linux-kernel - Re: [PATCH v2 08/18] mm/process_vm_access: set FOLL_PIN via pin_user_pages

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Date:   Mon, 4 Nov 2019 12:41:55 -0500
From:   Jerome Glisse <jglisse@...hat.com>
To:     John Hubbard <jhubbard@...dia.com>
Cc:     Andrew Morton <akpm@...ux-foundation.org>,
        Al Viro <viro@...iv.linux.org.uk>,
        Alex Williamson <alex.williamson@...hat.com>,
        Benjamin Herrenschmidt <benh@...nel.crashing.org>,
        Björn Töpel <bjorn.topel@...el.com>,
        Christoph Hellwig <hch@...radead.org>,
        Dan Williams <dan.j.williams@...el.com>,
        Daniel Vetter <daniel@...ll.ch>,
        Dave Chinner <david@...morbit.com>,
        David Airlie <airlied@...ux.ie>,
        "David S . Miller" <davem@...emloft.net>,
        Ira Weiny <ira.weiny@...el.com>, Jan Kara <jack@...e.cz>,
        Jason Gunthorpe <jgg@...pe.ca>, Jens Axboe <axboe@...nel.dk>,
        Jonathan Corbet <corbet@....net>,
        Magnus Karlsson <magnus.karlsson@...el.com>,
        Mauro Carvalho Chehab <mchehab@...nel.org>,
        Michael Ellerman <mpe@...erman.id.au>,
        Michal Hocko <mhocko@...e.com>,
        Mike Kravetz <mike.kravetz@...cle.com>,
        Paul Mackerras <paulus@...ba.org>,
        Shuah Khan <shuah@...nel.org>,
        Vlastimil Babka <vbabka@...e.cz>, bpf@...r.kernel.org,
        dri-devel@...ts.freedesktop.org, kvm@...r.kernel.org,
        linux-block@...r.kernel.org, linux-doc@...r.kernel.org,
        linux-fsdevel@...r.kernel.org, linux-kselftest@...r.kernel.org,
        linux-media@...r.kernel.org, linux-rdma@...r.kernel.org,
        linuxppc-dev@...ts.ozlabs.org, netdev@...r.kernel.org,
        linux-mm@...ck.org, LKML <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH v2 08/18] mm/process_vm_access: set FOLL_PIN via
 pin_user_pages_remote()

On Sun, Nov 03, 2019 at 01:18:03PM -0800, John Hubbard wrote:
> Convert process_vm_access to use the new pin_user_pages_remote()
> call, which sets FOLL_PIN. Setting FOLL_PIN is now required for
> code that requires tracking of pinned pages.
> 
> Also, release the pages via put_user_page*().
> 
> Also, rename "pages" to "pinned_pages", as this makes for
> easier reading of process_vm_rw_single_vec().
> 
> Reviewed-by: Ira Weiny <ira.weiny@...el.com>
> Signed-off-by: John Hubbard <jhubbard@...dia.com>

Reviewed-by: Jérôme Glisse <jglisse@...hat.com>

> ---
>  mm/process_vm_access.c | 28 +++++++++++++++-------------
>  1 file changed, 15 insertions(+), 13 deletions(-)
> 
> diff --git a/mm/process_vm_access.c b/mm/process_vm_access.c
> index 357aa7bef6c0..fd20ab675b85 100644
> --- a/mm/process_vm_access.c
> +++ b/mm/process_vm_access.c
> @@ -42,12 +42,11 @@ static int process_vm_rw_pages(struct page **pages,
>  		if (copy > len)
>  			copy = len;
>  
> -		if (vm_write) {
> +		if (vm_write)
>  			copied = copy_page_from_iter(page, offset, copy, iter);
> -			set_page_dirty_lock(page);
> -		} else {
> +		else
>  			copied = copy_page_to_iter(page, offset, copy, iter);
> -		}
> +
>  		len -= copied;
>  		if (copied < copy && iov_iter_count(iter))
>  			return -EFAULT;
> @@ -96,7 +95,7 @@ static int process_vm_rw_single_vec(unsigned long addr,
>  		flags |= FOLL_WRITE;
>  
>  	while (!rc && nr_pages && iov_iter_count(iter)) {
> -		int pages = min(nr_pages, max_pages_per_loop);
> +		int pinned_pages = min(nr_pages, max_pages_per_loop);
>  		int locked = 1;
>  		size_t bytes;
>  
> @@ -106,14 +105,15 @@ static int process_vm_rw_single_vec(unsigned long addr,
>  		 * current/current->mm
>  		 */
>  		down_read(&mm->mmap_sem);
> -		pages = get_user_pages_remote(task, mm, pa, pages, flags,
> -					      process_pages, NULL, &locked);
> +		pinned_pages = pin_user_pages_remote(task, mm, pa, pinned_pages,
> +						     flags, process_pages,
> +						     NULL, &locked);
>  		if (locked)
>  			up_read(&mm->mmap_sem);
> -		if (pages <= 0)
> +		if (pinned_pages <= 0)
>  			return -EFAULT;
>  
> -		bytes = pages * PAGE_SIZE - start_offset;
> +		bytes = pinned_pages * PAGE_SIZE - start_offset;
>  		if (bytes > len)
>  			bytes = len;
>  
> @@ -122,10 +122,12 @@ static int process_vm_rw_single_vec(unsigned long addr,
>  					 vm_write);
>  		len -= bytes;
>  		start_offset = 0;
> -		nr_pages -= pages;
> -		pa += pages * PAGE_SIZE;
> -		while (pages)
> -			put_page(process_pages[--pages]);
> +		nr_pages -= pinned_pages;
> +		pa += pinned_pages * PAGE_SIZE;
> +
> +		/* If vm_write is set, the pages need to be made dirty: */
> +		put_user_pages_dirty_lock(process_pages, pinned_pages,
> +					  vm_write);
>  	}
>  
>  	return rc;
> -- 
> 2.23.0
>