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[99.254.114.190]) by smtp.gmail.com with ESMTPSA id 6a1803df08f44-6e20514ee9bsm694376d6.30.2025.01.23.09.40.38 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Thu, 23 Jan 2025 09:40:39 -0800 (PST) Date: Thu, 23 Jan 2025 12:40:36 -0500 From: Peter Xu To: Ryan Roberts Cc: Andrew Morton , Muchun Song , "Liam R. Howlett" , Lorenzo Stoakes , Vlastimil Babka , Jann Horn , Shuah Khan , David Hildenbrand , =?utf-8?Q?Miko=C5=82aj?= Lenczewski , Mark Rutland , linux-kernel@vger.kernel.org, linux-mm@kvack.org, linux-kselftest@vger.kernel.org, stable@vger.kernel.org Subject: Re: [PATCH v1 1/2] mm: Clear uffd-wp PTE/PMD state on mremap() Message-ID: References: <20250107144755.1871363-1-ryan.roberts@arm.com> <20250107144755.1871363-2-ryan.roberts@arm.com> <850479be-000a-45a7-9669-491d4200a988@arm.com> Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Type: text/plain; charset=utf-8 Content-Disposition: inline In-Reply-To: <850479be-000a-45a7-9669-491d4200a988@arm.com> On Thu, Jan 23, 2025 at 02:38:46PM +0000, Ryan Roberts wrote: > > @@ -5470,7 +5471,18 @@ static void move_huge_pte(struct vm_area_struct *vma, unsigned long old_addr, > > spin_lock_nested(src_ptl, SINGLE_DEPTH_NESTING); > > > > pte = huge_ptep_get_and_clear(mm, old_addr, src_pte); > > - set_huge_pte_at(mm, new_addr, dst_pte, pte, sz); > > + > > + if (need_clear_uffd_wp && pte_marker_uffd_wp(pte)) > > + huge_pte_clear(mm, new_addr, dst_pte, sz); > > This is checking if the source huge_pte is a uffd-wp marker and clearing the > destination if so. The destination could have previously held arbitrary valid > mappings, I guess? I think it should be all cleared. I didn't check all mremap paths, but for MREMAP_FIXED at least there should be: if (flags & MREMAP_FIXED) { /* * In mremap_to(). * VMA is moved to dst address, and munmap dst first. * do_munmap will check if dst is sealed. */ ret = do_munmap(mm, new_addr, new_len, uf_unmap_early); if (ret) goto out; } It also doesn't sound right to leave anything in dest range, e.g. if there can be any leftover dest ptes in move_page_tables(), then it means HPAGE_P[MU]D won't work, as they install huge entries directly. For that I do see a hint in the comment too in that path: move_normal_pud(): /* * The destination pud shouldn't be established, free_pgtables() * should have released it. */ if (WARN_ON_ONCE(!pud_none(*new_pud))) return false; PMD path has similar implications. Thanks, -- Peter Xu