From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from smtp.kernel.org (aws-us-west-2-korg-mail-alma10-1.taild15c8.ts.net [100.103.45.18]) (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 B51135012A2 for ; Mon, 21 Sep 2026 19:00:00 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=100.103.45.18 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1790017202; cv=none; b=JedTV3PhfuJ9GQf8LpwytznekhEbmTNh12xQUUglSRVvoBFpp9ZrojlxgQtme4GgF4C3MrYcYtPTHsia5rGUrb8jJgVYBGztOWgmjTaytZJDUAuOA4FiBEPbtQxmULrdJOaxlJaOcDfVTwLd6JFJDBw/QgTLeEJhtXmUiRxU3SM= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1790017202; c=relaxed/simple; bh=/ZkqrmpM4CxMXRQHWMajSNcKQyTTrfktt6Hn4TwwVsw=; h=Message-ID:Date:MIME-Version:Subject:To:Cc:References:From: In-Reply-To:Content-Type; b=REP+u19Tw9GJkgRWiPJFC5Kr8Rj8M2asqvirindjmCCGmzf4491abvL0bussNIXwFjQozR9W9ExUrC0olHGrXAJ5XMtaoi4D7yN3NVf7IN/U0K/JfqpOjZbqgsOWKgfmA1uBkIQIb30qeEcum7antqp3CS22we/OLG7RT0lRdr8= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b=akEmkLS7; arc=none smtp.client-ip=100.103.45.18 Authentication-Results: smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b="akEmkLS7" Received: by smtp.kernel.org (Postfix) with ESMTPSA id 022971F000FF; Mon, 21 Sep 2026 18:59:54 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=kernel.org; s=k20260515; t=1790017200; bh=BowEjN3QHu7cKrFM2s4WvhKI/ELZmnQl4hyHemGhzeI=; h=Date:Subject:To:Cc:References:From:In-Reply-To; b=akEmkLS7ZDQTu8lus8F9aGBXvZ+PK9spg1Au2o6EZRbCw2Hw9awxVv2IXe4he/g6H O0WpKNKWzEzJtVnVJK1PDdyTE5P61zauMxJfsTJvY3TUgYj+trQhakmg4bH11KFZnu FEICOjEawjwjjNk/khAhUy6+LffID6T30hh5ePDNQkbnV2LGRpbf8h2YzYDybssBBz w1jUbXibQ+pkh6m6yhH5JT++qvuHb/fxKe6Dtek/VEB+ij0Mj1/dPLSbRNLURc7MPg ZMxBOsKKOsCdx/Go6/W49CkMljZ5xb1jm6aIqhjAb2dzC9mhfjU1d8Oqe8oC2Kuev6 svSPcC3Q5p+mg== Message-ID: <4de1dfb3-b349-4916-9fe0-6b9697583ac7@kernel.org> Date: Mon, 21 Sep 2026 20:59:50 +0200 Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH v3 2/2] mm: selftests: Adjust the MADV_COLLAPSE uffd-minor selftests To: James Houghton , Andrew Morton Cc: Lorenzo Stoakes , Zi Yan , Baolin Wang , liam@infradead.org, Nico Pache , Ryan Roberts , Dev Jain , Barry Song , Lance Yang , Usama Arif , Yang Shi , zokeefe@google.com, hughd@google.com, Kiryl Shutsemau , linux-mm@kvack.org, linux-kernel@vger.kernel.org References: <20260910023411.514987-1-jthoughton@google.com> <20260910023411.514987-2-jthoughton@google.com> From: "David Hildenbrand (Arm)" Content-Language: en-US Autocrypt: addr=david@kernel.org; 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charset=UTF-8 Content-Transfer-Encoding: 7bit On 9/10/26 04:34, James Houghton wrote: > The behavior of MADV_COLLAPSE with uffd-minor VMAs has changed: > MADV_COLLAPSE will no longer install PTEs where none existed before. Misleading: MADV_COLLAPSE installed a PMD not PTEs? > Update the selftest to demonstrate this new behavior. > > On an unpatched kernel, the test will hit "unexpected memory contents > after collapse". > > If the selftest is left unpatched but the kernel is patched, the > selftest will SKIP when it gets EINVAL back from MADV_COLLAPSE. > > Signed-off-by: James Houghton > --- > tools/testing/selftests/mm/uffd-unit-tests.c | 75 ++++++++++++++++++-- > 1 file changed, 68 insertions(+), 7 deletions(-) > > diff --git a/tools/testing/selftests/mm/uffd-unit-tests.c b/tools/testing/selftests/mm/uffd-unit-tests.c > index ef9b3956bdcf..6f2360f9b75d 100644 > --- a/tools/testing/selftests/mm/uffd-unit-tests.c > +++ b/tools/testing/selftests/mm/uffd-unit-tests.c > @@ -518,19 +518,34 @@ static void uffd_wp_fork_pin_with_event_test(uffd_global_test_opts_t *gopts, uff > uffd_wp_fork_pin_test_common(gopts, args, true); > } > > -static void check_memory_contents(uffd_global_test_opts_t *gopts, char *p) > +static int __check_memory_contents(unsigned long offset, > + unsigned long nr_pages, > + uffd_global_test_opts_t *gopts, > + char *p) Two tabs look better ;) > { > unsigned long i, j; > uint8_t expected_byte; > > - for (i = 0; i < gopts->nr_pages; ++i) { > + if (nr_pages + offset < nr_pages) > + err("overflow in memory check"); > + if (nr_pages + offset > gopts->nr_pages) > + err("out of bounds memory check"); > + > + for (i = offset; i < offset + nr_pages; ++i) { > expected_byte = ~((uint8_t)(i % ((uint8_t)-1))); > for (j = 0; j < gopts->page_size; j++) { > uint8_t v = *(uint8_t *)(p + (i * gopts->page_size) + j); > if (v != expected_byte) > - err("unexpected page contents"); > + return 1; > } > } > + > + return 0; > +} > + > +static int check_memory_contents(uffd_global_test_opts_t *gopts, char *p) > +{ > + return __check_memory_contents(0, gopts->nr_pages, gopts, p); > } > > static void uffd_minor_test_common(uffd_global_test_opts_t *gopts, bool test_collapse, bool test_wp) > @@ -539,6 +554,8 @@ static void uffd_minor_test_common(uffd_global_test_opts_t *gopts, bool test_col > pthread_t uffd_mon; > char c = '\0'; > struct uffd_args args = { 0 }; > + unsigned long checked = 0; > + bool bad_contents; Through in an empty line. Or better struct uffd_args args = { .gopts = gopts }; > > /* > @@ -564,24 +581,65 @@ static void uffd_minor_test_common(uffd_global_test_opts_t *gopts, bool test_col > if (pthread_create(&uffd_mon, NULL, uffd_poll_thread, &args)) > err("uffd_poll_thread create"); > > + if (test_collapse) { > + /* > + * Read just a single page and try collapsing. The collapse > + * should either be rejected or be a no-op. > + */ > + if (__check_memory_contents(0, 1, gopts, gopts->area_dst_alias)) > + err("unexpected memory contents before collapse"); > + > + /* MADV_COLLAPSE might return EINVAL for uffd-minor VMAs. */ > + madvise(gopts->area_dst_alias, gopts->nr_pages * gopts->page_size, > + MADV_COLLAPSE); Add an explicit check for expected errnos? > + /* > + * If the above collapse mapped pages that were not explicitly > + * CONTINUE'd, the below __check_memory_contents() will not > + * fault on some pages, resulting in incorrect contents. The > + * PTE for the first page may get retracted, so avoid checking > + * that page, as we might take a second fault, flipping the > + * contents a second time. > + */ > + checked = 1; I'm not an expert on this code. But a trivial check to see whether there is something in the page tables that shouldn't be there is through the help of pagemap_is_populated(). Maybe that would help to simplify things, not sure. -- Cheers, David