+	unsigned long flags;
+
+	spin_lock_irqsave(&fq->lock, flags);
+	fq_ring_free_locked(cookie, fq);
+	spin_unlock_irqrestore(&fq->lock, flags);
+}
+
 static void fq_flush_iotlb(struct iommu_dma_cookie *cookie)
 {
 	atomic64_inc(&cookie->fq_flush_start_cnt);
@@ -152,23 +172,29 @@  static void fq_flush_iotlb(struct iommu_dma_cookie *cookie)
 	atomic64_inc(&cookie->fq_flush_finish_cnt);
 }
 
+static void fq_flush_percpu(struct iommu_dma_cookie *cookie)
+{
+	int cpu;
+
+	for_each_possible_cpu(cpu) {
+		struct iova_fq *fq;
+
+		fq = per_cpu_ptr(cookie->percpu_fq, cpu);
+		fq_ring_free(cookie, fq);
+	}
+}
+
 static void fq_flush_timeout(struct timer_list *t)
 {
 	struct iommu_dma_cookie *cookie = from_timer(cookie, t, fq_timer);
-	int cpu;
 
 	atomic_set(&cookie->fq_timer_on, 0);
 	fq_flush_iotlb(cookie);
 
-	for_each_possible_cpu(cpu) {
-		unsigned long flags;
-		struct iova_fq *fq;
-
-		fq = per_cpu_ptr(cookie->fq, cpu);
-		spin_lock_irqsave(&fq->lock, flags);
-		fq_ring_free(cookie, fq);
-		spin_unlock_irqrestore(&fq->lock, flags);
-	}
+	if (cookie->options.flags & IOMMU_DMA_OPTS_SINGLE_QUEUE)
+		fq_ring_free(cookie, cookie->single_fq);
+	else
+		fq_flush_percpu(cookie);
 }
 
 static void queue_iova(struct iommu_dma_cookie *cookie,
@@ -188,7 +214,11 @@  static void queue_iova(struct iommu_dma_cookie *cookie,
 	 */
 	smp_mb();
 
-	fq = raw_cpu_ptr(cookie->fq);
+	if (cookie->options.flags & IOMMU_DMA_OPTS_SINGLE_QUEUE)
+		fq = cookie->single_fq;
+	else
+		fq = raw_cpu_ptr(cookie->percpu_fq);
+
 	spin_lock_irqsave(&fq->lock, flags);
 
 	/*
@@ -196,11 +226,11 @@  static void queue_iova(struct iommu_dma_cookie *cookie,
 	 * flushed out on another CPU. This makes the fq_full() check below less
 	 * likely to be true.
 	 */
-	fq_ring_free(cookie, fq);
+	fq_ring_free_locked(cookie, fq);
 
 	if (fq_full(fq)) {
 		fq_flush_iotlb(cookie);
-		fq_ring_free(cookie, fq);
+		fq_ring_free_locked(cookie, fq);
 	}
 
 	idx = fq_ring_add(fq);
@@ -219,31 +249,90 @@  static void queue_iova(struct iommu_dma_cookie *cookie,
 			  jiffies + msecs_to_jiffies(IOVA_FQ_TIMEOUT));
 }
 
-static void iommu_dma_free_fq(struct iommu_dma_cookie *cookie)
+static void iommu_dma_free_fq_single(struct iova_fq *fq)
+{
+	int idx;
+
+	if (!fq)
+		return;
+	fq_ring_for_each(idx, fq)
+		put_pages_list(&fq->entries[idx].freelist);
+	vfree(fq);
+}
+
+static void iommu_dma_free_fq_percpu(struct iova_fq __percpu *percpu_fq)
 {
 	int cpu, idx;
 
-	if (!cookie->fq)
-		return;
-
-	del_timer_sync(&cookie->fq_timer);
 	/* The IOVAs will be torn down separately, so just free our queued pages */
 	for_each_possible_cpu(cpu) {
-		struct iova_fq *fq = per_cpu_ptr(cookie->fq, cpu);
+		struct iova_fq *fq = per_cpu_ptr(percpu_fq, cpu);
 
 		fq_ring_for_each(idx, fq)
 			put_pages_list(&fq->entries[idx].freelist);
 	}
 
-	free_percpu(cookie->fq);
+	free_percpu(percpu_fq);
+}
+
+static void iommu_dma_free_fq(struct iommu_dma_cookie *cookie)
+{
+	if (!cookie->fq_domain)
+		return;
+
+	del_timer_sync(&cookie->fq_timer);
+	if (cookie->options.flags & IOMMU_DMA_OPTS_SINGLE_QUEUE)
+		iommu_dma_free_fq_single(cookie->single_fq);
+	else
+		iommu_dma_free_fq_percpu(cookie->percpu_fq);
+}
+
+static void iommu_dma_init_one_fq(struct iova_fq *fq)
+{
+	int i;
+
+	fq->head = 0;
+	fq->tail = 0;
+
+	spin_lock_init(&fq->lock);
+
+	for (i = 0; i < IOVA_FQ_SIZE; i++)
+		INIT_LIST_HEAD(&fq->entries[i].freelist);
+}
+
+static int iommu_dma_init_fq_single(struct iommu_dma_cookie *cookie)
+{
+	struct iova_fq *queue;
+
+	queue = vzalloc(sizeof(*queue));
+	if (!queue)
+		return -ENOMEM;
+	iommu_dma_init_one_fq(queue);
+	cookie->single_fq = queue;
+
+	return 0;
+}
+
+static int iommu_dma_init_fq_percpu(struct iommu_dma_cookie *cookie)
+{
+	struct iova_fq __percpu *queue;
+	int cpu;
+
+	queue = alloc_percpu(struct iova_fq);
+	if (!queue)
+		return -ENOMEM;
+
+	for_each_possible_cpu(cpu)
+		iommu_dma_init_one_fq(per_cpu_ptr(queue, cpu));
+	cookie->percpu_fq = queue;
+	return 0;
 }
 
 /* sysfs updates are serialised by the mutex of the group owning @domain */
 int iommu_dma_init_fq(struct iommu_domain *domain)
 {
 	struct iommu_dma_cookie *cookie = domain->iova_cookie;
-	struct iova_fq __percpu *queue;
-	int i, cpu;
+	int rc;
 
 	if (cookie->fq_domain)
 		return 0;
@@ -251,26 +340,16 @@  int iommu_dma_init_fq(struct iommu_domain *domain)
 	atomic64_set(&cookie->fq_flush_start_cnt,  0);
 	atomic64_set(&cookie->fq_flush_finish_cnt, 0);
 
-	queue = alloc_percpu(struct iova_fq);
-	if (!queue) {
+	if (cookie->options.flags & IOMMU_DMA_OPTS_SINGLE_QUEUE)
+		rc = iommu_dma_init_fq_single(cookie);
+	else
+		rc = iommu_dma_init_fq_percpu(cookie);
+
+	if (rc) {
 		pr_warn("iova flush queue initialization failed\n");
 		return -ENOMEM;
 	}
 
-	for_each_possible_cpu(cpu) {
-		struct iova_fq *fq = per_cpu_ptr(queue, cpu);
-
-		fq->head = 0;
-		fq->tail = 0;
-
-		spin_lock_init(&fq->lock);
-
-		for (i = 0; i < IOVA_FQ_SIZE; i++)
-			INIT_LIST_HEAD(&fq->entries[i].freelist);
-	}
-
-	cookie->fq = queue;
-
 	timer_setup(&cookie->fq_timer, fq_flush_timeout, 0);
 	atomic_set(&cookie->fq_timer_on, 0);
 	/*
@@ -297,6 +376,7 @@  static struct iommu_dma_cookie *cookie_alloc(enum iommu_dma_cookie_type type)
 	if (cookie) {
 		INIT_LIST_HEAD(&cookie->msi_page_list);
 		cookie->type = type;
+		cookie->options.flags = IOMMU_DMA_OPTS_PER_CPU_QUEUE;
 	}
 	return cookie;
 }
@@ -585,9 +665,18 @@  static int iommu_dma_init_domain(struct iommu_domain *domain, dma_addr_t base,
 	if (ret)
 		goto done_unlock;
 
-	/* If the FQ fails we can simply fall back to strict mode */
-	if (domain->type == IOMMU_DOMAIN_DMA_FQ && iommu_dma_init_fq(domain))
-		domain->type = IOMMU_DOMAIN_DMA;
+	if (domain->type == IOMMU_DOMAIN_DMA_FQ) {
+		/* Expensive shadowing IOTLB flushes require some tuning */
+		if (dev->iommu->shadow_on_flush)
+			cookie->options.flags |= IOMMU_DMA_OPTS_SINGLE_QUEUE;
+
+		/* If the FQ fails we can simply fall back to strict mode */
+		if (iommu_dma_init_fq(domain)) {
+			domain->type = IOMMU_DOMAIN_DMA;
+			if (dev->iommu->shadow_on_flush)
+				cookie->options.flags &= ~IOMMU_DMA_OPTS_SINGLE_QUEUE;
+		}
+	}
 
 	ret = iova_reserve_iommu_regions(dev, domain);
 
diff --git a/drivers/iommu/iommu.c b/drivers/iommu/iommu.c
index 51f816367205..f1dcfa3f1a1b 100644
--- a/drivers/iommu/iommu.c
+++ b/drivers/iommu/iommu.c
@@ -2440,17 +2440,8 @@  int iommu_map(struct iommu_domain *domain, unsigned long iova,
 		return -EINVAL;
 
 	ret = __iommu_map(domain, iova, paddr, size, prot, gfp);
-	if (ret == 0 && ops->iotlb_sync_map) {
-		ret = ops->iotlb_sync_map(domain, iova, size);
-		if (ret)
-			goto out_err;
-	}
-
-	return ret;
-
-out_err:
-	/* undo mappings already done */
-	iommu_unmap(domain, iova, size);
+	if (ret == 0 && ops->iotlb_sync_map)
+		ops->iotlb_sync_map(domain, iova, size);
 
 	return ret;
 }
@@ -2591,11 +2582,8 @@  ssize_t iommu_map_sg(struct iommu_domain *domain, unsigned long iova,
 			sg = sg_next(sg);
 	}
 
-	if (ops->iotlb_sync_map) {
-		ret = ops->iotlb_sync_map(domain, iova, mapped);
-		if (ret)
-			goto out_err;
-	}
+	if (ops->iotlb_sync_map)
+		ops->iotlb_sync_map(domain, iova, mapped);
 	return mapped;
 
 out_err:
diff --git a/drivers/iommu/s390-iommu.c b/drivers/iommu/s390-iommu.c
index 71b177910eec..7b58ffda372c 100644
--- a/drivers/iommu/s390-iommu.c
+++ b/drivers/iommu/s390-iommu.c
@@ -467,6 +467,9 @@  static struct iommu_device *s390_iommu_probe_device(struct device *dev)
 	if (zdev->end_dma > ZPCI_TABLE_SIZE_RT - 1)
 		zdev->end_dma = ZPCI_TABLE_SIZE_RT - 1;
 
+	if (zdev->tlb_refresh)
+		dev->iommu->shadow_on_flush = 1;
+
 	return &zdev->iommu_dev;
 }
 
diff --git a/include/linux/iommu.h b/include/linux/iommu.h
index 58891eddc2c4..258e6f238ffa 100644
--- a/include/linux/iommu.h
+++ b/include/linux/iommu.h
@@ -403,6 +403,7 @@  struct iommu_fault_param {
  * @priv:	 IOMMU Driver private data
  * @max_pasids:  number of PASIDs this device can consume
  * @attach_deferred: the dma domain attachment is deferred
+ * @shadow_on_flush: IOTLB flushes are used to sync shadow tables
  *
  * TODO: migrate other per device data pointers under iommu_dev_data, e.g.
  *	struct iommu_group	*iommu_group;
@@ -416,6 +417,7 @@  struct dev_iommu {
 	void				*priv;
 	u32				max_pasids;
 	u32				attach_deferred:1;
+	u32				shadow_on_flush:1;
 };
 
 int iommu_device_register(struct iommu_device *iommu,