From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from smtp.kernel.org (aws-us-west-2-korg-mail-1.web.codeaurora.org [10.30.226.201]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by smtp.subspace.kernel.org (Postfix) with ESMTPS id BAC14D310; Fri, 26 Jan 2024 07:56:02 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=10.30.226.201 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1706255762; cv=none; b=QPktsrTcgGzi4B/VbLt2/OllIw+OotZ2RjdcwU/63dkpoVMU08gbDzQ7SshAF7pdrmTGKjsu4X52U/77XAu3aDadQovmtmJsqTe9choeSKydMT0CmzCW4enkN7AnMrHkQmEFzsrde/duYzoI5+crMIstItLNFAEOznzQ8ZOvqGE= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1706255762; c=relaxed/simple; bh=3Te0uYkQhoD8wPt8fBPAVzbgCbkYHURjya5IUT8r9v4=; h=Date:To:From:Subject:Message-Id; b=AGN3L3AHQ7I4CigH1Dg1iTHH8YeBG0ZfENU39KToGAGw5q5Uyjt/tHC2Z29vIwNXQyeng5ZUyq0/unh3sSOEvJzeImLAgoJLHfyttzMfdUB3K6QdBGvrw2XY8WBtbFyL/MPUS4Qy4PhevUNrdoXTggKHEJNFRPBShbRE6gslr8M= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dkim=pass (1024-bit key) header.d=linux-foundation.org header.i=@linux-foundation.org header.b=tO5jypqY; arc=none smtp.client-ip=10.30.226.201 Authentication-Results: smtp.subspace.kernel.org; dkim=pass (1024-bit key) header.d=linux-foundation.org header.i=@linux-foundation.org header.b="tO5jypqY" Received: by smtp.kernel.org (Postfix) with ESMTPSA id 14665C433C7; Fri, 26 Jan 2024 07:56:01 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=linux-foundation.org; s=korg; t=1706255762; bh=3Te0uYkQhoD8wPt8fBPAVzbgCbkYHURjya5IUT8r9v4=; h=Date:To:From:Subject:From; b=tO5jypqYDvq/N9ZBgz4fgXZWymeOnWfWIGGmqORvzVhC389TUzdqcvN4FRVLZMJPW E3s+ZdfhtJsw0017IYBiu6oOm0zDJuGy/qSrUM9U9mSxqcQEizOxQ1KKi45XrDyaTy KrOQ+tHvOfWgtEsNO7hfuDPOu7S4HqV5ZNT2BsJI= Date: Thu, 25 Jan 2024 23:55:59 -0800 To: mm-commits@vger.kernel.org,willy@infradead.org,stable@vger.kernel.org,riel@surriel.com,muchun.song@linux.dev,lstoakes@gmail.com,leitao@debian.org,akpm@linux-foundation.org From: Andrew Morton Subject: [merged mm-stable] mm-hugetlb-restore-the-reservation-if-needed.patch removed from -mm tree Message-Id: <20240126075602.14665C433C7@smtp.kernel.org> Precedence: bulk X-Mailing-List: mm-commits@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: The quilt patch titled Subject: mm/hugetlb: restore the reservation if needed has been removed from the -mm tree. Its filename was mm-hugetlb-restore-the-reservation-if-needed.patch This patch was dropped because it was merged into the mm-stable branch of git://git.kernel.org/pub/scm/linux/kernel/git/akpm/mm ------------------------------------------------------ From: Breno Leitao Subject: mm/hugetlb: restore the reservation if needed Date: Wed, 17 Jan 2024 09:10:57 -0800 Currently there is a bug that a huge page could be stolen, and when the original owner tries to fault in it, it causes a page fault. You can achieve that by: 1) Creating a single page echo 1 > /sys/kernel/mm/hugepages/hugepages-2048kB/nr_hugepages 2) mmap() the page above with MAP_HUGETLB into (void *ptr1). * This will mark the page as reserved 3) touch the page, which causes a page fault and allocates the page * This will move the page out of the free list. * It will also unreserved the page, since there is no more free page 4) madvise(MADV_DONTNEED) the page * This will free the page, but not mark it as reserved. 5) Allocate a secondary page with mmap(MAP_HUGETLB) into (void *ptr2). * it should fail, but, since there is no more available page. * But, since the page above is not reserved, this mmap() succeed. 6) Faulting at ptr1 will cause a SIGBUS * it will try to allocate a huge page, but there is none available A full reproducer is in selftest. See https://lore.kernel.org/all/20240105155419.1939484-1-leitao@debian.org/ Fix this by restoring the reserved page if necessary. If the page being unmapped has HPAGE_RESV_OWNER set, and needs a reservation, set the restore_reserve flag, which will move the page from free to reserved. Link: https://lkml.kernel.org/r/20240117171058.2192286-1-leitao@debian.org Signed-off-by: Breno Leitao Suggested-by: Rik van Riel Cc: Lorenzo Stoakes Cc: Matthew Wilcox (Oracle) Cc: Muchun Song Cc: Rik van Riel Cc: Signed-off-by: Andrew Morton --- mm/hugetlb.c | 10 ++++++++++ 1 file changed, 10 insertions(+) --- a/mm/hugetlb.c~mm-hugetlb-restore-the-reservation-if-needed +++ a/mm/hugetlb.c @@ -5677,6 +5677,16 @@ void __unmap_hugepage_range(struct mmu_g hugetlb_count_sub(pages_per_huge_page(h), mm); hugetlb_remove_rmap(page_folio(page)); + if (is_vma_resv_set(vma, HPAGE_RESV_OWNER) && + vma_needs_reservation(h, vma, start)) { + /* + * Restore the reservation if needed, otherwise the + * backing page could be stolen by someone. + */ + folio_set_hugetlb_restore_reserve(page_folio(page)); + vma_add_reservation(h, vma, address); + } + spin_unlock(ptl); tlb_remove_page_size(tlb, page, huge_page_size(h)); /* _ Patches currently in -mm which might be from leitao@debian.org are selftests-mm-new-test-that-steals-pages.patch