From nobody Fri Oct 2 08:25:34 2026 Received: from mail-pg1-f198.google.com (mail-pg1-f198.google.com [209.85.215.198]) (using TLSv1.2 with cipher ECDHE-RSA-AES128-GCM-SHA256 (128/128 bits)) (No client certificate requested) by smtp.subspace.kernel.org (Postfix) with ESMTPS id 4A6E1403B18 for ; Mon, 3 Aug 2026 11:39:51 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=209.85.215.198 ARC-Seal: i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1785757192; cv=none; b=ULSkRdNrBwb9ldIaVHZgxsbM6WsNo5jN7uE/cku4u3jAKVgRXr/V+W3B3Ulid77mlooBe5HI3QVj3BpNL3w0s2KzmK0YqsKh9H0oFT7uddzBEta+SiNP2+rZ3JsSQqCeV+Qn6h4jIJwS7DXuhx+19hh+W2OA5xQYJSw+SXvT9jg= ARC-Message-Signature: i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1785757192; c=relaxed/simple; bh=7iCE6EPLEMQ+f44j4KmLuOJ6AsOZQdBDHPzhD2tIc3k=; h=Date:In-Reply-To:Mime-Version:References:Message-ID:Subject:From: To:Cc:Content-Type; b=em+ydXchwg2o05jlrrpqQsoptKKIrfhZb9QJbe5AmsEQUspMSYZ/itML6g9bvN3PqrU4Ff2hKU1bv+7QlJdqm0E43UI9OXbMo1QxvjhVAKIIDkXWf/7GEHXX3Qy6/9cLBj1SvicdHqNcoP6hUdcbtRydKyf8ixQIB2UhrhiyYQE= ARC-Authentication-Results: i=1; smtp.subspace.kernel.org; dmarc=pass (p=reject dis=none) header.from=google.com; spf=pass smtp.mailfrom=flex--praan.bounces.google.com; dkim=pass (2048-bit key) header.d=google.com header.i=@google.com header.b=RWglqRU9; arc=none smtp.client-ip=209.85.215.198 Authentication-Results: smtp.subspace.kernel.org; dmarc=pass (p=reject dis=none) header.from=google.com Authentication-Results: smtp.subspace.kernel.org; spf=pass smtp.mailfrom=flex--praan.bounces.google.com Authentication-Results: smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=google.com header.i=@google.com header.b="RWglqRU9" Received: by mail-pg1-f198.google.com with SMTP id 41be03b00d2f7-ca6bd8a190cso4109520a12.0 for ; Mon, 03 Aug 2026 04:39:51 -0700 (PDT) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=google.com; s=20251104; t=1785757190; x=1786361990; darn=vger.kernel.org; h=content-type:cc:to:from:subject:message-id:references:mime-version :in-reply-to:date:from:to:cc:subject:date:message-id:reply-to :content-type; bh=vv6DECOvSmngHsx3EI9j0R7ut4SHpWl9EkNqXk3pPjk=; b=RWglqRU9EqinXpznbmQcJOiBs+DqTljoSy9zzWTCCPiyJhh0ElrSZr3aioQEyWcsDE ZlIgxi+L6hzdUzcNQRK8hDTCBI+WNXS0oYa298a/P7sEhKP2ll9t0bR7JWBfdZiyfHsN LbOQEvq4BsTaTvvbnahlXEOJ9VWzNtUBD4lvOIr5UNyaxz+BVy60UA/BJ3vrhCbTDQP9 0xEm3J9QqKKJAbKaVlJ0rYxkz31x1kFaIfegg6f6ATlYa5qfgHBoc0tQJ0Hup0YhWtIg aa46a8Ko08ovT3BrLWpkxC4uf8xsBLDxNQ1x70hlSsdiufwMmJzNuUPobPtiM2bpQ5ES aT8w== X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20251104; t=1785757190; x=1786361990; h=content-type:cc:to:from:subject:message-id:references:mime-version :in-reply-to:date:x-gm-message-state:from:to:cc:subject:date :message-id:reply-to:content-type; bh=vv6DECOvSmngHsx3EI9j0R7ut4SHpWl9EkNqXk3pPjk=; b=pUQWL/COpTEwOpG9oE8xxQFHH3ctGZo8g2TpmC/m4qreECDMeRFyMJ/qvXHq7/jHcC Lnpg6ph7HyZXUVq3+G/3zqaFC7axor7+OwqokSAWKkn2lDCo+6ppnN56b4uclOmnP580 ST4Pq6u6vy9WBxwsCskEM90Bqh1TfpUJm/gGA5lV1IAdKb+fIUDpJOlLXsZZN2h58Ohy 3Rx77R4GRlN2LrJVqyWpUci/DndNWUikX+8JD3jOeTgpV8yGJwQ2wtdprMVOmuk9tl45 8FrNoX+cR0D0DJ/TLWm+46DTTzX88JW/T4lk2tOtC9OWp/aHhaNulFzRlv5kR9j6wzad 4p3Q== X-Forwarded-Encrypted: i=1; AHgh+RriCKH6fGpCjTcAgk1LjperFbT+/1eO7SyBoFzezzsXLqxLdAbZGpDJCXj4IZp7MttS4EJPXck2OT0e5/Y=@vger.kernel.org X-Gm-Message-State: AOJu0Yyvf7Z3DjRd9VIfnoQ+yNJ65eepYqYU+ls4FWmh/k5NakwYD4CF ZkONuJIIev7MnwwZpzE1F6s9Qy8GBOReLQL+79g6r3Xy7HZIR0o/PieaewTcUSdJUrgyuKBc/G/ +gw== X-Received: from pgvi9.prod.google.com ([2002:a65:61a9:0:b0:c9a:c533:8329]) (user=praan job=prod-delivery.src-stubby-dispatcher) by 2002:a05:6a21:e58d:b0:3bf:e3d6:ab5a with SMTP id adf61e73a8af0-3c92a8f327cmr10771333637.52.1785757190359; Mon, 03 Aug 2026 04:39:50 -0700 (PDT) Date: Mon, 3 Aug 2026 11:39:42 +0000 In-Reply-To: <20260803113944.3694290-1-praan@google.com> Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: Mime-Version: 1.0 References: <20260803113944.3694290-1-praan@google.com> X-Mailer: git-send-email 2.55.0.508.g3f0d502094-goog Message-ID: <20260803113944.3694290-2-praan@google.com> Subject: [PATCH v4 1/2] kho: Introduce a helper to init high order pages From: Pranjal Shrivastava To: Mike Rapoport , Pasha Tatashin , Pratyush Yadav Cc: Alexander Graf , Samiullah Khawaja , David Matlack , kexec@lists.infradead.org, linux-mm@kvack.org, linux-kernel@vger.kernel.org, Pranjal Shrivastava Content-Transfer-Encoding: quoted-printable Content-Type: text/plain; charset="utf-8" The current KHO restoration logic assumes all multi-page blocks are split into independent 4KB pages. Break out a helper to prepare for supporting high-order non-compound pages. Extract kho_init_high_order_page() to handle the refcount pattern where only the head page is refcounted. Use the helper for folio restoration that requires a similar refcount logic. Reviewed-by: Samiullah Khawaja Signed-off-by: Pranjal Shrivastava --- kernel/liveupdate/kexec_handover.c | 29 +++++++++++++++++++---------- 1 file changed, 19 insertions(+), 10 deletions(-) diff --git a/kernel/liveupdate/kexec_handover.c b/kernel/liveupdate/kexec_h= andover.c index 4834a809985a..e836efd98795 100644 --- a/kernel/liveupdate/kexec_handover.c +++ b/kernel/liveupdate/kexec_handover.c @@ -357,6 +357,24 @@ int kho_radix_walk_tree(struct kho_radix_tree *tree, } EXPORT_SYMBOL_GPL(kho_radix_walk_tree); =20 +/* For physically contiguous pages. */ +static void kho_init_high_order_page(struct page *page, unsigned int order) +{ + unsigned long nr_pages =3D (1UL << order); + + /* Head page gets refcount of 1. */ + set_page_count(page, 1); + /* Clear head page's codetag to avoid accounting mismatch. */ + clear_page_tag_ref(page); + + /* For high-order blocks, tail pages get a page count of zero. */ + for (unsigned long i =3D 1; i < nr_pages; i++) { + set_page_count(page + i, 0); + /* Clear each page's codetag to avoid accounting mismatch. */ + clear_page_tag_ref(page + i); + } +} + /* For physically contiguous 0-order pages. */ static void kho_init_pages(struct page *page, unsigned long nr_pages) { @@ -369,16 +387,7 @@ static void kho_init_pages(struct page *page, unsigned= long nr_pages) =20 static void kho_init_folio(struct page *page, unsigned int order) { - unsigned long nr_pages =3D (1 << order); - - /* Head page gets refcount of 1. */ - set_page_count(page, 1); - /* Clear head page's codetag to avoid accounting mismatch. */ - clear_page_tag_ref(page); - - /* For higher order folios, tail pages get a page count of zero. */ - for (unsigned long i =3D 1; i < nr_pages; i++) - set_page_count(page + i, 0); + kho_init_high_order_page(page, order); =20 if (order > 0) prep_compound_page(page, order); --=20 2.55.0.508.g3f0d502094-goog From nobody Fri Oct 2 08:25:34 2026 Received: from mail-pl1-f198.google.com (mail-pl1-f198.google.com [209.85.214.198]) (using TLSv1.2 with cipher ECDHE-RSA-AES128-GCM-SHA256 (128/128 bits)) (No client certificate requested) by smtp.subspace.kernel.org (Postfix) with ESMTPS id 841E6403E81 for ; 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Mon, 03 Aug 2026 04:39:52 -0700 (PDT) Date: Mon, 3 Aug 2026 11:39:43 +0000 In-Reply-To: <20260803113944.3694290-1-praan@google.com> Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: Mime-Version: 1.0 References: <20260803113944.3694290-1-praan@google.com> X-Mailer: git-send-email 2.55.0.508.g3f0d502094-goog Message-ID: <20260803113944.3694290-3-praan@google.com> Subject: [PATCH v4 2/2] kho: Introduce preserve/restore APIs for high-order pages From: Pranjal Shrivastava To: Mike Rapoport , Pasha Tatashin , Pratyush Yadav Cc: Alexander Graf , Samiullah Khawaja , David Matlack , kexec@lists.infradead.org, linux-mm@kvack.org, linux-kernel@vger.kernel.org, Pranjal Shrivastava Content-Transfer-Encoding: quoted-printable Content-Type: text/plain; charset="utf-8" The current KHO page preservation APIs (e.g. kho_preserve_pages) assume that multi-page blocks are split into independent 4KB pages during restoration. This is incompatible with high-order non-compound pages, such as DMA buffers, which must be restored with tail pages having a zero reference count. Introduce explicit preserve and restore APIs for high-order pages, which preserve and restore a high-order page block as a single unit, applying a refcount of 1 to the head page while leaving tail pages at 0. Rename the existing internal helper to __kho_restore_page() and consolidate the common restoration code into it. Signed-off-by: Pranjal Shrivastava --- include/linux/kexec_handover.h | 10 +++ kernel/liveupdate/kexec_handover.c | 98 ++++++++++++++++++++++++++---- 2 files changed, 96 insertions(+), 12 deletions(-) diff --git a/include/linux/kexec_handover.h b/include/linux/kexec_handover.h index 8968c56d2d73..6e2c75b16209 100644 --- a/include/linux/kexec_handover.h +++ b/include/linux/kexec_handover.h @@ -22,6 +22,8 @@ bool is_kho_boot(void); =20 int kho_preserve_folio(struct folio *folio); void kho_unpreserve_folio(struct folio *folio); +int kho_preserve_page(struct page *page, unsigned int order); +void kho_unpreserve_page(struct page *page, unsigned int order); int kho_preserve_pages(struct page *page, unsigned long nr_pages); void kho_unpreserve_pages(struct page *page, unsigned long nr_pages); int kho_preserve_vmalloc(void *ptr, struct kho_vmalloc *preservation); @@ -30,6 +32,7 @@ void *kho_alloc_preserve(size_t size); void kho_unpreserve_free(void *mem); void kho_restore_free(void *mem); struct folio *kho_restore_folio(phys_addr_t phys); +struct page *kho_restore_page(phys_addr_t phys); struct page *kho_restore_pages(phys_addr_t phys, unsigned long nr_pages); void *kho_restore_vmalloc(const struct kho_vmalloc *preservation); int kho_add_subtree(const char *name, void *blob, size_t size); @@ -65,6 +68,13 @@ static inline int kho_preserve_pages(struct page *page, = unsigned int nr_pages) =20 static inline void kho_unpreserve_pages(struct page *page, unsigned int nr= _pages) { } =20 +static inline int kho_preserve_page(struct page *page, unsigned int order) +{ + return -EOPNOTSUPP; +} + +static inline void kho_unpreserve_page(struct page *page, unsigned int ord= er) { } + static inline int kho_preserve_vmalloc(void *ptr, struct kho_vmalloc *preservation) { diff --git a/kernel/liveupdate/kexec_handover.c b/kernel/liveupdate/kexec_h= andover.c index e836efd98795..dd41d324c213 100644 --- a/kernel/liveupdate/kexec_handover.c +++ b/kernel/liveupdate/kexec_handover.c @@ -393,10 +393,9 @@ static void kho_init_folio(struct page *page, unsigned= int order) prep_compound_page(page, order); } =20 -static struct page *kho_restore_page(phys_addr_t phys, bool is_folio) +static struct page *__kho_restore_page(phys_addr_t phys, unsigned int *ord= er) { struct page *page =3D pfn_to_online_page(PHYS_PFN(phys)); - unsigned long nr_pages; union kho_page_info info; =20 if (!page) @@ -410,17 +409,14 @@ static struct page *kho_restore_page(phys_addr_t phys= , bool is_folio) */ if (WARN_ON_ONCE(info.magic !=3D KHO_PAGE_MAGIC)) return NULL; - nr_pages =3D (1 << info.order); =20 /* Clear private to make sure later restores on this page error out. */ page->private =3D 0; + if (order) + *order =3D info.order; =20 - if (is_folio) - kho_init_folio(page, info.order); - else - kho_init_pages(page, nr_pages); + adjust_managed_page_count(page, 1UL << info.order); =20 - adjust_managed_page_count(page, nr_pages); return page; } =20 @@ -432,12 +428,41 @@ static struct page *kho_restore_page(phys_addr_t phys= , bool is_folio) */ struct folio *kho_restore_folio(phys_addr_t phys) { - struct page *page =3D kho_restore_page(phys, true); + unsigned int order; + struct page *page =3D __kho_restore_page(phys, &order); + + if (!page) + return NULL; + + kho_init_folio(page, order); =20 - return page ? page_folio(page) : NULL; + return page_folio(page); } EXPORT_SYMBOL_GPL(kho_restore_folio); =20 +/** + * kho_restore_page - restore a high-order page block. + * @phys: physical address of the first page. + * + * Restore a high-order page block that was preserved with + * kho_preserve_page(). + * + * Return: the head page on success, NULL on failure. + */ +struct page *kho_restore_page(phys_addr_t phys) +{ + unsigned int order; + struct page *page =3D __kho_restore_page(phys, &order); + + if (!page) + return NULL; + + kho_init_high_order_page(page, order); + + return page; +} +EXPORT_SYMBOL_GPL(kho_restore_page); + /** * kho_restore_pages - restore list of contiguous order 0 pages. * @phys: physical address of the first page. @@ -457,10 +482,13 @@ struct page *kho_restore_pages(phys_addr_t phys, unsi= gned long nr_pages) while (pfn < end_pfn) { const unsigned int order =3D min(count_trailing_zeros(pfn), ilog2(end_pfn - pfn)); - struct page *page =3D kho_restore_page(PFN_PHYS(pfn), false); + unsigned int info_order; + struct page *page =3D __kho_restore_page(PFN_PHYS(pfn), &info_order); =20 if (!page) return NULL; + + kho_init_pages(page, 1UL << info_order); pfn +=3D 1 << order; } =20 @@ -890,6 +918,51 @@ void kho_unpreserve_folio(struct folio *folio) } EXPORT_SYMBOL_GPL(kho_unpreserve_folio); =20 +/** + * kho_preserve_page - preserve a high-order page block. + * @page: head page of the block. + * @order: order of the allocation. + * + * Instructs KHO to preserve a high-order contiguous allocation (like a DMA + * buffer) as a single unit. It must be restored using kho_restore_page() = to + * ensure the tail pages are correctly initialized with a zero refcount. + * + * If a driver needs to split a block that has been preserved with this + * function, it must first unpreserve the block using kho_unpreserve_page(= ), + * perform the split, and then re-preserve the individual pages using + * kho_preserve_pages(). + * + * Return: 0 on success, error code on failure + */ +int kho_preserve_page(struct page *page, unsigned int order) +{ + struct kho_radix_tree *tree =3D &kho_out.radix_tree; + const unsigned long pfn =3D page_to_pfn(page); + + if (WARN_ON(kho_scratch_overlap(pfn << PAGE_SHIFT, PAGE_SIZE << order))) + return -EINVAL; + + return kho_radix_add_page(tree, pfn, order); +} +EXPORT_SYMBOL_GPL(kho_preserve_page); + +/** + * kho_unpreserve_page - unpreserve a high-order page block. + * @page: head page of the block. + * @order: order of the allocation. + * + * Instructs KHO to unpreserve a high-order block that was preserved by + * kho_preserve_page() before. + */ +void kho_unpreserve_page(struct page *page, unsigned int order) +{ + struct kho_radix_tree *tree =3D &kho_out.radix_tree; + const unsigned long pfn =3D page_to_pfn(page); + + kho_radix_del_page(tree, pfn, order); +} +EXPORT_SYMBOL_GPL(kho_unpreserve_page); + static unsigned int __kho_preserve_pages_order(unsigned long start_pfn, unsigned long end_pfn) { @@ -927,7 +1000,8 @@ static void __kho_unpreserve(struct kho_radix_tree *tr= ee, * @nr_pages: number of pages. * * Preserve a contiguous list of order 0 pages. Must be restored using - * kho_restore_pages() to ensure the pages are restored properly as order = 0. + * kho_restore_pages() to ensure the pages are restored properly as order 0 + * with each page having a reference count of 1 (split). * * Return: 0 on success, error code on failure */ --=20 2.55.0.508.g3f0d502094-goog