From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from smtp.kernel.org (aws-us-west-2-korg-mail-1.web.codeaurora.org [10.30.226.201]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by smtp.subspace.kernel.org (Postfix) with ESMTPS id 5F56036BCC8; Thu, 26 Feb 2026 16:29:56 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=10.30.226.201 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1772123396; cv=none; b=o7bQEu8WxkVzkwZJ1xJuVq20w+YPP/5MP2DvGA+Pu6Da7viWVTNeZZDWi4NEGID+4PPI4wHSyk+D7Ikxke2GDt8WfV6GKGn9OB3jvt+cUmRTSjpOw+NT61ziH9TjghSQieqJ9fhrVFjPYLNJ/MwByZ3fPkUHsOsMDbkxgg//mQw= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1772123396; c=relaxed/simple; bh=uMFN9RkMbM+7SbXyhkLLyz3IvEzev7M+UJI2j68H1GU=; h=Message-ID:Date:MIME-Version:Subject:To:Cc:References:From: In-Reply-To:Content-Type; b=s9eYIEvgDSlkxHgJqKqMnlkjrXPrEIUWsejstRcmJa+5Qehezz43Q0n+mzNirKBvq59UctnYtXNeMZ/ciH2Ie1SN44coQ3Aoh/Ah8Tw164janWM/URj2T2YpR+SZqWOlv526mvtp+i34fyYM4tvxRISQ3IuZK9V4/7KYgvT2Fbw= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b=OB3FKG2X; arc=none smtp.client-ip=10.30.226.201 Authentication-Results: smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b="OB3FKG2X" Received: by smtp.kernel.org (Postfix) with ESMTPSA id 519A4C116C6; Thu, 26 Feb 2026 16:29:54 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=k20201202; t=1772123396; bh=uMFN9RkMbM+7SbXyhkLLyz3IvEzev7M+UJI2j68H1GU=; h=Date:Subject:To:Cc:References:From:In-Reply-To:From; b=OB3FKG2XQBSFfNl6yatDDLwkubGI3MTeie/zNm8/qluN6mhVq7k9oZd6suBLz8So2 mlXSyzGb4JjZkOe0yU1+kIdE2dygihuvnRdZJPvYuUhP+qDchhw5aUOabPa+90pPcx G9m1RMch34bOWQkpgakTvl0tQD53nVdMOM6tkN7yYCbyC2/HwNLHzE3PTPuUg0UN3l 3lfjaRVHX2n4RXWidrSrCFN+aPduJNuWAfZifP3NofAopZvQXDrIVghRcCN8UGGjGf SdamrQWFZfXGcySWnN1d5qiVmwA4jx1gcHocmJhZrcBnE1Y1XxPFWyPHEJA6AGNB18 tJsCRrNyw/jVw== Message-ID: Date: Thu, 26 Feb 2026 17:29:51 +0100 Precedence: bulk X-Mailing-List: stable@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH v2 3/3] selftests/mm: Add UFFDIO_MOVE huge zeropage PMD regression test To: Chris Down , Andrew Morton Cc: Matthew Wilcox , kernel-team@fb.com, linux-mm@kvack.org, linux-kernel@vger.kernel.org, stable@vger.kernel.org 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 2/26/26 15:18, Chris Down wrote: > The existing uffd-unit-tests move-pmd coverage exercises PMD-sized > UFFDIO_MOVE on anonymous THPs, but it does not force the huge zeropage > PMD path in move_pages_huge_pmd(). > > Add a dedicated anonymous UFFDIO_MOVE PMD test that exercises this > relatively comprehensively. > > Signed-off-by: Chris Down > --- > tools/testing/selftests/mm/uffd-unit-tests.c | 176 +++++++++++++++++++ > 1 file changed, 176 insertions(+) > > diff --git a/tools/testing/selftests/mm/uffd-unit-tests.c b/tools/testing/selftests/mm/uffd-unit-tests.c > index 6f5e404a446c..372619e3906d 100644 > --- a/tools/testing/selftests/mm/uffd-unit-tests.c > +++ b/tools/testing/selftests/mm/uffd-unit-tests.c > @@ -203,6 +203,62 @@ static int pagemap_open(void) > return fd; > } > Thanks for implementing this! [...] > +static bool uffd_pagemap_scan_get_categories(int fd, char *start, uint64_t *categories) > +{ > + struct page_region r = { 0 }; > + long ret; > + > + if (!uffd_pagemap_scan_supported(fd, start)) > + return false; > + > + ret = uffd_pagemap_scan_get_categories_raw(fd, start, &r); > + if (ret < 0) > + err("PAGEMAP_SCAN failed: %s", strerror(errno)); > + > + *categories = ret ? r.categories : 0; > + return true; > +} Can we unify (deduplicate) that code with what we have in vm_util.c, and then only export a function like bool pagemap_is_huge_zero(int fd, char *start) similar to pagemap_is_softdirty() etc to be consumed by the test here? It can simply return "false" in case the interface is not available. > + > /* This macro let __LINE__ works in err() */ > #define pagemap_check_wp(value, wp) do { \ > if (!!(value & PM_UFFD_WP) != wp) \ > @@ -1227,6 +1283,119 @@ static void uffd_move_pmd_test(uffd_global_test_opts_t *gopts, uffd_test_args_t > uffd_move_pmd_handle_fault); > } > > +static void uffd_move_pmd_huge_zeropage_test(uffd_global_test_opts_t *gopts, > + uffd_test_args_t *targs) > +{ > + unsigned long pmd_size = read_pmd_pagesize(); > + unsigned long pmd_pages; > + unsigned long bytes = gopts->nr_pages * gopts->page_size; > + char *orig_area_src = gopts->area_src, *orig_area_dst = gopts->area_dst; > + char *aligned_src, *aligned_dst; > + unsigned long src_offs, dst_offs, max_offs; > + pthread_t uffd_mon; > + struct uffd_args args = { 0 }; > + char c = '\0'; > + int pagemap_fd; > + uint64_t categories; > + unsigned long i; > + > + if (pmd_size <= gopts->page_size) { > + uffd_test_skip("huge page size is 0, feature missing?"); > + return; > + } > + if (!detect_huge_zeropage()) { > + uffd_test_skip("transparent huge zeropage disabled"); > + return; > + } > + > + pmd_pages = pmd_size / gopts->page_size; > + if (bytes < pmd_size) { > + uffd_test_skip("not enough pages for one PMD-sized move"); > + return; > + } > + > + aligned_src = ALIGN_UP(orig_area_src, pmd_size); > + aligned_dst = ALIGN_UP(orig_area_dst, pmd_size); > + src_offs = (aligned_src - orig_area_src) / gopts->page_size; > + dst_offs = (aligned_dst - orig_area_dst) / gopts->page_size; > + max_offs = src_offs > dst_offs ? src_offs : dst_offs; > + if (max_offs + pmd_pages > gopts->nr_pages) { > + uffd_test_skip("could not find aligned PMD-sized src/dst window"); > + return; > + } > + > + if (madvise(orig_area_dst, bytes, MADV_HUGEPAGE)) > + err("madvise(MADV_HUGEPAGE) failure"); > + if (madvise(orig_area_src, bytes, MADV_DONTFORK)) > + err("madvise(MADV_DONTFORK) failure"); > + if (madvise(aligned_src, pmd_size, MADV_DONTNEED)) > + err("madvise(MADV_DONTNEED) failure"); > + > + /* Materialise a PMD-sized huge zeropage mapping in the source. */ "Fault in the huge zeropage" > + force_read_pages(aligned_src, pmd_pages, gopts->page_size); > + > + pagemap_fd = pagemap_open(); > + if (!uffd_pagemap_scan_get_categories(pagemap_fd, aligned_src, &categories)) { > + close(pagemap_fd); > + uffd_test_skip("PAGEMAP_SCAN unsupported"); > + return; > + } > + if ((categories & (PAGE_IS_PRESENT | PAGE_IS_PFNZERO | PAGE_IS_HUGE)) != > + (PAGE_IS_PRESENT | PAGE_IS_PFNZERO | PAGE_IS_HUGE)) { > + close(pagemap_fd); > + uffd_test_skip("could not materialise a huge zeropage PMD mapping"); "could not fault in the huge zeropage" ? > + return; > + } > + gopts->area_src = aligned_src; > + gopts->area_dst = aligned_dst; > + > + if (uffd_register(gopts->uffd, gopts->area_dst, pmd_size, true, false, false)) > + err("register failure"); > + > + args.gopts = gopts; > + args.handle_fault = uffd_move_pmd_handle_fault; > + if (pthread_create(&uffd_mon, NULL, uffd_poll_thread, &args)) > + err("uffd_poll_thread create"); > + > + /* > + * One fault on dst should trigger a single PMD-sized UFFDIO_MOVE from > + * the huge zeropage PMD we populated in the source. > + */ > + force_read_pages(gopts->area_dst, pmd_pages, gopts->page_size); > + > + if (write(gopts->pipefd[1], &c, sizeof(c)) != sizeof(c)) > + err("pipe write"); > + if (pthread_join(uffd_mon, NULL)) > + err("join() failed"); > + > + if (args.missing_faults != 1 || args.minor_faults != 0) { > + uffd_test_fail("stats check error"); > + } else if (!uffd_pagemap_scan_get_categories(pagemap_fd, gopts->area_dst, > + &categories)) { > + uffd_test_fail("PAGEMAP_SCAN unsupported"); Why should it suddenly be unsupported when it worked before? With the pagemap_is_huge_zero() helper, this will boil down to } else if (pagemap_is_huge_zero(...)) { uffd_test_fail("moved destination is not a huge zeropage PMD"); } > + } else if ((categories & (PAGE_IS_PRESENT | PAGE_IS_PFNZERO | > + PAGE_IS_HUGE)) != > + (PAGE_IS_PRESENT | PAGE_IS_PFNZERO | PAGE_IS_HUGE)) { > + uffd_test_fail("moved destination is not a huge zeropage PMD"); > + } else if (!check_huge_anon(gopts->area_dst, 0, pmd_size)) { > + /* vm_normal_page_pmd() must continue to treat the moved PMD as special. */ > + uffd_test_fail("moved huge zeropage PMD counted as AnonHugePages"); > + } else { > + for (i = 0; i < pmd_size; i++) { > + if (gopts->area_dst[i]) { > + uffd_test_fail("moved huge zeropage PMD data is not zero"); > + goto out_restore; > + } > + } That's a bit excessive given that pagemap told us that it is indeed the huge zeropage. So I would just drop this. -- Cheers, David