From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from foss.arm.com (foss.arm.com [217.140.110.172]) by smtp.subspace.kernel.org (Postfix) with ESMTP id 186912F3621; Thu, 18 Dec 2025 13:18:41 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=217.140.110.172 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1766063924; cv=none; b=irhP14HH1F/bkb/i1D604nKrL4ZOVPpGKy5EnVmh4qvXWZ6IpsXEbHb0dN/fzyHQ9G0C7eUnWfnktnq41bNJeST0bU5CWc2pI0IbBkXKcGCBD2k6/vPCGj3reqyQmw9v7PQQdEpZVqET8uC+BNo88qLe0Wwrau4qKHGwq9TVKbg= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1766063924; c=relaxed/simple; bh=OnSYbaFp2CAHTZ+yw/lF5QDuvZiXHxAuex7bg8JKT8Y=; h=Message-ID:Date:MIME-Version:Subject:To:Cc:References:From: In-Reply-To:Content-Type; b=Cp85iNPFe3mEvnExSg/XuAWEJkUZxxcy9cUI7k3HeLg76jAg+XuX1UW0AT807dgFF8lKJQGk5E5hqaezVWPxHIK1VayiCbKA3eqHsCI8PojxkO8CNyp35Mk97DM2UOAsJz3RDB7EqfBY2Rld7QgWNIgYW8jFbvKu3UM2MztKKzU= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dmarc=pass (p=none dis=none) header.from=arm.com; spf=pass smtp.mailfrom=arm.com; arc=none smtp.client-ip=217.140.110.172 Authentication-Results: smtp.subspace.kernel.org; dmarc=pass (p=none dis=none) header.from=arm.com Authentication-Results: smtp.subspace.kernel.org; spf=pass smtp.mailfrom=arm.com Received: from usa-sjc-imap-foss1.foss.arm.com (unknown [10.121.207.14]) by usa-sjc-mx-foss1.foss.arm.com (Postfix) with ESMTP id EC3F0FEC; Thu, 18 Dec 2025 05:18:33 -0800 (PST) Received: from [10.57.45.71] (unknown [10.57.45.71]) by usa-sjc-imap-foss1.foss.arm.com (Postfix) with ESMTPSA id C2C763F73F; Thu, 18 Dec 2025 05:18:38 -0800 (PST) Message-ID: <0575bcf6-c1a3-4ebf-a199-3113758fbdc5@arm.com> Date: Thu, 18 Dec 2025 14:18:35 +0100 Precedence: bulk X-Mailing-List: linux-kselftest@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH 3/4] selftests/mm: fix faulting-in code in pagemap_ioctl test To: "David Hildenbrand (Red Hat)" , Ryan Roberts , linux-mm@kvack.org, linux-kselftest@vger.kernel.org Cc: linux-kernel@vger.kernel.org, Andrew Morton , Lorenzo Stoakes , Mark Brown , Shuah Khan , Usama Anjum References: <20251216142633.2401447-1-kevin.brodsky@arm.com> <20251216142633.2401447-4-kevin.brodsky@arm.com> <37210500-6f6e-46ac-ac2f-ac996308590d@arm.com> <6aa47cdb-d2e7-4977-929b-7019b6f991c1@kernel.org> From: Kevin Brodsky Content-Language: en-GB In-Reply-To: <6aa47cdb-d2e7-4977-929b-7019b6f991c1@kernel.org> Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 8bit On 18/12/2025 09:05, David Hildenbrand (Red Hat) wrote: > On 12/16/25 15:56, Ryan Roberts wrote: >> On 16/12/2025 14:26, Kevin Brodsky wrote: >>> One of the pagemap_ioctl tests attempts to fault in pages by >>> memcpy()'ing them to an unused buffer. This probably worked >>> originally, but since commit 46036188ea1f ("selftests/mm: build with >>> -O2") the compiler is free to optimise away that unused buffer and >>> the memcpy() with it. As a result there might not be any resident >>> page in the mapping and the test may fail. >>> >>> We don't need to copy all that memory anyway. Just fault in every >>> page by forcing the compiler to read the first byte. >>> >>> Cc: Usama Anjum >>> Signed-off-by: Kevin Brodsky >>> --- >>>   tools/testing/selftests/mm/pagemap_ioctl.c | 6 +++--- >>>   1 file changed, 3 insertions(+), 3 deletions(-) >>> >>> diff --git a/tools/testing/selftests/mm/pagemap_ioctl.c >>> b/tools/testing/selftests/mm/pagemap_ioctl.c >>> index 2cb5441f29c7..67a7a3705604 100644 >>> --- a/tools/testing/selftests/mm/pagemap_ioctl.c >>> +++ b/tools/testing/selftests/mm/pagemap_ioctl.c >>> @@ -1056,7 +1056,6 @@ int sanity_tests(void) >>>       struct page_region *vec; >>>       char *mem, *fmem; >>>       struct stat sbuf; >>> -    char *tmp_buf; >>>         /* 1. wrong operation */ >>>       mem_size = 10 * page_size; >>> @@ -1167,8 +1166,9 @@ int sanity_tests(void) >>>       if (fmem == MAP_FAILED) >>>           ksft_exit_fail_msg("error nomem %d %s\n", errno, >>> strerror(errno)); >>>   -    tmp_buf = malloc(sbuf.st_size); >>> -    memcpy(tmp_buf, fmem, sbuf.st_size); >>> +    /* Fault in every page by reading the first byte */ >>> +    for (i = 0; i < sbuf.st_size; i += page_size) >>> +        (void)*(volatile char *)(fmem + i); >> >> We have FORCE_READ() in vm_util.h for this. Perhaps that would be >> better? > > Agreed, and if we have multiple patterns where we want to force_read a > bigger area, maybe we should provide a helper for that? I've found just a couple of cases where FORCE_READ() is used for a larger area (in hugetlb-madvise.c and split_huge_page_test.c). The step size isn't the same in any of these cases though. We could have something like fault_area(addr, size, step) but maybe the loops are clear enough already? - Kevin