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bh=9TIi4e+jhWvSVLJqdtmuDmhXX3FHNuF+HLGG6Up3ljY=; c=simple/simple; d=linux.dev; h=from:to:subject:date:message-id:mime-version:content-type; s=key1; t=1793675312; v=1; x=1794280112; b=Y2iwAplloUzu5bm58twpXtkXG9/CIrmyyFjmR4r0iZ7mcki0wVTD3/AcJHdq+jFn4PndzStX io6vtdlQDs6nSNxk8e+ryodh7MtiPa/Xh/QOKBFWs0SWrKpNhZ4OClnOc5QavHY8x0cvltw7H2d 27+v3+F5MDZwhvhc2vc48Ozo= X-Envelope-To: linux-fsdevel@vger.kernel.org Received: by smtp.migadu.com with ESMTPS id 59608abf10f0d8e0; Tue, 03 Nov 2026 03:08:32 +0000 X-Mizu-Trace-ID: 59608abf10f0d8e0 X-Migadu-Flow: FLOW_OUT From: Lance Yang To: david@kernel.org Cc: akpm@linux-foundation.org, hannes@cmpxchg.org, mhocko@kernel.org, qi.zheng@linux.dev, shakeel.butt@linux.dev, ljs@kernel.org, kasong@tencent.com, baohua@kernel.org, axelrasmussen@google.com, yuanchu@google.com, weixugc@google.com, baoquan.he@linux.dev, baolin.wang@linux.alibaba.com, liam@infradead.org, vbabka@kernel.org, rppt@kernel.org, surenb@google.com, mhocko@suse.com, kees@kernel.org, peterz@infradead.org, jannh@google.com, pfalcato@suse.de, hughd@google.com, pasha.tatashin@soleen.com, pratyush@kernel.org, willy@infradead.org, jack@suse.cz, ziy@nvidia.com, lance.yang@linux.dev, riel@surriel.com, harry@kernel.org, apopple@nvidia.com, nico.pache@linux.dev, ryan.roberts@arm.com, dev.jain@arm.com, usama.arif@linux.dev, kas@kernel.org, matthew.brost@intel.com, jhubbard@nvidia.com, peterx@redhat.com, will@kernel.org, aneesh.kumar@kernel.org, npiggin@gmail.com, osalvador@suse.de, minchan@kernel.org, muchun.song@linux.dev, xu.xin@linux.dev, chengming.zhou@linux.dev, chrisl@kernel.org, shikemeng@huaweicloud.com, nphamcs@gmail.com, youngjun.park@lge.com, gourry@gourry.net, joshua.hahnjy@gmail.com, rakie.kim@sk.com, ying.huang@linux.alibaba.com, jgg@ziepe.ca, linux-mm@kvack.org, linux-kernel@vger.kernel.org, kexec@lists.infradead.org, linux-fsdevel@vger.kernel.org, linux-arch@vger.kernel.org, linux-cxl@vger.kernel.org, josef@toxicpanda.com, stable@vger.kernel.org, usama.anjum@arm.com Subject: Re: [PATCH v3 32/47] mm/mremap: fix moving PUD leaves Date: Tue, 3 Nov 2026 11:08:26 +0800 Message-ID: <20261103030826.79600-1-lance.yang@linux.dev> X-Mailer: git-send-email 2.49.0 In-Reply-To: <20261031-fixes_core-v3-32-d6437171ecc3@kernel.org> References: <20261031-fixes_core-v3-32-d6437171ecc3@kernel.org> X-Mailing-List: linux-fsdevel@vger.kernel.org List-Id: List-Post: List-Help: List-Subscribe: List-Unsubscribe: List-Owner: Precedence: list MIME-Version: 1.0 Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 8bit On Sat, Oct 31, 2026 at 10:40:01AM +0100, David Hildenbrand (Arm) wrote: >From: Josef Bacik > >pud_none_or_clear_bad() only really works on page tables. PUD leaves >confuse the check and make us clear the page table entry and print a >warning. > >Since commit aed877c2b4257 ("device/dax: properly refcount device dax pages >when mapping"), this also leaks device-DAX folio references, mapcounts >and RSS accounting, resulting in "Bad rss-counter state" warnings on exit. > >Allow PUD leaves in get_old_pud(). If a PUD leaf cannot be moved as a >whole or the move fails, split it. This unmaps it with proper accounting >instead of treating the leaf entry as a PMD table. > >Keep using pud_trans_huge() for now, in the future this code should be >cleaned up to just check for PUD leaves. > >Fix generated by an LLM and sent by Josef Bacik in private. > >Fixes: a00cc7d9dd93 ("mm, x86: add support for PUD-sized transparent hugepages") >Cc: stable@vger.kernel.org >Signed-off-by: Josef Bacik >Reviewed-by: Lorenzo Stoakes (ARM) >[ david: fallthrough after splitting ] >Reviewed-by: Pedro Falcato >Tested-by: Muhammad Usama Anjum >Signed-off-by: David Hildenbrand (Arm) >--- > mm/mremap.c | 9 ++++----- > 1 file changed, 4 insertions(+), 5 deletions(-) > >diff --git a/mm/mremap.c b/mm/mremap.c >index 91f0865f6aeea..1237718848f5c 100644 >--- a/mm/mremap.c >+++ b/mm/mremap.c >@@ -87,7 +87,7 @@ static pud_t *get_old_pud(struct mm_struct *mm, unsigned long addr) > return NULL; > > pud = pud_offset(p4d, addr); >- if (pud_none_or_clear_bad(pud)) >+ if (!pud_trans_huge(*pud) && pud_none_or_clear_bad(pud)) > return NULL; > > return pud; >@@ -847,11 +847,10 @@ unsigned long move_page_tables(struct pagetable_move_control *pmc) > if (!new_pud) > break; > if (pud_trans_huge(*old_pud)) { >- if (extent == HPAGE_PUD_SIZE) { >- move_pgt_entry(pmc, HPAGE_PUD, old_pud, new_pud); >- /* We ignore and continue on error? */ >+ if (extent == HPAGE_PUD_SIZE && >+ move_pgt_entry(pmc, HPAGE_PUD, old_pud, new_pud)) > continue; >- } >+ split_huge_pud(pmc->old, old_pud, pmc->old_addr); Right, copy_vma() already sets up the file and offset at the new address, so we can let subsequent faults rebuild the mapping. No need to build a PMD table just for the move ;) Reviewed-by: Lance Yang > } else if (IS_ENABLED(CONFIG_HAVE_MOVE_PUD) && extent == PUD_SIZE) { > if (move_pgt_entry(pmc, NORMAL_PUD, old_pud, new_pud)) > continue; > >-- >2.43.0 > >