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Wed, 1 Apr 2026 14:21:56 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=k20201202; t=1775053320; bh=Z33pYm24qbSvYLg3avP20eCSmcuudyAdxkucbIxFgJc=; h=Date:Subject:To:Cc:References:From:In-Reply-To:From; b=f801QttQuTDTdEug++TXlbPQYcGwCgqDN19BY676yqfaczi4em00rtie+1epsL2uV MhCJ7qmAWnh5SFl3tHZQi4yrsSvvaYgZu8/S56CJxizHoD4xCSPPOyNDKQhK1WgNun bQB2dzI1VOjGQ5BL3YOgMbmS/jIUXG6esDRtAp/7fqqCfSxCZcfruuF3rSoha8Wxzl Pjy5mpBddDIHQ9/Bn/R+HLjeQfhHcUxC48da58+1PICwZ7WDOUIMjkr7dC6E/MPo3e OnTv6usFWdMqfkzWa4bA666Z997TUHktcBwCkpMUyQ1u+drN4FEyoa36g71VySGYeK Fg92NM9zrxGpQ== Message-ID: Date: Wed, 1 Apr 2026 16:21:55 +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 08/13] selftests/mm: ensure destination is hugetlb-backed 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: <3b6ffba238a4b59de891acf896fa25d7d3193228.1774591179.git.sayalip@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 3/27/26 08:16, Sayali Patil wrote: > The hugepage-mremap selftest reserves the destination address using a > anonymous base-page mapping before calling mremap() with MREMAP_FIXED, > while the source region is hugetlb-backed. > > When remapping a hugetlb mapping into a base-page VMA may fail with: > > mremap: Device or resource busy > > This is observed on powerpc hash MMU systems where slice constraints > and page size incompatibilities prevent the remap. > That is weird. An mremap(MREMAP_FIXED) is really just an munmap() + move. Are we sure this is not some actual problem in the hugetlb implementation? > Ensure the destination region is created using MAP_HUGETLB so that both > source and destination VMAs are hugetlb-backed and compatible. Also add > MAP_POPULATE to the destination mapping to prefault hugepages, > matching the behaviour used for other hugetlb mapping in the test and > ensuring deterministic behaviour. But then the test suddenly requires more hugetlb pages, no? I don't see a good reason for the MAP_POPULATE, really. It will be discarded either way. > > Update the FLAGS macro to include MAP_HUGETLB | MAP_SHARED | > MAP_POPULATE so that both mappings are hugetlb-backed and compatible. > Also use the macro for the mmap() calls to avoid repeating > the flag combination. > > This ensures the test reliably exercises hugetlb mremap instead of > failing due to VMA type mismatch. > > Fixes: 12b613206474 ("mm, hugepages: add hugetlb vma mremap() test") > Acked-by: Zi Yan > Tested-by: Venkat Rao Bagalkote > Signed-off-by: Sayali Patil > --- > tools/testing/selftests/mm/hugepage-mremap.c | 11 ++++------- > 1 file changed, 4 insertions(+), 7 deletions(-) > > diff --git a/tools/testing/selftests/mm/hugepage-mremap.c b/tools/testing/selftests/mm/hugepage-mremap.c > index e611249080d6..48c24a4ba9a7 100644 > --- a/tools/testing/selftests/mm/hugepage-mremap.c > +++ b/tools/testing/selftests/mm/hugepage-mremap.c > @@ -31,7 +31,7 @@ > #define MB_TO_BYTES(x) (x * 1024 * 1024) > > #define PROTECTION (PROT_READ | PROT_WRITE | PROT_EXEC) > -#define FLAGS (MAP_SHARED | MAP_ANONYMOUS) > +#define FLAGS (MAP_HUGETLB | MAP_SHARED | MAP_POPULATE) > > static void check_bytes(char *addr) > { > @@ -121,23 +121,20 @@ int main(int argc, char *argv[]) > > /* mmap to a PUD aligned address to hopefully trigger pmd sharing. */ > unsigned long suggested_addr = 0x7eaa40000000; > - void *haddr = mmap((void *)suggested_addr, length, PROTECTION, > - MAP_HUGETLB | MAP_SHARED | MAP_POPULATE, fd, 0); > + void *haddr = mmap((void *)suggested_addr, length, PROTECTION, FLAGS, fd, 0); > ksft_print_msg("Map haddr: Returned address is %p\n", haddr); > if (haddr == MAP_FAILED) > ksft_exit_fail_msg("mmap1: %s\n", strerror(errno)); > > /* mmap again to a dummy address to hopefully trigger pmd sharing. */ > suggested_addr = 0x7daa40000000; > - void *daddr = mmap((void *)suggested_addr, length, PROTECTION, > - MAP_HUGETLB | MAP_SHARED | MAP_POPULATE, fd, 0); > + void *daddr = mmap((void *)suggested_addr, length, PROTECTION, FLAGS, fd, 0); > ksft_print_msg("Map daddr: Returned address is %p\n", daddr); > if (daddr == MAP_FAILED) > ksft_exit_fail_msg("mmap3: %s\n", strerror(errno)); > > suggested_addr = 0x7faa40000000; > - void *vaddr = > - mmap((void *)suggested_addr, length, PROTECTION, FLAGS, -1, 0); > + void *vaddr = mmap((void *)suggested_addr, length, PROTECTION, FLAGS, fd, 0); > ksft_print_msg("Map vaddr: Returned address is %p\n", vaddr); > if (vaddr == MAP_FAILED) > ksft_exit_fail_msg("mmap2: %s\n", strerror(errno)); -- Cheers, David