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

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Date:   Mon, 24 Aug 2020 11:42:51 -0700
From:   John Hubbard <jhubbard@...dia.com>
To:     <jens.wiklander@...aro.org>
CC:     <arm@...nel.org>, <linux-arm-kernel@...ts.infradead.org>,
        <linux-kernel@...r.kernel.org>, <olof@...om.net>, <soc@...nel.org>,
        <tee-dev@...ts.linaro.org>, Sumit Semwal <sumit.semwal@...aro.org>,
        <linux-media@...r.kernel.org>, <dri-devel@...ts.freedesktop.org>,
        <linaro-mm-sig@...ts.linaro.org>
Subject: Re: [PATCH v2] tee: convert convert get_user_pages() -->
 pin_user_pages()

On 8/24/20 11:36 AM, John Hubbard 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>
> ---
> 
> OK, this should be indentical to v1 [1], but now rebased against
> Linux 5.9-rc2.
> 

...ohhh, wait, I should have read the earlier message from Jens more
carefully:

"The conflict isn't trivial, I guess we need to handle the different
types of pages differently when releasing them."

So it's not good to have a logically identical patch. argghhh. Let me see
how hard it is to track these memory types separately and handle the release
accordingly, just a sec.

Sorry about the false move here.

thanks,
-- 
John Hubbard
NVIDIA

> As before, I've compile-tested it again with a cross compiler, but that's
> the only testing I'm set up for with CONFIG_TEE.
> 
> [1] https://lore.kernel.org/r/20200519051850.2845561-1-jhubbard@nvidia.com
> 
> 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 827ac3d0fea9..3c29e6c3ebe8 100644
> --- a/drivers/tee/tee_shm.c
> +++ b/drivers/tee/tee_shm.c
> @@ -32,16 +32,13 @@ 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);
>   	}
>   
> @@ -228,7 +225,7 @@ struct tee_shm *tee_shm_register(struct tee_context *ctx, unsigned long addr,
>   	}
>   
>   	if (flags & TEE_SHM_USER_MAPPED) {
> -		rc = get_user_pages_fast(start, num_pages, FOLL_WRITE,
> +		rc = pin_user_pages_fast(start, num_pages, FOLL_WRITE,
>   					 shm->pages);
>   	} else {
>   		struct kvec *kiov;
> @@ -292,16 +289,13 @@ 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);
>   		}
>   	}
> 

v