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Wed, 1 Apr 2026 14:18:44 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=k20201202; t=1775053128; bh=0FnBo7fPus+XeVOBCwP6OdIjz61MR23nw7pfxfUTbkc=; h=Date:Subject:To:Cc:References:From:In-Reply-To:From; b=s/xN6fs2yJMIi75Af4VCjehiyxEZsmoJQ/dqS8ELwDvfWNqLK0Oh0nrpjTi/dZTvg W8EbAq6AKWzEmQx9cBsNJ8X4u+2yVhTwe6VkTA2ZFqutURn2GpBUzcqk+SICdx+jbO WzkE7Aik2pUZUPoFyvIfYTZ1kescvgsDWF6Zo9I3Ks5YaRrg2/BVJp1QmVCOBoF0EE uh55q+/Z/0ouMbPzsc8Qtly3J7sqlD8G7luwMJ2GgUMcYPM+cdB34N/15q5S6LLOID rhtEKxlGOwrR1YwkBYjEe5LOkEGGxq/pa6O+dLRpe1dEiqPCFuVu4G0nrlQaEI1cor YezufykKlly+Q== Message-ID: <142f8c68-43c7-4a6a-bd2c-1c5ebda09b27@kernel.org> Date: Wed, 1 Apr 2026 16:18:43 +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: 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 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) -- Cheers, David