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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 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 X-Rspam-User: X-Rspamd-Server: rspam08 X-Rspamd-Queue-Id: 594E5A0006 X-Stat-Signature: yhsoqz549ape5rfiuu9sutab8bgw8oyy X-HE-Tag: 1780292944-429966 X-HE-Meta: U2FsdGVkX19tzX+3CuxFoA4XTe2H9Gr9Fa/k1icve627xK8bpPsrgG53M3C4NiAauXnMhVria91HyyH0yPfAOhcpCbrhSweGlmGZZeUdw4SVs8fBCi0MFaZ/Lw/JbU6I/wTCcUX1CT823QW3Uy5MsO6I3pvSjZM5qP8In9FRD/ZfFCOyHAIcclJro23Dc8WtQNRG/7Xcf/FdGyfKZFdku0lgl2Xg00QahKoumeA5OhU2pVyg5Tm43t1UGbWm0DHlTNd9xATIw6vSlEPlN5GyxSjBj4prPRaNbb2WA0yvl88sf3I8vuZbtgqVePs4zSfxKkg4B34NcdLO3yOBTxl52/rcCnWYgLvLGVVxSLpsrGaOXNR47V8tBTcmJf6nl9f1RMk1igIxvBIWc2kWDWo0nq/N3UMFSlF4HJPOE4RY06Jhg6Jf/0wvQLj9g0bCInXXDwPIRqn+h6w25j1JNU1urPRJlUeQGROzB/XkIjmIcq8dEl5gfYc63cao6Tbv/Vura0F6DoHfWFHYvrHEHDM+ikyEQjPVej/G5hCZA9Va9ZlBM9uXEkx3l6uBRI8/P992AnpQW4RJfAVmEVmm33Q8zevj0NsNF7w0UmHiJbXSRUO1AVDW157++SaRcb4/mqbOnMj2geE7Y3+LxsFmH4OuxtB5u2/Nfp8JG1uiOobQi/NGsOh1uf1ParlEf9mhLNlkQxBZF0HObS9Hykom9Rf0BQ1GIX5DY2nsSjaMUzV51I8yNI3fl8KUVcW5qWMuJAban34XwtZzIa9AtRFTR7uD3YPM4MdW+O3VeuH5gP5KHVevBt/xHNLNd3YdzW3VY2iRS98Zr9mvshbUEvcITgRre8B3X2aUTbqqjpcANXmiOei838Pf/jsAGxeBIe4kZnoMS8x9xIaqBZPPSOVmOFtkkP6wphkM9cNe2JfFMEUzH9c8Y9pGngkevaX5ylSpyjZEf1VOArrjSHZI843y1TM tZR1LPGj qGxsP39aMRjuSnJ0vumQb0S3cM7fh3yOOgWf+XU9dVj2njeU5XuT9S19NFmvdgYdzuKfL0BX4Jpij5z3JNnE7k6qf3q8hvDIBz2xlqwiP5YT7j+sF2/4WZsOSP+9VMJV2EB1SFHn2+OQrRVix8gC2/JmRFPyMQmoYmKA7dvJ3h3DK1AY0U9YCKHkmqKFPsueXVNkofmKH5zuFhCnU0J8hUN3Z8wj0hmS8Xb7TYX//uYjsDX84kib8249VJcsRj8bbVMkoH1W0X80LcsogLp22XOIzVy+I9K49En5cVWDtScs9tjmrUQZxr3ltEoI16rP0AHiyk9uQvs5Y7ka8wYm5J3KbbFAe/bqRD6Q+Qi0VoI95j/Gjx2Fi5s9zuxtUaoiX3ROC8krAJg334myW/1AC2OwbfmFNAR+BHgh1DVqbGQFX56Uyzd3h9D8Lqw== Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: List-Subscribe: List-Unsubscribe: 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