[RFC PATCH V2 4/4] powerpc/mm/iommu: Allow migration of cma allocated pages during mm_iommu_get

[Aneesh Kumar K.V]

Current code doesn't do page migration if the page allocated is a compound page.
With HugeTLB migration support, we can end up allocating hugetlb pages from
CMA region. Also THP pages can be allocated from CMA region. This patch updates
the code to handle compound pages correctly.

This use the new helper get_user_pages_cma_migrate. It does one get_user_pages
with right count, instead of doing one get_user_pages per page. That avoids
reading page table multiple times.

The patch also convert the hpas member of mm_iommu_table_group_mem_t to a union.
We use the same storage location to store pointers to struct page. We cannot
update alll the code path use struct page *, because we access hpas in real mode
and we can't do that struct page * to pfn conversion in real mode.

Signed-off-by: Aneesh Kumar K.V <aneesh.kumar@xxxxxxxxxxxxx>
---
 arch/powerpc/mm/mmu_context_iommu.c | 124 +++++++++-------------------
 1 file changed, 37 insertions(+), 87 deletions(-)

diff --git a/arch/powerpc/mm/mmu_context_iommu.c b/arch/powerpc/mm/mmu_context_iommu.c
index f472965f7638..607acd03ab06 100644
--- a/arch/powerpc/mm/mmu_context_iommu.c
+++ b/arch/powerpc/mm/mmu_context_iommu.c
@@ -20,6 +20,7 @@
 #include <linux/swap.h>
 #include <asm/mmu_context.h>
 #include <asm/pte-walk.h>
+#include <linux/mm_inline.h>
 
 static DEFINE_MUTEX(mem_list_mutex);
 
@@ -30,8 +31,18 @@ struct mm_iommu_table_group_mem_t {
 	atomic64_t mapped;
 	unsigned int pageshift;
 	u64 ua;			/* userspace address */
-	u64 entries;		/* number of entries in hpas[] */
-	u64 *hpas;		/* vmalloc'ed */
+	u64 entries;		/* number of entries in hpages[] */
+	/*
+	 * in mm_iommu_get we temporarily use this to store
+	 * struct page address.
+	 *
+	 * We need to convert ua to hpa in real mode. Make it
+	 * simpler by storing physicall address.
+	 */
+	union {
+		struct page **hpages;	/* vmalloc'ed */
+		phys_addr_t *hpas;
+	};
 };
 
 static long mm_iommu_adjust_locked_vm(struct mm_struct *mm,
@@ -74,63 +85,12 @@ bool mm_iommu_preregistered(struct mm_struct *mm)
 }
 EXPORT_SYMBOL_GPL(mm_iommu_preregistered);
 
-/*
- * Taken from alloc_migrate_target with changes to remove CMA allocations
- */
-struct page *new_iommu_non_cma_page(struct page *page, unsigned long private)
-{
-	gfp_t gfp_mask = GFP_USER;
-	struct page *new_page;
-
-	if (PageCompound(page))
-		return NULL;
-
-	if (PageHighMem(page))
-		gfp_mask |= __GFP_HIGHMEM;
-
-	/*
-	 * We don't want the allocation to force an OOM if possibe
-	 */
-	new_page = alloc_page(gfp_mask | __GFP_NORETRY | __GFP_NOWARN);
-	return new_page;
-}
-
-static int mm_iommu_move_page_from_cma(struct page *page)
-{
-	int ret = 0;
-	LIST_HEAD(cma_migrate_pages);
-
-	/* Ignore huge pages for now */
-	if (PageCompound(page))
-		return -EBUSY;
-
-	lru_add_drain();
-	ret = isolate_lru_page(page);
-	if (ret)
-		return ret;
-
-	list_add(&page->lru, &cma_migrate_pages);
-	put_page(page); /* Drop the gup reference */
-
-	ret = migrate_pages(&cma_migrate_pages, new_iommu_non_cma_page,
-				NULL, 0, MIGRATE_SYNC, MR_CONTIG_RANGE);
-	if (ret) {
-		if (!list_empty(&cma_migrate_pages))
-			putback_movable_pages(&cma_migrate_pages);
-	}
-
-	return 0;
-}
-
 long mm_iommu_get(struct mm_struct *mm, unsigned long ua, unsigned long entries,
 		struct mm_iommu_table_group_mem_t **pmem)
 {
 	struct mm_iommu_table_group_mem_t *mem;
-	long i, j, ret = 0, locked_entries = 0;
+	long i, ret = 0, locked_entries = 0;
 	unsigned int pageshift;
-	unsigned long flags;
-	unsigned long cur_ua;
-	struct page *page = NULL;
 
 	mutex_lock(&mem_list_mutex);
 
@@ -177,47 +137,37 @@ long mm_iommu_get(struct mm_struct *mm, unsigned long ua, unsigned long entries,
 		goto unlock_exit;
 	}
 
+	ret = get_user_pages_cma_migrate(ua, entries, 1, mem->hpages);
+	if (ret != entries) {
+		/* free the reference taken */
+		for (i = 0; i < ret; i++)
+			put_page(mem->hpages[i]);
+
+		vfree(mem->hpas);
+		kfree(mem);
+		ret = -EFAULT;
+		goto unlock_exit;
+	} else
+		ret = 0;
+
+	pageshift = PAGE_SHIFT;
 	for (i = 0; i < entries; ++i) {
-		cur_ua = ua + (i << PAGE_SHIFT);
-		if (1 != get_user_pages_fast(cur_ua,
-					1/* pages */, 1/* iswrite */, &page)) {
-			ret = -EFAULT;
-			for (j = 0; j < i; ++j)
-				put_page(pfn_to_page(mem->hpas[j] >>
-						PAGE_SHIFT));
-			vfree(mem->hpas);
-			kfree(mem);
-			goto unlock_exit;
-		}
+		struct page *page = mem->hpages[i];
 		/*
-		 * If we get a page from the CMA zone, since we are going to
-		 * be pinning these entries, we might as well move them out
-		 * of the CMA zone if possible. NOTE: faulting in + migration
-		 * can be expensive. Batching can be considered later
+		 * Allow to use larger than 64k IOMMU pages. Only do that
+		 * if we are backed by hugetlb.
 		 */
-		if (is_migrate_cma_page(page)) {
-			if (mm_iommu_move_page_from_cma(page))
-				goto populate;
-			if (1 != get_user_pages_fast(cur_ua,
-						1/* pages */, 1/* iswrite */,
-						&page)) {
-				ret = -EFAULT;
-				for (j = 0; j < i; ++j)
-					put_page(pfn_to_page(mem->hpas[j] >>
-								PAGE_SHIFT));
-				vfree(mem->hpas);
-				kfree(mem);
-				goto unlock_exit;
-			}
-		}
-populate:
-		pageshift = PAGE_SHIFT;
-		if (mem->pageshift > PAGE_SHIFT && PageHuge(page)) {
+		if ((mem->pageshift > PAGE_SHIFT) && PageHuge(page)) {
 			struct page *head = compound_head(page);
 			pageshift = compound_order(head) + PAGE_SHIFT;
 		}
 		mem->pageshift = min(mem->pageshift, pageshift);
+		/*
+		 * We don't need struct page reference any more, switch
+		 * physicall address.
+		 */
 		mem->hpas[i] = page_to_pfn(page) << PAGE_SHIFT;
+
 	}
 
 	atomic64_set(&mem->mapped, 1);
-- 
2.17.1