linux-kernel - RE: [PATCH v3 1/3] xen/privcmd: Corrected error handling path

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Date:   Mon, 13 Jul 2020 09:08:04 +0100
From:   Paul Durrant <xadimgnik@...il.com>
To:     "'Souptick Joarder'" <jrdr.linux@...il.com>,
        <boris.ostrovsky@...cle.com>, <jgross@...e.com>,
        <sstabellini@...nel.org>
Cc:     <xen-devel@...ts.xenproject.org>, <linux-kernel@...r.kernel.org>,
        "'John Hubbard'" <jhubbard@...dia.com>,
        "'Paul Durrant'" <xadimgnik@...il.com>
Subject: RE: [PATCH v3 1/3] xen/privcmd: Corrected error handling path

> -----Original Message-----
> From: Souptick Joarder <jrdr.linux@...il.com>
> Sent: 12 July 2020 04:40
> To: boris.ostrovsky@...cle.com; jgross@...e.com; sstabellini@...nel.org
> Cc: xen-devel@...ts.xenproject.org; linux-kernel@...r.kernel.org; Souptick Joarder
> <jrdr.linux@...il.com>; John Hubbard <jhubbard@...dia.com>; Paul Durrant <xadimgnik@...il.com>
> Subject: [PATCH v3 1/3] xen/privcmd: Corrected error handling path
> 
> Previously, if lock_pages() end up partially mapping pages, it used
> to return -ERRNO due to which unlock_pages() have to go through
> each pages[i] till *nr_pages* to validate them. This can be avoided
> by passing correct number of partially mapped pages & -ERRNO separately,
> while returning from lock_pages() due to error.
> 
> With this fix unlock_pages() doesn't need to validate pages[i] till
> *nr_pages* for error scenario and few condition checks can be ignored.
> 
> Signed-off-by: Souptick Joarder <jrdr.linux@...il.com>
> Reviewed-by: Juergen Gross <jgross@...e.com>
> Cc: John Hubbard <jhubbard@...dia.com>
> Cc: Boris Ostrovsky <boris.ostrovsky@...cle.com>
> Cc: Paul Durrant <xadimgnik@...il.com>

Reviewed-by: Paul Durrant <paul@....org>

> ---
>  drivers/xen/privcmd.c | 31 +++++++++++++++----------------
>  1 file changed, 15 insertions(+), 16 deletions(-)
> 
> diff --git a/drivers/xen/privcmd.c b/drivers/xen/privcmd.c
> index 5dfc59f..b001673 100644
> --- a/drivers/xen/privcmd.c
> +++ b/drivers/xen/privcmd.c
> @@ -579,13 +579,13 @@ static long privcmd_ioctl_mmap_batch(
> 
>  static int lock_pages(
>  	struct privcmd_dm_op_buf kbufs[], unsigned int num,
> -	struct page *pages[], unsigned int nr_pages)
> +	struct page *pages[], unsigned int nr_pages, unsigned int *pinned)
>  {
>  	unsigned int i;
> 
>  	for (i = 0; i < num; i++) {
>  		unsigned int requested;
> -		int pinned;
> +		int page_count;
> 
>  		requested = DIV_ROUND_UP(
>  			offset_in_page(kbufs[i].uptr) + kbufs[i].size,
> @@ -593,14 +593,15 @@ static int lock_pages(
>  		if (requested > nr_pages)
>  			return -ENOSPC;
> 
> -		pinned = get_user_pages_fast(
> +		page_count = get_user_pages_fast(
>  			(unsigned long) kbufs[i].uptr,
>  			requested, FOLL_WRITE, pages);
> -		if (pinned < 0)
> -			return pinned;
> +		if (page_count < 0)
> +			return page_count;
> 
> -		nr_pages -= pinned;
> -		pages += pinned;
> +		*pinned += page_count;
> +		nr_pages -= page_count;
> +		pages += page_count;
>  	}
> 
>  	return 0;
> @@ -610,13 +611,8 @@ static void unlock_pages(struct page *pages[], unsigned int nr_pages)
>  {
>  	unsigned int i;
> 
> -	if (!pages)
> -		return;
> -
> -	for (i = 0; i < nr_pages; i++) {
> -		if (pages[i])
> -			put_page(pages[i]);
> -	}
> +	for (i = 0; i < nr_pages; i++)
> +		put_page(pages[i]);
>  }
> 
>  static long privcmd_ioctl_dm_op(struct file *file, void __user *udata)
> @@ -629,6 +625,7 @@ static long privcmd_ioctl_dm_op(struct file *file, void __user *udata)
>  	struct xen_dm_op_buf *xbufs = NULL;
>  	unsigned int i;
>  	long rc;
> +	unsigned int pinned = 0;
> 
>  	if (copy_from_user(&kdata, udata, sizeof(kdata)))
>  		return -EFAULT;
> @@ -682,9 +679,11 @@ static long privcmd_ioctl_dm_op(struct file *file, void __user *udata)
>  		goto out;
>  	}
> 
> -	rc = lock_pages(kbufs, kdata.num, pages, nr_pages);
> -	if (rc)
> +	rc = lock_pages(kbufs, kdata.num, pages, nr_pages, &pinned);
> +	if (rc < 0) {
> +		nr_pages = pinned;
>  		goto out;
> +	}
> 
>  	for (i = 0; i < kdata.num; i++) {
>  		set_xen_guest_handle(xbufs[i].h, kbufs[i].uptr);
> --
> 1.9.1