linux-kernel - [PATCH] tee: convert convert get_user_pages() --> pin_user

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Message-ID: <20200519051850.2845561-1-jhubbard@nvidia.com>
Date:   Mon, 18 May 2020 22:18:50 -0700
From:   John Hubbard <jhubbard@...dia.com>
To:     LKML <linux-kernel@...r.kernel.org>
CC:     John Hubbard <jhubbard@...dia.com>,
        Jens Wiklander <jens.wiklander@...aro.org>,
        Sumit Semwal <sumit.semwal@...aro.org>,
        <tee-dev@...ts.linaro.org>, <linux-media@...r.kernel.org>,
        <dri-devel@...ts.freedesktop.org>, <linaro-mm-sig@...ts.linaro.org>
Subject: [PATCH] tee: convert convert get_user_pages() --> pin_user_pages()

This code was using get_user_pages*(), in a "Case 2" scenario
(DMA/RDMA), using the categorization from [1]. That means that it's
time to convert the get_user_pages*() + put_page() calls to
pin_user_pages*() + unpin_user_pages() calls.

There is some helpful background in [2]: basically, this is a small
part of fixing a long-standing disconnect between pinning pages, and
file systems' use of those pages.

[1] Documentation/core-api/pin_user_pages.rst

[2] "Explicit pinning of user-space pages":
    https://lwn.net/Articles/807108/

Cc: Jens Wiklander <jens.wiklander@...aro.org>
Cc: Sumit Semwal <sumit.semwal@...aro.org>
Cc: tee-dev@...ts.linaro.org
Cc: linux-media@...r.kernel.org
Cc: dri-devel@...ts.freedesktop.org
Cc: linaro-mm-sig@...ts.linaro.org
Signed-off-by: John Hubbard <jhubbard@...dia.com>
---

Note that I have only compile-tested this patch, although that does
also include cross-compiling for a few other arches.

thanks,
John Hubbard
NVIDIA

 drivers/tee/tee_shm.c | 12 +++---------
 1 file changed, 3 insertions(+), 9 deletions(-)

diff --git a/drivers/tee/tee_shm.c b/drivers/tee/tee_shm.c
index bd679b72bd05..7dffc42d8d5a 100644
--- a/drivers/tee/tee_shm.c
+++ b/drivers/tee/tee_shm.c
@@ -31,16 +31,13 @@ static void tee_shm_release(struct tee_shm *shm)
 
 		poolm->ops->free(poolm, shm);
 	} else if (shm->flags & TEE_SHM_REGISTER) {
-		size_t n;
 		int rc = teedev->desc->ops->shm_unregister(shm->ctx, shm);
 
 		if (rc)
 			dev_err(teedev->dev.parent,
 				"unregister shm %p failed: %d", shm, rc);
 
-		for (n = 0; n < shm->num_pages; n++)
-			put_page(shm->pages[n]);
-
+		unpin_user_pages(shm->pages, shm->num_pages);
 		kfree(shm->pages);
 	}
 
@@ -226,7 +223,7 @@ struct tee_shm *tee_shm_register(struct tee_context *ctx, unsigned long addr,
 		goto err;
 	}
 
-	rc = get_user_pages_fast(start, num_pages, FOLL_WRITE, shm->pages);
+	rc = pin_user_pages_fast(start, num_pages, FOLL_WRITE, shm->pages);
 	if (rc > 0)
 		shm->num_pages = rc;
 	if (rc != num_pages) {
@@ -271,16 +268,13 @@ struct tee_shm *tee_shm_register(struct tee_context *ctx, unsigned long addr,
 	return shm;
 err:
 	if (shm) {
-		size_t n;
-
 		if (shm->id >= 0) {
 			mutex_lock(&teedev->mutex);
 			idr_remove(&teedev->idr, shm->id);
 			mutex_unlock(&teedev->mutex);
 		}
 		if (shm->pages) {
-			for (n = 0; n < shm->num_pages; n++)
-				put_page(shm->pages[n]);
+			unpin_user_pages(shm->pages, shm->num_pages);
 			kfree(shm->pages);
 		}
 	}
-- 
2.26.2