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h=Date:Subject:To:Cc:References:From:In-Reply-To:From; b=HaUyy/Q3QQY8LFo0HHWNssQu++Ryy4dWmAHD4fasvlTInFEZouDCQj/vtZBX+P2ZC VtrFIsX83pVwwuosFxTpDu3u1Et3kGCE7TcgrBQlrgqw5orWkEXPYGukRONyM8mxS9 fpXC/jZe5fUPVnPzy7oIKCbV0BibT+oV/WFEDKT4= Message-ID: <9d13d62f-df3d-46aa-8411-4abebb92c35e@arm.com> Date: Mon, 1 Jun 2026 10:26:45 +0530 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: "David Hildenbrand (Arm)" , 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 References: <20260529111704.1078346-1-dev.jain@arm.com> Content-Language: en-US From: Dev Jain In-Reply-To: Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 7bit X-Rspamd-Server: rspam11 X-Stat-Signature: coqn45csjaphkpdkudrmzzfck3ew456w X-Rspamd-Queue-Id: 567D040004 X-Rspam-User: X-HE-Tag: 1780289816-361171 X-HE-Meta: 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 FRpyK8rY m4JV+ZMQ41H1GUMUcuOFWJNIp4+V71ncc1U63y29XTMocLFCf5cNh8pul46xonPulRgHLSnYixUSyKOra2g/CgtSeYHwe69PY0TniP4+SqYA22J30VE5nohKy34aBPUjZmNQwc7WF0HDajIaUQcMuDLcPyV4fSWev3x24/SB4RYYZlnt9t2nGiRlGvSFXqpLywrP2FgXl6xT3VWhaXSB4T87WQp3dKITN5hb1yp/LgKvNkOSQ/zq7jHYkQ3sIkcPQz/MhTF8IQ9daCff/iyh/y7+vMRt63ZL1UhvfHt+pJFLY74kySgUAyi8Mqo3di5Rn7IrGRO2aMhN7pE61jADr9xy8s+B+t6FoNwn6cFgqsBKfKE8d6klBUMLyMXjQHpT7Jm3ydHjNOTlTsuMFSzC225EI6UO172sfKcc6 Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: List-Subscribe: List-Unsubscribe: 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. > > 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. > > > Anyhow, both are unrelated (can you send patches to clean it up?) > > Acked-by: David Hildenbrand (Arm) >