linux-kernel - Re: [PATCH] mm/gup: restore the ability to pin more than 2GB at a time

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Message-ID: <ZyG0VKUpFttPF30f@infradead.org>
Date: Tue, 29 Oct 2024 21:21:40 -0700
From: Christoph Hellwig <hch@...radead.org>
To: John Hubbard <jhubbard@...dia.com>
Cc: Andrew Morton <akpm@...ux-foundation.org>,
	LKML <linux-kernel@...r.kernel.org>, linux-mm@...ck.org,
	linux-stable@...r.kernel.org,
	Vivek Kasireddy <vivek.kasireddy@...el.com>,
	David Hildenbrand <david@...hat.com>,
	Dave Airlie <airlied@...hat.com>, Gerd Hoffmann <kraxel@...hat.com>,
	Matthew Wilcox <willy@...radead.org>,
	Christoph Hellwig <hch@...radead.org>,
	Jason Gunthorpe <jgg@...dia.com>, Peter Xu <peterx@...hat.com>,
	Arnd Bergmann <arnd@...db.de>,
	Daniel Vetter <daniel.vetter@...ll.ch>,
	Dongwon Kim <dongwon.kim@...el.com>,
	Hugh Dickins <hughd@...gle.com>,
	Junxiao Chang <junxiao.chang@...el.com>,
	Mike Kravetz <mike.kravetz@...cle.com>,
	Oscar Salvador <osalvador@...e.de>
Subject: Re: [PATCH] mm/gup: restore the ability to pin more than 2GB at a
 time

On Tue, Oct 29, 2024 at 08:01:16PM -0700, John Hubbard wrote:
> A user-visible consequence has now appeared: user space can no longer
> pin more than 2GB of memory anymore on x86_64. That's because, on a 4KB
> PAGE_SIZE system, when user space tries to (indirectly, via a device
> driver that calls pin_user_pages()) pin 2GB, this requires an allocation
> of a folio pointers array of MAX_PAGE_ORDER size, which is the limit for
> kmalloc().

Do you have a report whee someone tries to pin that much memor in a
single call?  What driver is this?  Because it seems like a not very
smart thing to do.