linux-kernel - Re: [PATCH v2] tee: convert get_user_pages() --> pin_user

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Date:   Tue, 26 May 2020 10:48:50 +0200
From:   Jens Wiklander <jens.wiklander@...aro.org>
To:     John Hubbard <jhubbard@...dia.com>
Cc:     LKML <linux-kernel@...r.kernel.org>,
        Sumit Semwal <sumit.semwal@...aro.org>,
        "tee-dev @ lists . linaro . org" <tee-dev@...ts.linaro.org>,
        linux-media@...r.kernel.org,
        DRI Development <dri-devel@...ts.freedesktop.org>,
        linaro-mm-sig@...ts.linaro.org
Subject: Re: [PATCH v2] tee: convert get_user_pages() --> pin_user_pages()

Hi John,

On Tue, May 26, 2020 at 1:32 AM John Hubbard <jhubbard@...dia.com> wrote:
>
> 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>
> ---
>
> Hi,
>
> This fixes the typo ("convert convert") in the subject line, but
> otherwise no changes.
>
> thanks,
> John Hubbard
> NVIDIA
>
>
>  drivers/tee/tee_shm.c | 12 +++---------
>  1 file changed, 3 insertions(+), 9 deletions(-)

Looks good. I've tested this on a HiKey 620 board, no regressions. I'm
picking up this patch.

Thanks,
Jens

>
> 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
>