linux-kernel - RE: [RFC PATCH] block, fs: use FOLL_LONGTERM as gup

lists.openwall.net		lists / announce owl-users owl-dev john-users john-dev passwdqc-users yescrypt popa3d-users / oss-security kernel-hardening musl sabotage tlsify passwords / crypt-dev xvendor / Bugtraq Full-Disclosure linux-kernel linux-netdev linux-ext4 linux-hardening linux-cve-announce PHC
Open Source and information security mailing list archives

Hash Suite: Windows password security audit tool. GUI, reports in PDF.

[<prev] [next>] [<thread-prev] [thread-next>] [day] [month] [year] [list]

Message-ID: <848301db8f05$a1d79430$e586bc90$@samsung.com>
Date: Fri, 7 Mar 2025 11:07:08 +0900
From: "Sooyong Suk" <s.suk@...sung.com>
To: "'Jaewon Kim'" <jaewon31.kim@...il.com>, "'Christoph Hellwig'"
	<hch@...radead.org>
Cc: <viro@...iv.linux.org.uk>, <linux-kernel@...r.kernel.org>,
	<akpm@...ux-foundation.org>, <linux-mm@...ck.org>, <spssyr@...il.com>,
	<axboe@...nel.dk>, <linux-block@...r.kernel.org>, <dhavale@...gle.com>,
	<surenb@...gle.com>
Subject: RE: [RFC PATCH] block, fs: use FOLL_LONGTERM as gup_flags for
 direct IO

> On Fri, Mar 7, 2025 at 12:26 AM Christoph Hellwig <hch@...radead.org>
> wrote:
> >
> > On Thu, Mar 06, 2025 at 04:40:56PM +0900, Sooyong Suk wrote:
> > > There are GUP references to pages that are serving as direct IO
> buffers.
> > > Those pages can be allocated from CMA pageblocks despite they can be
> > > pinned until the DIO is completed.
> >
> > direct I/O is eactly the case that is not FOLL_LONGTERM and one of the
> > reasons to even have the flag.  So big fat no to this.
> >
> 

Understood.

> Hello, thank you for your comment.
> We, Sooyong and I, wanted to get some opinions about this FOLL_LONGTERM
> for direct I/O as CMA memory got pinned pages which had been pinned from
> direct io.
> 
> > You also completely failed to address the relevant mailinglist and
> > maintainers.
> 
> I added block maintainer Jens Axboe and the block layer maillinst here,
> and added Suren and Sandeep, too.

Then, what do you think of using PF_MEMALLOC_PIN for this context as below?
This will only remove __GFP_MOVABLE from its allocation flag.
Since __bio_iov_iter_get_pages() indicates that it will pin user or kernel pages,
there seems to be no reason not to use this process flag.

block/bio.c | 3 +++
 1 file changed, 3 insertions(+)

diff --git a/block/bio.c b/block/bio.c
index 65c796ecb..671e28966 100644
--- a/block/bio.c
+++ b/block/bio.c
@@ -1248,6 +1248,7 @@ static int __bio_iov_iter_get_pages(struct bio *bio, struct iov_iter *iter)
 	unsigned len, i = 0;
 	size_t offset;
 	int ret = 0;
+	unsigned int flags;
 
 	/*
 	 * Move page array up in the allocated memory for the bio vecs as far as
@@ -1267,9 +1268,11 @@ static int __bio_iov_iter_get_pages(struct bio *bio, struct iov_iter *iter)
 	 * result to ensure the bio's total size is correct. The remainder of
 	 * the iov data will be picked up in the next bio iteration.
 	 */
+	flags = memalloc_pin_save();
 	size = iov_iter_extract_pages(iter, &pages,
 				      UINT_MAX - bio->bi_iter.bi_size,
 				      nr_pages, extraction_flags, &offset);
+	memalloc_pin_restore(flags);
 	if (unlikely(size <= 0))
 		return size ? size : -EFAULT;