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

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Message-ID: <5a5133e6-b84d-a2cc-fcb4-db85c4e65d62@oracle.com>
Date:   Mon, 22 Jun 2020 15:10:53 -0400
From:   Boris Ostrovsky <boris.ostrovsky@...cle.com>
To:     Souptick Joarder <jrdr.linux@...il.com>,
        John Hubbard <jhubbard@...dia.com>
Cc:     Juergen Gross <jgross@...e.com>, sstabellini@...nel.org,
        xen-devel@...ts.xenproject.org, linux-kernel@...r.kernel.org,
        paul@....org
Subject: Re: [RFC PATCH] xen/privcmd: Convert get_user_pages*() to
 pin_user_pages*()

On 6/22/20 2:52 PM, Souptick Joarder wrote:
>
> I read the code again. I think, this check is needed to handle a scenario when
> lock_pages() return -ENOSPC. Better to keep this check. Let me post v2 of this
> RFC for a clear view.

Actually, error handling seems to be somewhat broken here. If
lock_pages() returns number of pinned pages then that's what we end up
returning from privcmd_ioctl_dm_op(), all the way to user ioctl(). Which
I don't think is right, we should return proper (negative) error.

Do you mind fixing that we well? Then you should be able to avoid
testing pages in a loop.

-boris