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b=F+6m3z+xQ394skheiMjunzJhlBgB+CzilkptCdn5ktna0OC9prPxP1/JKJw82p+YI UXVqD0hCer/BB0QybutXjH03Y5iQs+hfrBjQIOsoUaUwmy4zCcGVTKTiD+3qLFeILI dJosqiE6T+i1kzFoqbVlDw9pf1t0BnX6hulULUji5sihczml9EFhDc/VCXiPMlB47N nn0n2fVF7KDRNWHHf6uD4hn09Uo+C96XSmN4PRA67PjSlObXIW+qgLxqzYFOm82NRZ x+UgPpKrUPQW82c2RprpiyLwOu2aYKuxRl1lSijFKgSHKXlSixB2r4swYDEj+GDr4H 7sD6NQXv88zBg== Date: Fri, 29 May 2026 17:45:24 +0100 From: Lorenzo Stoakes To: Dev Jain Cc: 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, 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 Subject: Re: [PATCH] fs/proc/task_mmu: do not warn on seeing non-migration pmd entry Message-ID: References: <20260529111704.1078346-1-dev.jain@arm.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20260529111704.1078346-1-dev.jain@arm.com> X-Stat-Signature: 6dqrsawq1qh43mj1efwytqwfa4f3j93d X-Rspamd-Server: rspam04 X-Rspamd-Queue-Id: 712E4A000E X-Rspam-User: X-HE-Tag: 1780073133-421469 X-HE-Meta: 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 X5EwkidL +gEEG0sElOfP2xdUN5+l5LsTByDI1ExOKWgbPJt+9cVR4FIbP7DU9VMoYzjNYPBrd82MY7ZKMcUz8EYUTDxlg2dlq8BOGzcyErkAYw8GnnYnVX1kQbclwvF9FtAz7SHl5RpYtf2NbXvD6d+ZtoimI8FTagdtzI928qDmmqASWGFtkPTsBpjJYPWN8Hd6dpRbkDm8GXdUNXt2n3Q/LYRQtB6kNQzjiJWwlegjvyuwivDHF3tW6asCKU+AtvajoP/dQv0BLeVTI3pjmS1CW5Cu9BawH88nBnK6Bhz8cPtlN2FxjflKj+1mjuw9Tfqn4ls80d8vhNLHVc6B8oAq262ds8mBPhI/up7wJeqSmcysUnoZqMMdD/cXPdK5IdVylnq8rbKs+tCCJ9UJSgyk0z8FNFQlP2NlSzfj22j9Yvcyu2wn3tN4= Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: List-Subscribe: List-Unsubscribe: On Fri, May 29, 2026 at 11:17:03AM +0000, 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); Thanks for this! though, hmm it really feels like you maybe want to add this as a test and make this a series :) Andrew is usually fine with adding tests as part of a fix I believe! > > > 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 The logic does seem sense, it does seem like something of an oversight here and I can repro the assert (though I have to fix something else first on my system, patch incoming for that...!) > --- > 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); > } > > -- > 2.43.0 > Cheers, Lorenzo