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a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=k20201202; t=1766045131; bh=OzSTS8I7zeGFfn+9aQoFwN8O+cmLb6QBvAXAvMo9Ucs=; h=Date:Subject:To:Cc:References:From:In-Reply-To:From; b=Ly158k2otsUXsxGvg+hMLHK6XdetqPckQe980NBs5BY+zeog2Ysm0rMLTxUR1xmmq Lgyrf96RU2TY79qsWp9dH7QjNC+lyBGTOYaVFGbidHlB0ci74xRtDrO0u43ioFqhVG umLnwu9NFs/nq84gi2yBVjR0ps7YmTwFcXykBRNR/aoFwFr3mdejAucpCJchzNAOOH cpoLvN5RU4E7HrGGT1myxrSe4A++/WmufZPPel1aYw9e1PQAuhyhWfFli3n7hMNXMP KMnhCPxrQsuW7BO1/19blQi8ghAKjBfISLuFefKKWc7R+OoAZGnot2H0pGULjyN9fy IY/gLIGP8D3lg== Message-ID: <6aa47cdb-d2e7-4977-929b-7019b6f991c1@kernel.org> Date: Thu, 18 Dec 2025 09:05:27 +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 , Kevin Brodsky , 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> From: "David Hildenbrand (Red Hat)" Content-Language: en-US In-Reply-To: <37210500-6f6e-46ac-ac2f-ac996308590d@arm.com> Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 7bit X-Rspamd-Queue-Id: 4155810000E X-Rspamd-Server: rspam03 X-Stat-Signature: bz6zda9rypztppsz93siasjxkd3nagfq X-Rspam-User: X-HE-Tag: 1766045132-811575 X-HE-Meta: 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 ZcDDzKmc oM0iVrypKBnxyfZKehlGrdmWxiNlWwbtWPn8ddxkwcRnbaIX2qlLsIcuJ9DR8qurkr8bdxUCTCUttAXYQokRGg41dxr36A6ljYTDuVpn4UG8arCHsZUuvMLqrJWAVVQPWTA6wEBNT/6zTz7v9e3L0cACzdZNJZ6hPTcTwJIExlvTX77RR9o+ynawwJpkDdBI03B+hhkb/s1caSbxjqbPmNPKJpGN65EJqxrIs7ZlDAtL7XlGRHSHLBdW/v1J9h09I8PkrxxTLS6mvPalVVj9MMBYbQMrtdAMRf2W0B3/Yg1yEryzJ3OqSKc0BeZ/lYAKhKjdyL3zm4gtiaOupq0+oQt07J+iyGacpTF8e8TsjrVBNMYQ= 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 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? -- Cheers David