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Date: Thu, 7 Jan 2021 12:32:09 -0800 From: Linus Torvalds <torvalds@...ux-foundation.org> To: Jason Gunthorpe <jgg@...pe.ca> Cc: Andrea Arcangeli <aarcange@...hat.com>, Linux-MM <linux-mm@...ck.org>, Linux Kernel Mailing List <linux-kernel@...r.kernel.org>, Yu Zhao <yuzhao@...gle.com>, Andy Lutomirski <luto@...nel.org>, Peter Xu <peterx@...hat.com>, Pavel Emelyanov <xemul@...nvz.org>, Mike Kravetz <mike.kravetz@...cle.com>, Mike Rapoport <rppt@...ux.vnet.ibm.com>, Minchan Kim <minchan@...nel.org>, Will Deacon <will@...nel.org>, Peter Zijlstra <peterz@...radead.org>, Hugh Dickins <hughd@...gle.com>, "Kirill A. Shutemov" <kirill.shutemov@...ux.intel.com>, Matthew Wilcox <willy@...radead.org>, Oleg Nesterov <oleg@...hat.com>, Jann Horn <jannh@...gle.com>, Kees Cook <keescook@...omium.org>, John Hubbard <jhubbard@...dia.com>, Leon Romanovsky <leonro@...dia.com>, Jan Kara <jack@...e.cz>, Kirill Tkhai <ktkhai@...tuozzo.com> Subject: Re: [PATCH 0/2] page_count can't be used to decide when wp_page_copy On Thu, Jan 7, 2021 at 12:25 PM Jason Gunthorpe <jgg@...pe.ca> wrote: > > Lots of places are relying on pin_user_pages long term pins of memory, > and cannot be converted to notifiers. > > I don't think it is reasonable to just declare that insecure and > requires privileges, it is a huge ABI break. Also, I think GUP (and pin_user_pages() as a special case) is a lot more important and more commonly used than UFFD. Which is really why I think this needs to be fixed by just fixing UFFD to take the write lock. I think Andrea is blinded by his own love for UFFDIO: when I do a debian codesearch for UFFDIO_WRITEPROTECT, all it finds is the kernel and strace (and the qemu copies of the kernel headers). Does the debian code search cover everything? Obviously not. But if you cannot find A SINGLE USE of that thing in the Debian code search, then that is sure a sign of _something_. Linus
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