Re: [PATCH 08/19] mm/process_vm_access: set FOLL_PIN via pin_user_pages_remote()

From: Ira Weiny <ira.weiny@intel.com>
To: John Hubbard <jhubbard@nvidia.com>
Cc: "Michal Hocko" <mhocko@suse.com>, "Jan Kara" <jack@suse.cz>,
	kvm@vger.kernel.org, linux-doc@vger.kernel.org,
	"David Airlie" <airlied@linux.ie>,
	"Dave Chinner" <david@fromorbit.com>,
	dri-devel@lists.freedesktop.org,
	LKML <linux-kernel@vger.kernel.org>,
	linux-mm@kvack.org, "Paul Mackerras" <paulus@samba.org>,
	linux-kselftest@vger.kernel.org, "Shuah Khan" <shuah@kernel.org>,
	"Jonathan Corbet" <corbet@lwn.net>,
	linux-rdma@vger.kernel.org,
	"Christoph Hellwig" <hch@infradead.org>,
	"Jason Gunthorpe" <jgg@ziepe.ca>,
	"Vlastimil Babka" <vbabka@suse.cz>,
	"Björn Töpel" <bjorn.topel@intel.com>,
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	"David S . Miller" <davem@davemloft.net>,
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Subject: Re: [PATCH 08/19] mm/process_vm_access: set FOLL_PIN via pin_user_pages_remote()
Date: Thu, 31 Oct 2019 16:35:19 -0700	[thread overview]
Message-ID: <20191031233519.GH14771@iweiny-DESK2.sc.intel.com> (raw)
In-Reply-To: <20191030224930.3990755-9-jhubbard@nvidia.com>

On Wed, Oct 30, 2019 at 03:49:19PM -0700, 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().

Ok...  but it made review a bit harder...

Reviewed-by: Ira Weiny <ira.weiny@intel.com>

> 
> Signed-off-by: John Hubbard <jhubbard@nvidia.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
> 