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 859D81A680A; Mon, 1 Jun 2026 05:49:03 +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=1780292944; cv=none; b=r4ybAnLF8GEllKmfoh0/F2U5BZuHAM1QmGPcSV0YO00fX5QX3uTUafKbiDfkp3KSwIhkpmLSazleFDtDrEBd+XFtt7AnMKylfMmjvCm8sYpJ8G8xdfXtaU+peB1ilhfLJaaVT8vddTgGsFPpVm3hXEqXFZhJMb43bIYH8QdsZBE= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1780292944; c=relaxed/simple; bh=LMRH2Q0qs4Wh1MT49HcBFprNUS8LcL1SIoD/fG6vfIg=; h=Message-ID:Date:MIME-Version:Subject:To:Cc:References:From: In-Reply-To:Content-Type; b=Gew3kHnAic1kvbz+gVyFiY1XdyGCvcMo/eW4H7gBg85qPkKrGC/LD6s7HZwJBrYBjltDWafZHbDh9lDsA8JQlcWlDdVdakZPGrPBcPPKoqiag/ZophxdAXavUVl6L8cqRY9FXvv3Jlx0BQMDQpU/bzv+Y5jvy7U4C3i2TdCd4cc= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b=jGYTIAjH; 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="jGYTIAjH" Received: by smtp.kernel.org (Postfix) with ESMTPSA id 654381F00893; Mon, 1 Jun 2026 05:48:58 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=kernel.org; s=k20260515; t=1780292943; bh=VpqqGQV4/Eyz5S8QpIkBPLCi6r5ufcIpCf3i736CDOw=; h=Date:Subject:To:Cc:References:From:In-Reply-To; b=jGYTIAjHQSbrm6posFzuL7i5KjhivxA56qf4ytkcfMVmowfejvF/uYtc6NOBbYWD0 xdr6MnmgyF84ZX3Tq5JKdRcwkPQArdGU/W+ZmpBIp7yBlQzR7yCY6KxhoK69TWBB86 TLqBdauE4vFalFq8LKceEFBtsVlKVcd4Zlz8/ZAuoH7x/+IYVuy/2aQ08T3oVRlWkK bpC0IihIgOWCzX5N9087um4S+xmFH92NnmF7djFYpC6VMsYB7YGrru+rFcquKim8Xf 1Xh4RBPV0v8HNEaB0up4VPITy3L7Jlx+3vs1RMMfOd09LZtKd86ogiZU7FzZn1tNCc hqXx+X45vtIpw== Message-ID: Date: Mon, 1 Jun 2026 07:48:56 +0200 Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH] fs/proc/task_mmu: do not warn on seeing non-migration pmd entry To: Dev Jain , akpm@linux-foundation.org, liam@infradead.org, ljs@kernel.org, jgg@ziepe.ca, leon@kernel.org, shuah@kernel.org Cc: vbabka@kernel.org, jannh@google.com, pfalcato@suse.de, rppt@kernel.org, surenb@google.com, mhocko@suse.com, balbirs@nvidia.com, linux-mm@kvack.org, linux-kernel@vger.kernel.org, linux-fsdevel@vger.kernel.org, linux-kselftest@vger.kernel.org, ryan.roberts@arm.com, anshuman.khandual@arm.com, stable@vger.kernel.org, Usama Arif References: <20260529111704.1078346-1-dev.jain@arm.com> <9d13d62f-df3d-46aa-8411-4abebb92c35e@arm.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 6/1/26 06:56, Dev Jain wrote: > > > On 01/06/26 12:41 am, David Hildenbrand (Arm) wrote: >> On 5/29/26 13:17, Dev Jain wrote: >>> pagemap_pmd_range_thp() warns if a non-present PMD is not a migration >>> entry. This became false once device-private entries at the PMD level were >>> added. >>> >>> One can hit the warning by patching hmm-tests.c with the following: >>> >>> diff --git a/tools/testing/selftests/mm/hmm-tests.c b/tools/testing/selftests/mm/hmm-tests.c >>> index e1c8a679a4cf3..7f0a3384f3c5f 100644 >>> --- a/tools/testing/selftests/mm/hmm-tests.c >>> +++ b/tools/testing/selftests/mm/hmm-tests.c >>> @@ -209,6 +209,37 @@ static int hmm_dmirror_cmd(int fd, >>> return 0; >>> } >>> >>> +static int hmm_read_self_pagemap(void *addr, unsigned long npages, >>> + unsigned long page_size) >>> +{ >>> + const size_t entry_size = sizeof(uint64_t); >>> + const off_t offset = ((uintptr_t)addr / page_size) * entry_size; >>> + uint64_t *entries; >>> + ssize_t nread; >>> + int fd; >>> + >>> + entries = malloc(npages * entry_size); >>> + if (!entries) >>> + return -ENOMEM; >>> + >>> + fd = open("/proc/self/pagemap", O_RDONLY); >>> + if (fd < 0) { >>> + free(entries); >>> + return -errno; >>> + } >>> + >>> + nread = pread(fd, entries, npages * entry_size, offset); >>> + close(fd); >>> + free(entries); >>> + >>> + if (nread < 0) >>> + return -errno; >>> + if ((size_t)nread != npages * entry_size) >>> + return -EIO; >>> + >>> + return 0; >>> +} >>> + >>> static void hmm_buffer_free(struct hmm_buffer *buffer) >>> { >>> if (buffer == NULL) >>> @@ -2314,6 +2345,10 @@ TEST_F(hmm, migrate_anon_huge_fault) >>> ASSERT_EQ(ret, 0); >>> ASSERT_EQ(buffer->cpages, npages); >>> >>> + /* Exercise pagemap on a PMD device-private entry. */ >>> + ret = hmm_read_self_pagemap(buffer->ptr, npages, self->page_size); >>> + ASSERT_EQ(ret, 0); >>> + >>> /* Check what the device read. */ >>> for (i = 0, ptr = buffer->mirror; i < size / sizeof(*ptr); ++i) >>> ASSERT_EQ(ptr[i], i); >>> >>> >> >> >>> Therefore, remove the stale migration-only assertion. >>> >>> Fixes: a30b48bf1b24 ("mm/migrate_device: implement THP migration of zone device pages") >>> Cc: stable@vger.kernel.org >>> Signed-off-by: Dev Jain >>> --- >>> Applies on mm-unstable (404fb4f38e8f). >>> >>> fs/proc/task_mmu.c | 1 - >>> 1 file changed, 1 deletion(-) >>> >>> diff --git a/fs/proc/task_mmu.c b/fs/proc/task_mmu.c >>> index 1e3a15bf46f4e..58938e62154d9 100644 >>> --- a/fs/proc/task_mmu.c >>> +++ b/fs/proc/task_mmu.c >>> @@ -2129,7 +2129,6 @@ static int pagemap_pmd_range_thp(pmd_t *pmdp, unsigned long addr, >>> flags |= PM_SOFT_DIRTY; >>> if (pmd_swp_uffd_wp(pmd)) >>> flags |= PM_UFFD_WP; >>> - VM_WARN_ON_ONCE(!pmd_is_migration_entry(pmd)); >>> page = softleaf_to_page(entry); >>> } >>> >> >> The whole thp_migration_supported() guard is a bit shaky, right? > > I think if you remove this, then you will trigger a WARN_ON in softleaf_to_page(), > for the case of !CONFIG_ARCH_ENABLE_THP_MIGRATION. Right, what I noted below. Right now it's all a bit hacked on top of initial migration entry support. >> >> I guess device-private entries currently imply thp_migration_supported(), but >> that thp_migration_supported() check is really questionable and should likely >> just go away (else if -> else). >> >> Staring at pte_to_pagemap_entry(), likely we'd also want >> >> if (softleaf_has_pfn(entry)) >> page = softleaf_to_page(entry); >> >> to prepare for PMD swap entries. > > Correct, and this is done in > https://lore.kernel.org/all/20260427100553.2754667-4-usama.arif@linux.dev/ > > I think in addition to that, Usama can also remove the thp_migration_supported() check. Yes, that one should go away. -- Cheers, David