RDMA/hns: Fix sg offset non-zero issue

When run perftest in many times, the system will report a BUG as follows:

   BUG: Bad rss-counter state mm:(____ptrval____) idx:0 val:-1
   BUG: Bad rss-counter state mm:(____ptrval____) idx:1 val:1

We tested with different kernel version and found it started from the the
following commit:

commit d10bcf94 ("RDMA/umem: Combine contiguous PAGE_SIZE regions in
SGEs")

In this commit, the sg->offset is always 0 when sg_set_page() is called in
ib_umem_get() and the drivers are not allowed to change the sgl, otherwise
it will get bad page descriptor when unfolding SGEs in __ib_umem_release()
as sg_page_count() will get wrong result while sgl->offset is not 0.

However, there is a weird sgl usage in the current hns driver, the driver
modified sg->offset after calling ib_umem_get(), which caused we iterate
past the wrong number of pages in for_each_sg_page iterator.

This patch fixes it by correcting the non-standard sgl usage found in the
hns_roce_db_map_user() function.

Fixes: d10bcf94 ("RDMA/umem: Combine contiguous PAGE_SIZE regions in SGEs")
Fixes: 0425e3e6 ("RDMA/hns: Support flush cqe for hip08 in kernel space")
Link: https://lore.kernel.org/r/1562808737-45723-1-git-send-email-oulijun@huawei.comSigned-off-by: Xi Wang <wangxi11@huawei.com>
Signed-off-by: Jason Gunthorpe <jgg@mellanox.com>

drivers/infiniband/hw/hns/hns_roce_db.c

@@ -12,13 +12,15 @@ int hns_roce_db_map_user(struct hns_roce_ucontext *context,
 			 struct ib_udata *udata, unsigned long virt,
 			 struct hns_roce_db *db)
 {
+	unsigned long page_addr = virt & PAGE_MASK;
 	struct hns_roce_user_db_page *page;
+	unsigned int offset;
 	int ret = 0;
 
 	mutex_lock(&context->page_mutex);
 
 	list_for_each_entry(page, &context->page_list, list)
-		if (page->user_virt == (virt & PAGE_MASK))
+		if (page->user_virt == page_addr)
 			goto found;
 
 	page = kmalloc(sizeof(*page), GFP_KERNEL);
@@ -28,8 +30,8 @@ int hns_roce_db_map_user(struct hns_roce_ucontext *context,
 	}
 
 	refcount_set(&page->refcount, 1);
-	page->user_virt = (virt & PAGE_MASK);
-	page->umem = ib_umem_get(udata, virt & PAGE_MASK, PAGE_SIZE, 0, 0);
+	page->user_virt = page_addr;
+	page->umem = ib_umem_get(udata, page_addr, PAGE_SIZE, 0, 0);
 	if (IS_ERR(page->umem)) {
 		ret = PTR_ERR(page->umem);
 		kfree(page);
@@ -39,10 +41,9 @@ int hns_roce_db_map_user(struct hns_roce_ucontext *context,
 	list_add(&page->list, &context->page_list);
 
 found:
-	db->dma = sg_dma_address(page->umem->sg_head.sgl) +
-		  (virt & ~PAGE_MASK);
-	page->umem->sg_head.sgl->offset = virt & ~PAGE_MASK;
-	db->virt_addr = sg_virt(page->umem->sg_head.sgl);
+	offset = virt - page_addr;
+	db->dma = sg_dma_address(page->umem->sg_head.sgl) + offset;
+	db->virt_addr = sg_virt(page->umem->sg_head.sgl) + offset;
 	db->u.user_page = page;
 	refcount_inc(&page->refcount);