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Thu, 2 Apr 2026 07:31:21 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=k20201202; t=1775115086; bh=LB/+oqKlI4VRU5D1rjvBo04nLr5ECYtn29znNNozBBs=; h=Date:Subject:To:Cc:References:From:In-Reply-To:From; b=tMPIrBvKTo40byCvRHv/28b+KqoC03TZRGKKrgRpkMzvXCSuJUdMY/EoIx48skJE1 pAkwb80w8EdBKR3zTVIxlc4RdsMGGm2DgW/R+Me9bVea1VDevoQHRqZOcdF/XGR7Pf i/KHLYGmyG9qPEVVvgFkKWzdYXCXIP5Jzw+IxQ2PCrsAlDc27p0EAWkb/bPvMB+oyj ny5NhcJ8nexHxMXECxD0WVtcyHBRSIx61acnotLrQcc5fFiedg95GQOcVvdq9M3bBE Lszm77bdUctMVWYUQx3IK7mZYZDY757Tv5MuRoh5MrT/0+Z2a9S4zLaqfIq6KT/yfP J8rwI4BZG+lXA== Message-ID: Date: Thu, 2 Apr 2026 09:31:18 +0200 X-Mailing-List: linuxppc-dev@lists.ozlabs.org List-Id: List-Help: List-Owner: List-Post: List-Archive: , List-Subscribe: , , List-Unsubscribe: Precedence: list MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH v3 07/13] selftest/mm: register existing mapping with userfaultfd in hugepage-mremap To: Sayali Patil , Andrew Morton , Shuah Khan , linux-mm@kvack.org, linux-kernel@vger.kernel.org, linux-kselftest@vger.kernel.org, Ritesh Harjani Cc: Zi Yan , Michal Hocko , Oscar Salvador , Lorenzo Stoakes , Dev Jain , Liam.Howlett@oracle.com, linuxppc-dev@lists.ozlabs.org, Venkat Rao Bagalkote References: <142f8c68-43c7-4a6a-bd2c-1c5ebda09b27@kernel.org> <7b6652f3-c994-4ef4-87a4-5473cd1254b7@linux.ibm.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 4/1/26 16:43, Sayali Patil wrote: > > On 01/04/26 19:48, David Hildenbrand (Arm) wrote: >> On 3/27/26 08:16, Sayali Patil wrote: >>> Previously, register_region_with_uffd() created a new anonymous >>> mapping and overwrote the address supplied by the caller before >>> registering the range with userfaultfd. >>> >>> As a result, userfaultfd was applied to an unrelated anonymous mapping >>> instead of the hugetlb region used by the test. >>> >>> Remove the extra mmap() and register the caller-provided address range >>> directly using UFFDIO_REGISTER_MODE_MISSING, so that faults are >>> generated for the hugetlb mapping used by the test. >>> >>> This ensures userfaultfd operates on the actual hugetlb test region and >>> validates the expected fault handling. >>> >>> Before patch: >>> running ./hugepage-mremap >>> ------------------------- >>> TAP version 13 >>> 1..1 >>> Map haddr: Returned address is 0x7eaa40000000 >>> Map daddr: Returned address is 0x7daa40000000 >>> Map vaddr: Returned address is 0x7faa40000000 >>> Address returned by mmap() = 0x7fff9d000000 >>> Mremap: Returned address is 0x7faa40000000 >>> First hex is 0 >>> First hex is 3020100 >>> ok 1 Read same data >>> Totals: pass:1 fail:0 xfail:0 xpass:0 skip:0 error:0 >>> [PASS] >>> ok 1 hugepage-mremap >>> >>> After patch: >>> running ./hugepage-mremap >>> ------------------------- >>> TAP version 13 >>> 1..1 >>> Map haddr: Returned address is 0x7eaa40000000 >>> Map daddr: Returned address is 0x7daa40000000 >>> Map vaddr: Returned address is 0x7faa40000000 >>> Registered memory at address 0x7eaa40000000 with userfaultfd >>> Mremap: Returned address is 0x7faa40000000 >>> First hex is 0 >>> First hex is 3020100 >>> ok 1 Read same data >>> Totals: pass:1 fail:0 xfail:0 xpass:0 skip:0 error:0 >>> [PASS] >>> ok 1 hugepage-mremap >> Okay, so we tested mremap() of something that is not even hugetlb. >> >>> Fixes: 12b613206474 ("mm, hugepages: add hugetlb vma mremap() test") >>> Tested-by: Venkat Rao Bagalkote >>> Signed-off-by: Sayali Patil >>> --- >>> tools/testing/selftests/mm/hugepage-mremap.c | 21 +++++--------------- >>> 1 file changed, 5 insertions(+), 16 deletions(-) >>> >>> diff --git a/tools/testing/selftests/mm/hugepage-mremap.c b/tools/testing/selftests/mm/hugepage-mremap.c >>> index b8f7d92e5a35..e611249080d6 100644 >>> --- a/tools/testing/selftests/mm/hugepage-mremap.c >>> +++ b/tools/testing/selftests/mm/hugepage-mremap.c >>> @@ -85,25 +85,14 @@ static void register_region_with_uffd(char *addr, size_t len) >>> if (ioctl(uffd, UFFDIO_API, &uffdio_api) == -1) >>> ksft_exit_fail_msg("ioctl-UFFDIO_API: %s\n", strerror(errno)); >>> >>> - /* Create a private anonymous mapping. The memory will be >>> - * demand-zero paged--that is, not yet allocated. When we >>> - * actually touch the memory, it will be allocated via >>> - * the userfaultfd. >>> - */ >>> - >>> - addr = mmap(NULL, len, PROT_READ | PROT_WRITE, >>> - MAP_PRIVATE | MAP_ANONYMOUS, -1, 0); >>> - if (addr == MAP_FAILED) >>> - ksft_exit_fail_msg("mmap: %s\n", strerror(errno)); >>> - >>> - ksft_print_msg("Address returned by mmap() = %p\n", addr); >>> - >>> - /* Register the memory range of the mapping we just created for >>> - * handling by the userfaultfd object. In mode, we request to track >>> - * missing pages (i.e., pages that have not yet been faulted in). >>> + /* Register the passed memory range for handling by the userfaultfd object. >> /* >> * ... >> >> While at it. >> >>> + * In mode, we request to track missing pages >>> + * (i.e., pages that have not yet been faulted in). >>> */ >>> if (uffd_register(uffd, addr, len, true, false, false)) >>> ksft_exit_fail_msg("ioctl-UFFDIO_REGISTER: %s\n", strerror(errno)); >>> + >>> + ksft_print_msg("Registered memory at address %p with userfaultfd\n", addr); >>> } >>> >>> int main(int argc, char *argv[]) >> Yes, that code is extremely weird. I wonder if this was some >> copy-and-paste from other uffd test code. >> >> Acked-by: David Hildenbrand (Arm) >> >> > Hi David, > > Yes, the test operates on hugetlb mappings created with > |MAP_HUGETLB | MAP_POPULATE|and sets up userfaultfd. Consequently, > registering it with |UFFDIO_REGISTER_MODE_MISSING| does not result in > any userfaults. > > Originally, the helper function created a separate anonymous mapping and > registered it with userfaultfd instead of the address supplied by the > caller. However, the test operates on hugetlb mappings, and the registered > anonymous mapping is never used in the |mremap()| path being exercised. > > Would it be better to remove userfaultfd registration entirely from this > test, since that path is not actually being tested? If it's tested with your change now (which I think that's what happenes), this is fine. It was just very weird before, because it tested something fairly unrelated. -- Cheers, David