From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from smtp.kernel.org (aws-us-west-2-korg-mail-alma10-1.taild15c8.ts.net [100.103.45.18]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by smtp.subspace.kernel.org (Postfix) with ESMTPS id 213393537DE; Mon, 25 May 2026 11:38:34 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=100.103.45.18 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1779709115; cv=none; b=dcG4UlCaEQQuvX7HNWjwW+DCTd1ll/RQrq8RC7VC4bpsawY3SVh/1/QCCmeGIruoQRXRqWC74JlYYx5MSYTBGBVInoif0wUUMCnA/MfIp8nRf3q5DSXmlc+qwL0UVfKQ2LMZ3HdXJurXTPsfRFPKAQEfi9E4/F7pcWWEgGf+iW0= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1779709115; c=relaxed/simple; bh=nH+DV8TMFPp7poGzqh3KlZ+MSgriT4DZeEGWEghoZfs=; h=From:To:Cc:Subject:Date:Message-ID:In-Reply-To:References: MIME-Version; b=FxFal5B3ju/4UwenoyZFS7zc8BQgLY6bJm0LB4R+q+pabrv5erPLDLHuV0SVr854/wR9J9F1xLt/9n9tbkR7+YnXpD0FOk/jLg9FU7Plvebz9sPfgyT+n8yGAyDRQjQMXD24Z/gEwwjIk476MK7DisQbT98jWt8ZZHb2pkEqlao= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b=B4TI8cud; arc=none smtp.client-ip=100.103.45.18 Authentication-Results: smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b="B4TI8cud" Received: by smtp.kernel.org (Postfix) with ESMTPSA id 578841F00A3A; Mon, 25 May 2026 11:38:33 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=kernel.org; s=k20260515; t=1779709114; bh=YaYAA4LDLxQSQ00+eYpFUK2Ea0ShPnS1Md5Dkd+3h9c=; h=From:To:Cc:Subject:Date:In-Reply-To:References; b=B4TI8cudOEvvDk93negGtfyvd5qJ9xp3iSk3lMQKduCGEW8fFGLdp9vptusOSMcby j4BgXNnfKvRApU1ah7inTu7JyU9HfPmlfwkNA51ATJIHh7Kc2VUotCuzOSSyd8NnSK xRH9LureLXAPaj7KeWKOGJeESVprFuMBuwi+LtxKgbwuaJlzQqsDzLh8J2j5XHIWic WbkEt1ScXUw4BKbb4Eb6gA9rZeKfyI+91hcl2kwqLR027iRKmj2l+s3JJ5LagozIdu ghGzyer4o1DghJ28vcIvSIWz6VC56J1DRwEOdQojrvmnAKKaue6GCZhvwumFsmQLme EQBiMsiAs9D9Q== Received: from phl-compute-03.internal (phl-compute-03.internal [10.202.2.43]) by mailfauth.phl.internal (Postfix) with ESMTP id B6979F40082; Mon, 25 May 2026 07:38:32 -0400 (EDT) Received: from phl-frontend-03 ([10.202.2.162]) by phl-compute-03.internal (MEProxy); Mon, 25 May 2026 07:38:32 -0400 X-ME-Sender: X-ME-Received: X-ME-Proxy-Cause: dmFkZTE8BdsnOcJoKEIc8nWENdzZ3IJcc78XaZb937JZptTbBfsj35uOLLco64YanRFUy/ vxRRXxJncUkkFhQ6Fw9JoTXNpIBZaIk7PJKSogIAKlou1fnKpK60SVEE9wIdCSKeJSiEmd jMYcCTSecv2wdbvACcZ3jQHh2R35wiBKAXeBalxbQ8obtaPzZg26qqKn3eo1ycSESHvZEY 8vksW44pxFuJVzxfC4xrmaM24Xz/fIt3AP98RkQGIoAMYfpB8FzSca86T9jBGlmKI9r1LK Ip3BvhMbIznxq4KZmZ20/tINtDmxtvyOkjCcERfRzx2DQnK/TIBWkODYKxc/0O8u9p7eJa T6hUf/mJ+nZsoYTOiz1Cb2+KAyyLn0R/R3r0RXsTw92y0vMFHqj4tuch0BcWUJnAgHF7i/ +IlIGXUBbqz9Bx7N+IqZu0eIRx/QKzC+NGbTOHcutWN62zk4j/RMaPb+JSnw6d6T93R7WZ EVhNnroNs/TZuBT1WuQkCYX+SZ2FzCIAie68u4T2p1kMzTZgpZz1ffVrOpTkSTeM9TTw7J 5PoA0rJUHkWCHnmr3yBrOogvJhpyOE0hIjyRmOMgfWE1IzSRJqTy2GvZ5LPWm3UqHW07RR ozbHcuNNmRTa7lzT7rTHgZPmXovuzFqMR7wOx+AlXANnURdOGf+6g5b4XZtQ X-ME-Proxy: Feedback-ID: i10464835:Fastmail Received: by mail.messagingengine.com (Postfix) with ESMTPA; Mon, 25 May 2026 07:38:30 -0400 (EDT) From: "Kiryl Shutsemau (Meta)" To: akpm@linux-foundation.org, rppt@kernel.org, peterx@redhat.com, david@kernel.org Cc: ljs@kernel.org, surenb@google.com, vbabka@kernel.org, Liam.Howlett@oracle.com, ziy@nvidia.com, corbet@lwn.net, skhan@linuxfoundation.org, seanjc@google.com, pbonzini@redhat.com, jthoughton@google.com, aarcange@redhat.com, sj@kernel.org, usama.arif@linux.dev, linux-mm@kvack.org, linux-kernel@vger.kernel.org, linux-doc@vger.kernel.org, linux-kselftest@vger.kernel.org, kvm@vger.kernel.org, kernel-team@meta.com, "Kiryl Shutsemau (Meta)" Subject: [PATCH v4 05/14] mm: add MM_CP_UFFD_RWP change_protection() flag Date: Mon, 25 May 2026 12:37:19 +0100 Message-ID: <20260525113737.1942478-6-kas@kernel.org> X-Mailer: git-send-email 2.54.0 In-Reply-To: <20260525113737.1942478-1-kas@kernel.org> References: <20260525113737.1942478-1-kas@kernel.org> Precedence: bulk X-Mailing-List: linux-doc@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Transfer-Encoding: 8bit Preparatory patch. Add the change_protection() primitive that userfaultfd RWP will use. An RWP-protected PTE is PAGE_NONE with the uffd PTE bit set. The PROT_NONE half makes the CPU fault on any access; the uffd bit distinguishes an RWP fault from a plain mprotect(PROT_NONE) or NUMA hinting fault. MM_CP_UFFD_WP and MM_CP_UFFD_RWP share the same PTE bit, so the two cannot be used together on the same range. Two new change_protection() flags: MM_CP_UFFD_RWP install PAGE_NONE and set the uffd bit MM_CP_UFFD_RWP_RESOLVE restore vma->vm_page_prot, clear the uffd bit Both are wired through change_pte_range(), change_huge_pmd(), and hugetlb_change_protection() so anon, shmem, THP, and hugetlb all share the same semantics. Signed-off-by: Kiryl Shutsemau Assisted-by: Claude:claude-opus-4-6 Reviewed-by: Mike Rapoport (Microsoft) --- include/linux/mm.h | 5 ++++ include/linux/userfaultfd_k.h | 1 - mm/huge_memory.c | 30 +++++++++++++---------- mm/hugetlb.c | 25 ++++++++++++++----- mm/mprotect.c | 46 +++++++++++++++++++++++++++-------- 5 files changed, 77 insertions(+), 30 deletions(-) diff --git a/include/linux/mm.h b/include/linux/mm.h index 3d0a5ac3c717..ecbf3e83a892 100644 --- a/include/linux/mm.h +++ b/include/linux/mm.h @@ -3286,6 +3286,11 @@ int get_cmdline(struct task_struct *task, char *buffer, int buflen); #define MM_CP_UFFD_WP_RESOLVE (1UL << 3) /* Resolve wp */ #define MM_CP_UFFD_WP_ALL (MM_CP_UFFD_WP | \ MM_CP_UFFD_WP_RESOLVE) +/* Whether this change is for uffd RWP */ +#define MM_CP_UFFD_RWP (1UL << 4) /* do rwp */ +#define MM_CP_UFFD_RWP_RESOLVE (1UL << 5) /* resolve rwp */ +#define MM_CP_UFFD_RWP_ALL (MM_CP_UFFD_RWP | \ + MM_CP_UFFD_RWP_RESOLVE) bool can_change_pte_writable(struct vm_area_struct *vma, unsigned long addr, pte_t pte); diff --git a/include/linux/userfaultfd_k.h b/include/linux/userfaultfd_k.h index 87a8cebd5938..16fbe11c0c55 100644 --- a/include/linux/userfaultfd_k.h +++ b/include/linux/userfaultfd_k.h @@ -361,7 +361,6 @@ static inline bool userfaultfd_huge_pmd_wp(struct vm_area_struct *vma, return false; } - static inline bool userfaultfd_armed(struct vm_area_struct *vma) { return false; diff --git a/mm/huge_memory.c b/mm/huge_memory.c index 6017c73c92a0..0d05abb0cd81 100644 --- a/mm/huge_memory.c +++ b/mm/huge_memory.c @@ -2640,8 +2640,8 @@ bool move_huge_pmd(struct vm_area_struct *vma, unsigned long old_addr, } static void change_non_present_huge_pmd(struct mm_struct *mm, - unsigned long addr, pmd_t *pmd, bool uffd_wp, - bool uffd_wp_resolve) + unsigned long addr, pmd_t *pmd, bool uffd_prot, + bool uffd_prot_resolve) { softleaf_t entry = softleaf_from_pmd(*pmd); const struct folio *folio = softleaf_to_folio(entry); @@ -2667,9 +2667,9 @@ static void change_non_present_huge_pmd(struct mm_struct *mm, newpmd = *pmd; } - if (uffd_wp) + if (uffd_prot) newpmd = pmd_swp_mkuffd(newpmd); - else if (uffd_wp_resolve) + else if (uffd_prot_resolve) newpmd = pmd_swp_clear_uffd(newpmd); if (!pmd_same(*pmd, newpmd)) set_pmd_at(mm, addr, pmd, newpmd); @@ -2690,8 +2690,9 @@ int change_huge_pmd(struct mmu_gather *tlb, struct vm_area_struct *vma, spinlock_t *ptl; pmd_t oldpmd, entry; bool prot_numa = cp_flags & MM_CP_PROT_NUMA; - bool uffd_wp = cp_flags & MM_CP_UFFD_WP; - bool uffd_wp_resolve = cp_flags & MM_CP_UFFD_WP_RESOLVE; + bool uffd_prot = cp_flags & (MM_CP_UFFD_WP | MM_CP_UFFD_RWP); + bool uffd_prot_resolve = cp_flags & + (MM_CP_UFFD_WP_RESOLVE | MM_CP_UFFD_RWP_RESOLVE); int ret = 1; tlb_change_page_size(tlb, HPAGE_PMD_SIZE); @@ -2704,11 +2705,17 @@ int change_huge_pmd(struct mmu_gather *tlb, struct vm_area_struct *vma, return 0; if (thp_migration_supported() && pmd_is_valid_softleaf(*pmd)) { - change_non_present_huge_pmd(mm, addr, pmd, uffd_wp, - uffd_wp_resolve); + change_non_present_huge_pmd(mm, addr, pmd, uffd_prot, + uffd_prot_resolve); goto unlock; } + /* Already in the desired state */ + if (prot_numa && pmd_protnone(*pmd)) + goto unlock; + if ((cp_flags & MM_CP_UFFD_RWP) && pmd_protnone(*pmd) && pmd_uffd(*pmd)) + goto unlock; + if (prot_numa) { /* @@ -2719,9 +2726,6 @@ int change_huge_pmd(struct mmu_gather *tlb, struct vm_area_struct *vma, if (is_huge_zero_pmd(*pmd)) goto unlock; - if (pmd_protnone(*pmd)) - goto unlock; - if (!folio_can_map_prot_numa(pmd_folio(*pmd), vma, vma_is_single_threaded_private(vma))) goto unlock; @@ -2750,9 +2754,9 @@ int change_huge_pmd(struct mmu_gather *tlb, struct vm_area_struct *vma, oldpmd = pmdp_invalidate_ad(vma, addr, pmd); entry = pmd_modify(oldpmd, newprot); - if (uffd_wp) + if (uffd_prot) entry = pmd_mkuffd(entry); - else if (uffd_wp_resolve) + else if (uffd_prot_resolve) /* * Leave the write bit to be handled by PF interrupt * handler, then things like COW could be properly diff --git a/mm/hugetlb.c b/mm/hugetlb.c index d0c81a056ae2..4d75b69d4272 100644 --- a/mm/hugetlb.c +++ b/mm/hugetlb.c @@ -6395,6 +6395,8 @@ long hugetlb_change_protection(struct vm_area_struct *vma, unsigned long last_addr_mask; bool uffd_wp = cp_flags & MM_CP_UFFD_WP; bool uffd_wp_resolve = cp_flags & MM_CP_UFFD_WP_RESOLVE; + bool uffd_rwp = cp_flags & MM_CP_UFFD_RWP; + bool uffd_rwp_resolve = cp_flags & MM_CP_UFFD_RWP_RESOLVE; struct mmu_gather tlb; /* @@ -6420,6 +6422,11 @@ long hugetlb_change_protection(struct vm_area_struct *vma, ptep = hugetlb_walk(vma, address, psize); if (!ptep) { + /* + * uffd_wp installs a pte marker on the unpopulated + * entry; uffd_rwp does not install markers so the + * allocation is unnecessary for it. + */ if (!uffd_wp) { address |= last_addr_mask; continue; @@ -6441,7 +6448,8 @@ long hugetlb_change_protection(struct vm_area_struct *vma, * shouldn't happen at all. Warn about it if it * happened due to some reason. */ - WARN_ON_ONCE(uffd_wp || uffd_wp_resolve); + WARN_ON_ONCE(uffd_wp || uffd_wp_resolve || + uffd_rwp || uffd_rwp_resolve); pages++; spin_unlock(ptl); address |= last_addr_mask; @@ -6475,9 +6483,9 @@ long hugetlb_change_protection(struct vm_area_struct *vma, pages++; } - if (uffd_wp) + if (uffd_wp || uffd_rwp) newpte = pte_swp_mkuffd(newpte); - else if (uffd_wp_resolve) + else if (uffd_wp_resolve || uffd_rwp_resolve) newpte = pte_swp_clear_uffd(newpte); if (!pte_same(pte, newpte)) set_huge_pte_at(mm, address, ptep, newpte, psize); @@ -6488,19 +6496,24 @@ long hugetlb_change_protection(struct vm_area_struct *vma, * pte_marker_uffd_wp()==true implies !poison * because they're mutual exclusive. */ - if (pte_is_uffd_wp_marker(pte) && uffd_wp_resolve) + if (pte_is_uffd_wp_marker(pte) && + (uffd_wp_resolve || uffd_rwp_resolve)) /* Safe to modify directly (non-present->none). */ huge_pte_clear(mm, address, ptep, psize); } else { pte_t old_pte; unsigned int shift = huge_page_shift(hstate_vma(vma)); + /* Already protnone with uffd bit set? Nothing to do. */ + if (uffd_rwp && pte_protnone(pte) && huge_pte_uffd(pte)) + goto next; + old_pte = huge_ptep_modify_prot_start(vma, address, ptep); pte = huge_pte_modify(old_pte, newprot); pte = arch_make_huge_pte(pte, shift, vma->vm_flags); - if (uffd_wp) + if (uffd_wp || uffd_rwp) pte = huge_pte_mkuffd(pte); - else if (uffd_wp_resolve) + else if (uffd_wp_resolve || uffd_rwp_resolve) pte = huge_pte_clear_uffd(pte); huge_ptep_modify_prot_commit(vma, address, ptep, old_pte, pte); pages++; diff --git a/mm/mprotect.c b/mm/mprotect.c index 8340c8b228c6..4a6b35482aee 100644 --- a/mm/mprotect.c +++ b/mm/mprotect.c @@ -214,8 +214,9 @@ static __always_inline void set_write_prot_commit_flush_ptes(struct vm_area_stru static long change_softleaf_pte(struct vm_area_struct *vma, unsigned long addr, pte_t *pte, pte_t oldpte, unsigned long cp_flags) { - const bool uffd_wp = cp_flags & MM_CP_UFFD_WP; - const bool uffd_wp_resolve = cp_flags & MM_CP_UFFD_WP_RESOLVE; + const bool uffd_prot = cp_flags & (MM_CP_UFFD_WP | MM_CP_UFFD_RWP); + const bool uffd_prot_resolve = cp_flags & + (MM_CP_UFFD_WP_RESOLVE | MM_CP_UFFD_RWP_RESOLVE); softleaf_t entry = softleaf_from_pte(oldpte); pte_t newpte; @@ -256,7 +257,7 @@ static long change_softleaf_pte(struct vm_area_struct *vma, * to unprotect it, drop it; the next page * fault will trigger without uffd trapping. */ - if (uffd_wp_resolve) { + if (uffd_prot_resolve) { pte_clear(vma->vm_mm, addr, pte); return 1; } @@ -265,9 +266,9 @@ static long change_softleaf_pte(struct vm_area_struct *vma, newpte = oldpte; } - if (uffd_wp) + if (uffd_prot) newpte = pte_swp_mkuffd(newpte); - else if (uffd_wp_resolve) + else if (uffd_prot_resolve) newpte = pte_swp_clear_uffd(newpte); if (!pte_same(oldpte, newpte)) { @@ -282,16 +283,17 @@ static __always_inline void change_present_ptes(struct mmu_gather *tlb, int nr_ptes, unsigned long end, pgprot_t newprot, struct folio *folio, struct page *page, unsigned long cp_flags) { - const bool uffd_wp_resolve = cp_flags & MM_CP_UFFD_WP_RESOLVE; - const bool uffd_wp = cp_flags & MM_CP_UFFD_WP; + const bool uffd_prot = cp_flags & (MM_CP_UFFD_WP | MM_CP_UFFD_RWP); + const bool uffd_prot_resolve = cp_flags & + (MM_CP_UFFD_WP_RESOLVE | MM_CP_UFFD_RWP_RESOLVE); pte_t ptent, oldpte; oldpte = modify_prot_start_ptes(vma, addr, ptep, nr_ptes); ptent = pte_modify(oldpte, newprot); - if (uffd_wp) + if (uffd_prot) ptent = pte_mkuffd(ptent); - else if (uffd_wp_resolve) + else if (uffd_prot_resolve) ptent = pte_clear_uffd(ptent); /* @@ -325,6 +327,7 @@ static long change_pte_range(struct mmu_gather *tlb, long pages = 0; bool is_private_single_threaded; bool prot_numa = cp_flags & MM_CP_PROT_NUMA; + bool uffd_rwp = cp_flags & MM_CP_UFFD_RWP; bool uffd_wp = cp_flags & MM_CP_UFFD_WP; int nr_ptes; @@ -350,6 +353,14 @@ static long change_pte_range(struct mmu_gather *tlb, /* Already in the desired state. */ if (prot_numa && pte_protnone(oldpte)) continue; + /* + * RWP-protected PTEs carry _PAGE_UFFD as a marker on + * top of PROT_NONE. Skip only entries already in that + * exact state; plain PROT_NONE from mprotect() still needs + * to be promoted so future faults can be distinguished. + */ + if (uffd_rwp && pte_protnone(oldpte) && pte_uffd(oldpte)) + continue; page = vm_normal_page(vma, addr, oldpte); if (page) @@ -358,6 +369,8 @@ static long change_pte_range(struct mmu_gather *tlb, /* * Avoid trapping faults against the zero or KSM * pages. See similar comment in change_huge_pmd. + * Skip this filter for uffd RWP which + * must set protnone regardless of NUMA placement. */ if (prot_numa && !folio_can_map_prot_numa(folio, vma, @@ -667,7 +680,16 @@ long change_protection(struct mmu_gather *tlb, pgprot_t newprot = vma->vm_page_prot; long pages; - BUG_ON((cp_flags & MM_CP_UFFD_WP_ALL) == MM_CP_UFFD_WP_ALL); + /* + * MM_CP_UFFD_{WP,RWP} and _RESOLVE are mutually exclusive within one + * change, and WP and RWP cannot mix. Miswired callers get a warn and + * a no-op; userspace cannot reach this state. + */ + if (WARN_ON_ONCE((cp_flags & MM_CP_UFFD_WP_ALL) == MM_CP_UFFD_WP_ALL || + (cp_flags & MM_CP_UFFD_RWP_ALL) == MM_CP_UFFD_RWP_ALL || + ((cp_flags & MM_CP_UFFD_WP_ALL) && + (cp_flags & MM_CP_UFFD_RWP_ALL)))) + return 0; #ifdef CONFIG_NUMA_BALANCING /* @@ -681,6 +703,10 @@ long change_protection(struct mmu_gather *tlb, WARN_ON_ONCE(cp_flags & MM_CP_PROT_NUMA); #endif + if (IS_ENABLED(CONFIG_ARCH_HAS_PTE_PROTNONE) && + (cp_flags & MM_CP_UFFD_RWP)) + newprot = PAGE_NONE; + if (is_vm_hugetlb_page(vma)) pages = hugetlb_change_protection(vma, start, end, newprot, cp_flags); -- 2.54.0