[PATCH RFT v2 1/4] vpda: try to fix the potential crash due to misusing __GFP_NOFAIL

[Barry Song <21cnbao@gmail.com>]

From: Barry Song <v-songbaohua@oppo.com>

mm doesn't support non-blockable __GFP_NOFAIL allocation. Because
__GFP_NOFAIL without direct reclamation may just result in a busy
loop within non-sleepable contexts.

static inline struct page *
__alloc_pages_slowpath(gfp_t gfp_mask, unsigned int order,
                                                struct alloc_context *ac)
{
        ...
        /*
         * Make sure that __GFP_NOFAIL request doesn't leak out and make sure
         * we always retry
         */
        if (gfp_mask & __GFP_NOFAIL) {
                /*
                 * All existing users of the __GFP_NOFAIL are blockable, so warn
                 * of any new users that actually require GFP_NOWAIT
                 */
                if (WARN_ON_ONCE_GFP(!can_direct_reclaim, gfp_mask))
                        goto fail;
                ...
        }
        ...
fail:
        warn_alloc(gfp_mask, ac->nodemask,
                        "page allocation failure: order:%u", order);
got_pg:
        return page;
}

Let's move the memory allocation out of the atomic context and use
the normal sleepable context to get pages.

[RFT]: This has only been compile-tested; I'd prefer if the VDPA maintainers
handles it.

Cc: "Michael S. Tsirkin" <mst@redhat.com>
Cc: Jason Wang <jasowang@redhat.com>
Cc: Xuan Zhuo <xuanzhuo@linux.alibaba.com>
Cc: "Eugenio Pérez" <eperezma@redhat.com>
Cc: Maxime Coquelin <maxime.coquelin@redhat.com>
Signed-off-by: Barry Song <v-songbaohua@oppo.com>
---
 drivers/vdpa/vdpa_user/iova_domain.c | 31 +++++++++++++++++++++++-----
 drivers/vdpa/vdpa_user/iova_domain.h |  5 ++++-
 drivers/vdpa/vdpa_user/vduse_dev.c   |  4 +++-
 3 files changed, 33 insertions(+), 7 deletions(-)

diff --git a/drivers/vdpa/vdpa_user/iova_domain.c b/drivers/vdpa/vdpa_user/iova_domain.c
index 791d38d6284c..9318f059a8b5 100644
--- a/drivers/vdpa/vdpa_user/iova_domain.c
+++ b/drivers/vdpa/vdpa_user/iova_domain.c
@@ -283,7 +283,23 @@ int vduse_domain_add_user_bounce_pages(struct vduse_iova_domain *domain,
 	return ret;
 }
 
-void vduse_domain_remove_user_bounce_pages(struct vduse_iova_domain *domain)
+struct page **vduse_domain_alloc_pages_to_remove_bounce(struct vduse_iova_domain *domain)
+{
+	struct page **pages;
+	unsigned long count, i;
+
+	if (!domain->user_bounce_pages)
+		return NULL;
+
+	count = domain->bounce_size >> PAGE_SHIFT;
+	pages = kmalloc_array(count, sizeof(*pages), GFP_KERNEL | __GFP_NOFAIL);
+	for (i = 0; i < count; i++)
+		pages[i] = alloc_page(GFP_KERNEL | __GFP_NOFAIL);
+
+	return pages;
+}
+
+void vduse_domain_remove_user_bounce_pages(struct vduse_iova_domain *domain, struct page **pages)
 {
 	struct vduse_bounce_map *map;
 	unsigned long i, count;
@@ -294,15 +310,16 @@ void vduse_domain_remove_user_bounce_pages(struct vduse_iova_domain *domain)
 
 	count = domain->bounce_size >> PAGE_SHIFT;
 	for (i = 0; i < count; i++) {
-		struct page *page = NULL;
+		struct page *page = pages[i];
 
 		map = &domain->bounce_maps[i];
-		if (WARN_ON(!map->bounce_page))
+		if (WARN_ON(!map->bounce_page)) {
+			put_page(page);
 			continue;
+		}
 
 		/* Copy user page to kernel page if it's in use */
 		if (map->orig_phys != INVALID_PHYS_ADDR) {
-			page = alloc_page(GFP_ATOMIC | __GFP_NOFAIL);
 			memcpy_from_page(page_address(page),
 					 map->bounce_page, 0, PAGE_SIZE);
 		}
@@ -310,6 +327,7 @@ void vduse_domain_remove_user_bounce_pages(struct vduse_iova_domain *domain)
 		map->bounce_page = page;
 	}
 	domain->user_bounce_pages = false;
+	kfree(pages);
 out:
 	write_unlock(&domain->bounce_lock);
 }
@@ -543,10 +561,13 @@ static int vduse_domain_mmap(struct file *file, struct vm_area_struct *vma)
 static int vduse_domain_release(struct inode *inode, struct file *file)
 {
 	struct vduse_iova_domain *domain = file->private_data;
+	struct page **pages;
+
+	pages = vduse_domain_alloc_pages_to_remove_bounce(domain);
 
 	spin_lock(&domain->iotlb_lock);
 	vduse_iotlb_del_range(domain, 0, ULLONG_MAX);
-	vduse_domain_remove_user_bounce_pages(domain);
+	vduse_domain_remove_user_bounce_pages(domain, pages);
 	vduse_domain_free_kernel_bounce_pages(domain);
 	spin_unlock(&domain->iotlb_lock);
 	put_iova_domain(&domain->stream_iovad);
diff --git a/drivers/vdpa/vdpa_user/iova_domain.h b/drivers/vdpa/vdpa_user/iova_domain.h
index f92f22a7267d..17efa5555b3f 100644
--- a/drivers/vdpa/vdpa_user/iova_domain.h
+++ b/drivers/vdpa/vdpa_user/iova_domain.h
@@ -74,7 +74,10 @@ void vduse_domain_reset_bounce_map(struct vduse_iova_domain *domain);
 int vduse_domain_add_user_bounce_pages(struct vduse_iova_domain *domain,
 				       struct page **pages, int count);
 
-void vduse_domain_remove_user_bounce_pages(struct vduse_iova_domain *domain);
+void vduse_domain_remove_user_bounce_pages(struct vduse_iova_domain *domain,
+					   struct page **pages);
+
+struct page **vduse_domain_alloc_pages_to_remove_bounce(struct vduse_iova_domain *domain);
 
 void vduse_domain_destroy(struct vduse_iova_domain *domain);
 
diff --git a/drivers/vdpa/vdpa_user/vduse_dev.c b/drivers/vdpa/vdpa_user/vduse_dev.c
index 7ae99691efdf..5d8d5810df57 100644
--- a/drivers/vdpa/vdpa_user/vduse_dev.c
+++ b/drivers/vdpa/vdpa_user/vduse_dev.c
@@ -1030,6 +1030,7 @@ static int vduse_dev_queue_irq_work(struct vduse_dev *dev,
 static int vduse_dev_dereg_umem(struct vduse_dev *dev,
 				u64 iova, u64 size)
 {
+	struct page **pages;
 	int ret;
 
 	mutex_lock(&dev->mem_lock);
@@ -1044,7 +1045,8 @@ static int vduse_dev_dereg_umem(struct vduse_dev *dev,
 	if (dev->umem->iova != iova || size != dev->domain->bounce_size)
 		goto unlock;
 
-	vduse_domain_remove_user_bounce_pages(dev->domain);
+	pages = vduse_domain_alloc_pages_to_remove_bounce(dev->domain);
+	vduse_domain_remove_user_bounce_pages(dev->domain, pages);
 	unpin_user_pages_dirty_lock(dev->umem->pages,
 				    dev->umem->npages, true);
 	atomic64_sub(dev->umem->npages, &dev->umem->mm->pinned_vm);
-- 
2.34.1