linux-kernel - Re: [RFC PATCH] xen/privcmd: Convert get_user_pages*() to pin_user

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Date:   Wed, 17 Jun 2020 13:57:29 -0400
From:   Boris Ostrovsky <boris.ostrovsky@...cle.com>
To:     Souptick Joarder <jrdr.linux@...il.com>, jgross@...e.com,
        sstabellini@...nel.org
Cc:     xen-devel@...ts.xenproject.org, linux-kernel@...r.kernel.org,
        John Hubbard <jhubbard@...dia.com>, paul@....org
Subject: Re: [RFC PATCH] xen/privcmd: Convert get_user_pages*() to
 pin_user_pages*()

On 6/16/20 11:14 PM, Souptick Joarder wrote:
> In 2019, we introduced pin_user_pages*() and now we are converting
> get_user_pages*() to the new API as appropriate. [1] & [2] could
> be referred for more information.
>
> [1] Documentation/core-api/pin_user_pages.rst
>
> [2] "Explicit pinning of user-space pages":
>         https://lwn.net/Articles/807108/
>
> Signed-off-by: Souptick Joarder <jrdr.linux@...il.com>
> Cc: John Hubbard <jhubbard@...dia.com>
> ---
> Hi,
>
> I have compile tested this patch but unable to run-time test,
> so any testing help is much appriciated.
>
> Also have a question, why the existing code is not marking the
> pages dirty (since it did FOLL_WRITE) ?


Indeed, seems to me it should. Paul?


>
>  drivers/xen/privcmd.c | 7 ++-----
>  1 file changed, 2 insertions(+), 5 deletions(-)
>
> diff --git a/drivers/xen/privcmd.c b/drivers/xen/privcmd.c
> index a250d11..543739e 100644
> --- a/drivers/xen/privcmd.c
> +++ b/drivers/xen/privcmd.c
> @@ -594,7 +594,7 @@ static int lock_pages(
>  		if (requested > nr_pages)
>  			return -ENOSPC;
>  
> -		pinned = get_user_pages_fast(
> +		pinned = pin_user_pages_fast(
>  			(unsigned long) kbufs[i].uptr,
>  			requested, FOLL_WRITE, pages);
>  		if (pinned < 0)
> @@ -614,10 +614,7 @@ static void unlock_pages(struct page *pages[], unsigned int nr_pages)
>  	if (!pages)
>  		return;
>  
> -	for (i = 0; i < nr_pages; i++) {
> -		if (pages[i])
> -			put_page(pages[i]);
> -	}
> +	unpin_user_pages(pages, nr_pages);


Why are you no longer checking for valid pages?


-boris