From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from smtp.kernel.org (aws-us-west-2-korg-mail-alma10-1.taild15c8.ts.net [100.103.45.18]) (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 957E714A62B; Mon, 1 Jun 2026 08:35:09 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=100.103.45.18 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1780302910; cv=none; b=ZF/vUBWR4atSvndavNjS30sgNqIOrM50C/lPDzxKc5U+S12rLsqiaV4pmLHhNGmSkkfEUjb1TdNK0zPkdb/qhxMofJI+dc4wVIAz7Er8ndROfeTo9iUZ6F2Gg4VZYJxV8/621JvpkYoM2VLfigS1v4BZ4uQpgnU8whOccczBclY= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1780302910; c=relaxed/simple; bh=7qIZ94fwyarOEIYhxdn6d8BHBpOVWkVbQ57Fwh3IZT4=; h=Date:From:To:Cc:Subject:Message-ID:References:MIME-Version: Content-Type:Content-Disposition:In-Reply-To; b=ICg1RKC7Yf7hOlpHb1ySFzAK26TyKtWqTb125d7DePMgwCtZhNh0teCuTkvQHA+dKfC8/WKgAyN2H2NkSKtvurhk+PUQGi06VKhzxmcnzYp9yPYPjPl2I9TkR4vYlI89yxVOlSw++zHYho+Vu/3Oww/xVPbejT+cbnBRFq1NOGc= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b=VuqXDHST; arc=none smtp.client-ip=100.103.45.18 Authentication-Results: smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b="VuqXDHST" Received: by smtp.kernel.org (Postfix) with ESMTPSA id 5C6C01F00893; Mon, 1 Jun 2026 08:35:04 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=kernel.org; s=k20260515; t=1780302909; bh=9lDbQeKLavZFIEOh/CkUOUIvMQqnzPuvTdfWQRXAjQY=; h=Date:From:To:Cc:Subject:References:In-Reply-To; b=VuqXDHSTvMpQFKI7KSl1aqVO8mINRprGN9VK5lUG2VU8Ww3vKfBDSmWFtvv6k21sD TaxevY6IVRKCqJsGi7U3D+UvH2idaNRUj6mqc9Uq/x/vnnJEhntZNT8CEOSe/NjDrd 0tbukliX6py74YT/0bsXvRAcipY7vwFycxesA4iNJRMPcxH3WIAcWrXO4J3xnWJOvK 5nJFQpjt7ankRRWAyAVnYgK4xCpXkHH15zu1sqCAwWrClnvu88KdV0qyZDKNdwq+b7 ms3vkIZD2ZEX4qo2drY08GUi6G9clbW7rHWN3mTok83U3ARC9Lfthrv2DVl2ZfhHlK iVcOSRuSLzvDw== Date: Mon, 1 Jun 2026 09:35:01 +0100 From: Lorenzo Stoakes To: Dev Jain Cc: Balbir Singh , akpm@linux-foundation.org, liam@infradead.org, jgg@ziepe.ca, leon@kernel.org, david@kernel.org, shuah@kernel.org, vbabka@kernel.org, jannh@google.com, pfalcato@suse.de, linux-mm@kvack.org, linux-kernel@vger.kernel.org, linux-fsdevel@vger.kernel.org, rppt@kernel.org, surenb@google.com, mhocko@suse.com, linux-kselftest@vger.kernel.org, usama.arif@linux.dev, ryan.roberts@arm.com, anshuman.khandual@arm.com Subject: Re: [PATCH v2 2/2] selftests/mm/hmm-tests: test pagemap reads of PMD device-private entries Message-ID: References: <20260530085413.1270139-1-dev.jain@arm.com> <20260530085413.1270139-3-dev.jain@arm.com> <9d8bffb5-bb07-4cde-8a20-8b9b9996f8cf@nvidia.com> <7750de96-44c6-47b0-b0a9-dd948fca2e90@arm.com> Precedence: bulk X-Mailing-List: linux-fsdevel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <7750de96-44c6-47b0-b0a9-dd948fca2e90@arm.com> On Mon, Jun 01, 2026 at 10:40:48AM +0530, Dev Jain wrote: > > > On 01/06/26 5:39 am, Balbir Singh wrote: > > On 5/30/26 18:54, Dev Jain wrote: > >> To cover pagemap paths scanning PMD entries, add assertions to check > >> whether a device-private PMD entry has the correct pagemap information - > >> the PM_SWAP bit must be on in the pagemap entry. Before that, we must > >> assert through HMM_DMIRROR_SNAPSHOT snapshot that the leaf entry is > >> at PMD level and not PTE level. > >> > >> Signed-off-by: Dev Jain > >> --- > >> tools/testing/selftests/mm/hmm-tests.c | 29 ++++++++++++++++++++++++++ > >> 1 file changed, 29 insertions(+) > >> > >> diff --git a/tools/testing/selftests/mm/hmm-tests.c b/tools/testing/selftests/mm/hmm-tests.c > >> index e1c8a679a4cf3..d09d4a9081de1 100644 > >> --- a/tools/testing/selftests/mm/hmm-tests.c > >> +++ b/tools/testing/selftests/mm/hmm-tests.c > >> @@ -2276,8 +2276,11 @@ TEST_F(hmm, migrate_anon_huge_fault) > >> unsigned long npages; > >> unsigned long size; > >> unsigned long i; > >> + unsigned char *m; > >> + uint64_t entry; > >> void *old_ptr; > >> void *map; > >> + int pagemap_fd; > >> int *ptr; > >> int ret; > >> > >> @@ -2318,6 +2321,32 @@ TEST_F(hmm, migrate_anon_huge_fault) > >> for (i = 0, ptr = buffer->mirror; i < size / sizeof(*ptr); ++i) > >> ASSERT_EQ(ptr[i], i); > >> > >> + if (!hmm_is_coherent_type(variant->device_number)) { > >> + ret = hmm_dmirror_cmd(self->fd, HMM_DMIRROR_SNAPSHOT, > >> + buffer, npages); > >> + ASSERT_EQ(ret, 0); > >> + ASSERT_EQ(buffer->cpages, npages); > >> + > >> + m = buffer->mirror; > >> + for (i = 0; i < npages; ++i) > >> + ASSERT_EQ(m[i], HMM_DMIRROR_PROT_DEV_PRIVATE_LOCAL | > >> + HMM_DMIRROR_PROT_WRITE | > >> + HMM_DMIRROR_PROT_PMD); > > > > madvise(..., MADV_HUGEPAGE) is not sufficient to guarantee that the allocation > > was indeed converted to THP. Might be worth using the kpageflags interface (but that > > requires elevated privileges) and then KPF_THP? Otherwise the HMM_DMIRROR_PROT_PMD > > can be a miss from time to time. One other option is not to assert, but to check > > and inform? > > I'll then use the existing check_huge_anon() to assert that a PMD THP got allocated. Would MADV_COLLAPSE work here? > > > > >> + > >> + pagemap_fd = open("/proc/self/pagemap", O_RDONLY); > >> + ASSERT_GE(pagemap_fd, 0); > >> + > >> + for (i = 0; i < npages; ++i) { > >> + entry = pagemap_get_entry(pagemap_fd, > >> + (char *)buffer->ptr + i * self->page_size); > >> + > > > > If this is a THP entry, do we have valid pagemap entries for offset of i * page_size? > > Yep we do, see the populate_pagemap label in pagemap_pmd_range_thp. > > > > >> + ASSERT_NE(entry & PM_SWAP, 0); > >> + ASSERT_EQ(entry & PM_PRESENT, 0); > > > > Nit: You can use PAGEMAP_PRESENT() > > Okay. > > > > >> + } > >> + > >> + close(pagemap_fd); > >> + } > >> + > >> /* Fault pages back to system memory and check them. */ > >> for (i = 0, ptr = buffer->ptr; i < size / sizeof(*ptr); ++i) > >> ASSERT_EQ(ptr[i], i); > > > > Balbir Singh > Cheers, Lorenzo