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imf25.hostedemail.com; dkim=none; dmarc=pass (policy=none) header.from=arm.com; spf=pass (imf25.hostedemail.com: domain of kevin.brodsky@arm.com designates 217.140.110.172 as permitted sender) smtp.mailfrom=kevin.brodsky@arm.com ARC-Seal: i=1; s=arc-20220608; d=hostedemail.com; t=1765897924; a=rsa-sha256; cv=none; b=cnONInKN5irIbFogZ1iWr9G9FGjp/ue7CEN8PTqJMMVd4KkM0wmGQ0EtllsLH8xys24rhE Mybxc0OkC20NTSMSmb2+LVhxGFC8YKrN5X7MWS8jxhft4QO4Zld5o5tEXKJQL6pCEfll0r /ILqJFZSqSjKQwoQfJMMSIZoZYtJuzM= 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 7F93D1516; Tue, 16 Dec 2025 07:11:56 -0800 (PST) Received: from [10.44.160.64] (e126510-lin.lund.arm.com [10.44.160.64]) by usa-sjc-imap-foss1.foss.arm.com (Postfix) with ESMTPSA id A6DDC3F73B; Tue, 16 Dec 2025 07:12:01 -0800 (PST) Message-ID: Date: Tue, 16 Dec 2025 16:11:58 +0100 MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH 3/4] selftests/mm: fix faulting-in code in pagemap_ioctl test To: Ryan Roberts , linux-mm@kvack.org, linux-kselftest@vger.kernel.org Cc: linux-kernel@vger.kernel.org, Andrew Morton , David Hildenbrand , 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> From: Kevin Brodsky Content-Language: en-GB In-Reply-To: <37210500-6f6e-46ac-ac2f-ac996308590d@arm.com> Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 7bit X-Rspam-User: X-Rspamd-Server: rspam11 X-Rspamd-Queue-Id: 6286AA0015 X-Stat-Signature: itdgjjwq9pse5zmsypwi7zzrmjwqewop X-HE-Tag: 1765897924-508383 X-HE-Meta: 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 YxpEgsr8 +4PhKIs7n22/a36ikt1tQl+2k1x0mXqBI1emMX/ophLstiNjsvmOJ2Dt3iBNFESN8m7dH0AGkyPrftFDGD8cNzQgBodOvSr2gIdUiFnAhiD6mF1RmSF05nbyvOsQf1HYu6ttntFAoWezuELWTumT0j0GYgI87j4qwAAw1ObK5WSYknGyxzJTugun0kWCDd+LnAwlnLqwrqztTG8/tffWjAW9KZKhJUyvP5EBxIG9N2q+BtqbchWWfA/CT/w== X-Bogosity: Ham, tests=bogofilter, spamicity=0.000000, version=1.2.4 Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: List-Subscribe: List-Unsubscribe: On 16/12/2025 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? It would, thanks! I wanted to use READ_ONCE() from tools/include/linux/compiler.h but for some reason we don't add tools/include to the include path in the mm kselftests Makefile and I didn't want to dive into that rabbit hole. - Kevin