From: Jan Kara <jack@suse.cz>
To: John Hubbard <jhubbard@nvidia.com>
Cc: "Andrew Morton" <akpm@linux-foundation.org>,
"Michael S . Tsirkin" <mst@redhat.com>,
"Jason Wang" <jasowang@redhat.com>,
"Vlastimil Babka" <vbabka@suse.cz>,
"Jérôme Glisse" <jglisse@redhat.com>, "Jan Kara" <jack@suse.cz>,
"Dave Chinner" <david@fromorbit.com>,
"Souptick Joarder" <jrdr.linux@gmail.com>,
"Jonathan Corbet" <corbet@lwn.net>,
linux-doc@vger.kernel.org, linux-fsdevel@vger.kernel.org,
kvm@vger.kernel.org, virtualization@lists.linux-foundation.org,
netdev@vger.kernel.org, LKML <linux-kernel@vger.kernel.org>,
linux-mm@kvack.org
Subject: Re: [PATCH 2/2] vhost: convert get_user_pages() --> pin_user_pages()
Date: Mon, 1 Jun 2020 13:30:00 +0200 [thread overview]
Message-ID: <20200601113000.GE3960@quack2.suse.cz> (raw)
In-Reply-To: <20200529234309.484480-3-jhubbard@nvidia.com>
On Fri 29-05-20 16:43:09, John Hubbard wrote:
> This code was using get_user_pages*(), in approximately a "Case 5"
> scenario (accessing the data within a page), using the categorization
> from [1]. That means that it's time to convert the get_user_pages*() +
> put_page() calls to pin_user_pages*() + unpin_user_pages() calls.
>
> There is some helpful background in [2]: basically, this is a small
> part of fixing a long-standing disconnect between pinning pages, and
> file systems' use of those pages.
>
> [1] Documentation/core-api/pin_user_pages.rst
>
> [2] "Explicit pinning of user-space pages":
> https://lwn.net/Articles/807108/
>
> Cc: Michael S. Tsirkin <mst@redhat.com>
> Cc: Jason Wang <jasowang@redhat.com>
> Cc: kvm@vger.kernel.org
> Cc: virtualization@lists.linux-foundation.org
> Cc: netdev@vger.kernel.org
> Signed-off-by: John Hubbard <jhubbard@nvidia.com>
Looks good to me. You can add:
Reviewed-by: Jan Kara <jack@suse.cz>
Honza
> ---
> drivers/vhost/vhost.c | 5 ++---
> 1 file changed, 2 insertions(+), 3 deletions(-)
>
> diff --git a/drivers/vhost/vhost.c b/drivers/vhost/vhost.c
> index 21a59b598ed8..596132a96cd5 100644
> --- a/drivers/vhost/vhost.c
> +++ b/drivers/vhost/vhost.c
> @@ -1762,15 +1762,14 @@ static int set_bit_to_user(int nr, void __user *addr)
> int bit = nr + (log % PAGE_SIZE) * 8;
> int r;
>
> - r = get_user_pages_fast(log, 1, FOLL_WRITE, &page);
> + r = pin_user_pages_fast(log, 1, FOLL_WRITE, &page);
> if (r < 0)
> return r;
> BUG_ON(r != 1);
> base = kmap_atomic(page);
> set_bit(bit, base);
> kunmap_atomic(base);
> - set_page_dirty_lock(page);
> - put_page(page);
> + unpin_user_pages_dirty_lock(&page, 1, true);
> return 0;
> }
>
> --
> 2.26.2
>
--
Jan Kara <jack@suse.com>
SUSE Labs, CR
next prev parent reply other threads:[~2020-06-01 11:30 UTC|newest]
Thread overview: 9+ messages / expand[flat|nested] mbox.gz Atom feed top
2020-05-29 23:43 [PATCH 0/2] vhost, docs: convert to pin_user_pages(), new "case 5" John Hubbard
2020-05-29 23:43 ` [PATCH 1/2] docs: mm/gup: pin_user_pages.rst: add a " John Hubbard
2020-05-31 7:11 ` Souptick Joarder
2020-06-01 5:11 ` John Hubbard
2020-06-12 19:24 ` Matthew Wilcox
2020-06-12 20:03 ` John Hubbard
2020-05-29 23:43 ` [PATCH 2/2] vhost: convert get_user_pages() --> pin_user_pages() John Hubbard
2020-06-01 11:30 ` Jan Kara [this message]
2020-06-02 4:22 ` Michael S. Tsirkin
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