[RFC PATCH v1 6/7] iommu/arm: ipmmu-vmsa: Deallocate page table asynchronously

[Oleksandr Tyshchenko <olekstysh@gmail.com>]

From: Oleksandr Tyshchenko <oleksandr_tyshchenko@epam.com>

This is the PoC how to optimize page table deallocation sequence
by splitting it into separate chunks.
Use iommu_pt_cleanup_list to queue pages that need to be handled and
freed next time. Use free_page_table platform callback to dequeue
pages.

Signed-off-by: Oleksandr Tyshchenko <oleksandr_tyshchenko@epam.com>
CC: Julien Grall <julien.grall@arm.com>
CC: Stefano Stabellini <sstabellini@kernel.org>
---
 xen/drivers/passthrough/arm/io-pgtable-arm.c | 94 +++++++++++++++++++++++++---
 xen/drivers/passthrough/arm/io-pgtable.c     |  5 +-
 xen/drivers/passthrough/arm/io-pgtable.h     |  4 +-
 xen/drivers/passthrough/arm/ipmmu-vmsa.c     | 33 ++++++++--
 4 files changed, 119 insertions(+), 17 deletions(-)

diff --git a/xen/drivers/passthrough/arm/io-pgtable-arm.c b/xen/drivers/passthrough/arm/io-pgtable-arm.c
index c98caa3..7673fda 100644
--- a/xen/drivers/passthrough/arm/io-pgtable-arm.c
+++ b/xen/drivers/passthrough/arm/io-pgtable-arm.c
@@ -254,6 +254,10 @@ struct arm_lpae_io_pgtable {
 
 	/* Xen: We deal with domain pages. */
 	struct page_info	*pgd;
+	/* Xen: To indicate that deallocation sequence is in progress. */
+	bool_t				cleanup;
+	/* Xen: To count allocated domain pages. */
+	unsigned int		page_count;
 };
 
 typedef u64 arm_lpae_iopte;
@@ -329,7 +333,7 @@ static void __arm_lpae_set_pte(arm_lpae_iopte *ptep, arm_lpae_iopte pte,
 #endif
 
 static struct page_info *__arm_lpae_alloc_pages(size_t size, gfp_t gfp,
-				    struct io_pgtable_cfg *cfg)
+				    struct arm_lpae_io_pgtable *data)
 {
 	struct page_info *pages;
 	unsigned int order = get_order_from_bytes(size);
@@ -342,15 +346,21 @@ static struct page_info *__arm_lpae_alloc_pages(size_t size, gfp_t gfp,
 	for (i = 0; i < (1 << order); i ++)
 		clear_and_clean_page(pages + i);
 
+	data->page_count += (1<<order);
+
 	return pages;
 }
 
 static void __arm_lpae_free_pages(struct page_info *pages, size_t size,
-				  struct io_pgtable_cfg *cfg)
+				  struct arm_lpae_io_pgtable *data)
 {
 	unsigned int order = get_order_from_bytes(size);
 
+	BUG_ON((int)data->page_count <= 0);
+
 	free_domheap_pages(pages, order);
+
+	data->page_count -= (1<<order);
 }
 
 static void __arm_lpae_set_pte(arm_lpae_iopte *ptep, arm_lpae_iopte pte,
@@ -434,7 +444,7 @@ static int __arm_lpae_map(struct arm_lpae_io_pgtable *data, unsigned long iova,
 	pte = *ptep;
 	if (!pte) {
 		page = __arm_lpae_alloc_pages(ARM_LPAE_GRANULE(data),
-					       GFP_ATOMIC, cfg);
+					       GFP_ATOMIC, data);
 		if (!page)
 			return -ENOMEM;
 
@@ -526,6 +536,46 @@ static int arm_lpae_map(struct io_pgtable_ops *ops, unsigned long iova,
 	return ret;
 }
 
+static void __arm_lpae_free_pgtable(struct arm_lpae_io_pgtable *data, int lvl,
+				    struct page_info *page);
+
+/*
+ * TODO: We have reused unused at the moment "page->pad" variable for
+ * storing "data" pointer we need during deallocation sequence. The current
+ * free_page_table platform callback carries the only one "page" argument.
+ * To perform required calculations with the current (generic) allocator
+ * implementation we are highly interested in the following fields:
+ * - data->levels
+ * - data->pg_shift
+ * - data->pgd_size
+ * But, this necessity might be avoided if we integrate allocator code with
+ * IPMMU-VMSA driver. And these variables will turn into the
+ * corresponding #define-s.
+ */
+static void __arm_lpae_free_next_pgtable(struct arm_lpae_io_pgtable *data,
+				    int lvl, struct page_info *page)
+{
+	if (!data->cleanup) {
+		/*
+		 * We are here during normal page table maintenance. Just call
+		 * __arm_lpae_free_pgtable(), what we actually had to call.
+		 */
+		__arm_lpae_free_pgtable(data, lvl, page);
+	} else {
+		/*
+		 * The page table deallocation sequence is in progress. Use some fields
+		 * in struct page_info to pass arguments we will need during handling
+		 * this page back. Queue page to list.
+		 */
+		PFN_ORDER(page) = lvl;
+		page->pad = (u64)&data->iop.ops;
+
+		spin_lock(&iommu_pt_cleanup_lock);
+		page_list_add_tail(page, &iommu_pt_cleanup_list);
+		spin_unlock(&iommu_pt_cleanup_lock);
+	}
+}
+
 /* Xen: We deal with domain pages. */
 static void __arm_lpae_free_pgtable(struct arm_lpae_io_pgtable *data, int lvl,
 				    struct page_info *page)
@@ -553,19 +603,41 @@ static void __arm_lpae_free_pgtable(struct arm_lpae_io_pgtable *data, int lvl,
 		if (!pte || iopte_leaf(pte, lvl))
 			continue;
 
-		__arm_lpae_free_pgtable(data, lvl + 1, iopte_deref(pte, data));
+		__arm_lpae_free_next_pgtable(data, lvl + 1, iopte_deref(pte, data));
 	}
 
 	unmap_domain_page(start);
-	__arm_lpae_free_pages(page, table_size, &data->iop.cfg);
+	__arm_lpae_free_pages(page, table_size, data);
 }
 
-static void arm_lpae_free_pgtable(struct io_pgtable *iop)
+/*
+ * We added extra "page" argument since we want to know what page is processed
+ * at the moment and should be freed.
+ * */
+static void arm_lpae_free_pgtable(struct io_pgtable *iop, struct page_info *page)
 {
 	struct arm_lpae_io_pgtable *data = io_pgtable_to_data(iop);
+	int lvl;
 
-	__arm_lpae_free_pgtable(data, ARM_LPAE_START_LVL(data), data->pgd);
-	kfree(data);
+	if (!data->cleanup) {
+		/* Start page table deallocation sequence from the first level. */
+		data->cleanup = true;
+		lvl = ARM_LPAE_START_LVL(data);
+	} else {
+		/* Retrieve the level to continue deallocation sequence from. */
+		lvl = PFN_ORDER(page);
+		PFN_ORDER(page) = 0;
+		page->pad = 0;
+	}
+
+	__arm_lpae_free_pgtable(data, lvl, page);
+
+	/*
+	 * Seems, we have already deallocated all pages, so it is time
+	 * to release unfreed resource.
+	 */
+	if (!data->page_count)
+		kfree(data);
 }
 
 /* Xen: We deal with domain pages. */
@@ -889,8 +961,12 @@ arm_64_lpae_alloc_pgtable_s1(struct io_pgtable_cfg *cfg, void *cookie)
 	cfg->arm_lpae_s1_cfg.mair[0] = reg;
 	cfg->arm_lpae_s1_cfg.mair[1] = 0;
 
+	/* Just to be sure */
+	data->cleanup = false;
+	data->page_count = 0;
+
 	/* Looking good; allocate a pgd */
-	data->pgd = __arm_lpae_alloc_pages(data->pgd_size, GFP_KERNEL, cfg);
+	data->pgd = __arm_lpae_alloc_pages(data->pgd_size, GFP_KERNEL, data);
 	if (!data->pgd)
 		goto out_free_data;
 
diff --git a/xen/drivers/passthrough/arm/io-pgtable.c b/xen/drivers/passthrough/arm/io-pgtable.c
index bfc7020..e25d731 100644
--- a/xen/drivers/passthrough/arm/io-pgtable.c
+++ b/xen/drivers/passthrough/arm/io-pgtable.c
@@ -77,7 +77,7 @@ struct io_pgtable_ops *alloc_io_pgtable_ops(enum io_pgtable_fmt fmt,
  * It is the IOMMU driver's responsibility to ensure that the page table
  * is no longer accessible to the walker by this point.
  */
-void free_io_pgtable_ops(struct io_pgtable_ops *ops)
+void free_io_pgtable_ops(struct io_pgtable_ops *ops, struct page_info *page)
 {
 	struct io_pgtable *iop;
 
@@ -86,5 +86,6 @@ void free_io_pgtable_ops(struct io_pgtable_ops *ops)
 
 	iop = container_of(ops, struct io_pgtable, ops);
 	io_pgtable_tlb_flush_all(iop);
-	io_pgtable_init_table[iop->fmt]->free(iop);
+	iop->cookie = NULL;
+	io_pgtable_init_table[iop->fmt]->free(iop, page);
 }
diff --git a/xen/drivers/passthrough/arm/io-pgtable.h b/xen/drivers/passthrough/arm/io-pgtable.h
index fb81fcf..df0e21b 100644
--- a/xen/drivers/passthrough/arm/io-pgtable.h
+++ b/xen/drivers/passthrough/arm/io-pgtable.h
@@ -144,7 +144,7 @@ struct io_pgtable_ops *alloc_io_pgtable_ops(enum io_pgtable_fmt fmt,
  *
  * @ops: The ops returned from alloc_io_pgtable_ops.
  */
-void free_io_pgtable_ops(struct io_pgtable_ops *ops);
+void free_io_pgtable_ops(struct io_pgtable_ops *ops, struct page_info *page);
 
 
 /*
@@ -201,7 +201,7 @@ static inline void io_pgtable_tlb_sync(struct io_pgtable *iop)
  */
 struct io_pgtable_init_fns {
 	struct io_pgtable *(*alloc)(struct io_pgtable_cfg *cfg, void *cookie);
-	void (*free)(struct io_pgtable *iop);
+	void (*free)(struct io_pgtable *iop, struct page_info *page);
 };
 
 extern struct io_pgtable_init_fns io_pgtable_arm_32_lpae_s1_init_fns;
diff --git a/xen/drivers/passthrough/arm/ipmmu-vmsa.c b/xen/drivers/passthrough/arm/ipmmu-vmsa.c
index e54b507..2a04800 100644
--- a/xen/drivers/passthrough/arm/ipmmu-vmsa.c
+++ b/xen/drivers/passthrough/arm/ipmmu-vmsa.c
@@ -708,8 +708,8 @@ static void ipmmu_tlb_flush_all(void *cookie)
 {
 	struct ipmmu_vmsa_domain *domain = cookie;
 
-	/* Xen: Just return if context_id has non-existent value */
-	if (domain->context_id >= domain->root->num_ctx)
+	/* Xen: Just return if context is absent or context_id has non-existent value */
+	if (!domain || domain->context_id >= domain->root->num_ctx)
 		return;
 
 	ipmmu_tlb_invalidate(domain);
@@ -796,7 +796,9 @@ static int ipmmu_domain_init_context(struct ipmmu_vmsa_domain *domain)
 	 */
 	ret = ipmmu_domain_allocate_context(domain->root, domain);
 	if (ret < 0) {
-		free_io_pgtable_ops(domain->iop);
+		/* Pass root page table for this domain as an argument. */
+		free_io_pgtable_ops(domain->iop,
+				maddr_to_page(domain->cfg.arm_lpae_s1_cfg.ttbr[0]));
 		return ret;
 	}
 
@@ -2193,7 +2195,12 @@ static void ipmmu_vmsa_destroy_domain(struct iommu_domain *io_domain)
 		 * been detached.
 		 */
 		ipmmu_domain_destroy_context(domain);
-		free_io_pgtable_ops(domain->iop);
+		/*
+		 * Pass root page table for this domain as an argument.
+		 * This call will lead to start deallocation sequence.
+		 */
+		free_io_pgtable_ops(domain->iop,
+				maddr_to_page(domain->cfg.arm_lpae_s1_cfg.ttbr[0]));
 	}
 
 	kfree(domain);
@@ -2383,6 +2390,17 @@ static int ipmmu_vmsa_domain_init(struct domain *d, bool use_iommu)
 	return 0;
 }
 
+/*
+ * Seems, there is one more page we need to process. So, retrieve
+ * the pointer and go on deallocation sequence.
+ */
+static void ipmmu_vmsa_free_page_table(struct page_info *page)
+{
+	struct io_pgtable_ops *ops = (struct io_pgtable_ops *)page->pad;
+
+	free_io_pgtable_ops(ops, page);
+}
+
 static void __hwdom_init ipmmu_vmsa_hwdom_init(struct domain *d)
 {
 }
@@ -2404,6 +2422,12 @@ static void ipmmu_vmsa_domain_teardown(struct domain *d)
 	ASSERT(list_empty(&xen_domain->contexts));
 	xfree(xen_domain);
 	dom_iommu(d)->arch.priv = NULL;
+	/*
+	 * After this point we have all domain resources deallocated, except
+	 * page table which we will deallocate asynchronously. The IOMMU code
+	 * provides us with iommu_pt_cleanup_list and free_page_table platform
+	 * callback what we actually going to use.
+	 */
 }
 
 static int __must_check ipmmu_vmsa_map_pages(struct domain *d,
@@ -2462,6 +2486,7 @@ static void ipmmu_vmsa_dump_p2m_table(struct domain *d)
 static const struct iommu_ops ipmmu_vmsa_iommu_ops = {
 	.init = ipmmu_vmsa_domain_init,
 	.hwdom_init = ipmmu_vmsa_hwdom_init,
+	.free_page_table = ipmmu_vmsa_free_page_table,
 	.teardown = ipmmu_vmsa_domain_teardown,
 	.iotlb_flush = ipmmu_vmsa_iotlb_flush,
 	.assign_device = ipmmu_vmsa_assign_dev,
-- 
2.7.4


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