From mboxrd@z Thu Jan 1 00:00:00 1970 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 ; Mon, 3 Aug 2026 11:39:53 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=209.85.214.198 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1785757195; cv=none; b=SP6HtIttaZchJ8rA+iDOletNKydIyHgKclnamHeXKykLczFwlBBUQI8TY/oSYCU4qlYJpYR/1tB5VpCB2fsDHH6QsnQypHBxFXcD4RxBTjeXU6uyD6yLAbAXdL0dRCfgHmD3s0A566F9LON20MWz1BUXkpLA69jDQ/ct67XHRdw= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1785757195; c=relaxed/simple; bh=hSC3TQcWS9SG8uKOllmXTGpzywg13xb/hJ5qKom56nY=; h=Date:In-Reply-To:Mime-Version:References:Message-ID:Subject:From: To:Cc:Content-Type; b=pesRgsyYLAXYhGSq/I+ALV8FZwS15wNqjiPuBsSMY0aZMBWTMuhIn9YFPW7CTT6SUkNNuCPLzwBSMo7MVms14b5jfpud6aCoE+H3ntlBs4CMvFQgOtk+cMrN9GxAgnav+8L6hmuuqOeQc80oxMlpsH3fRAlViZqjWsR/AY0eSP8= 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=ekDOeG3M; arc=none smtp.client-ip=209.85.214.198 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="ekDOeG3M" Received: by mail-pl1-f198.google.com with SMTP id d9443c01a7336-2cfbf3e4a63so96191045ad.0 for ; Mon, 03 Aug 2026 04:39:53 -0700 (PDT) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=google.com; s=20251104; t=1785757193; x=1786361993; 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=3WS6p2C4BmwdiRsncUpnqm0L7Z6/0c6U1cXqlGa6Rj0=; b=ekDOeG3M5SfwKwxUA7exurOJ75+zZ+F6YGrOdL5orWFRzzs1vcS04Bc2fjGHBSNyFG vTxrNRZTZUsAiq0KDPr3xNXGuIq2gq3iBH+Xky/umfLGiCHHvsahptYFI0+soBLgxWxa oWSK5QAcSbbZu0Q3JiD7P3uYmNcxxsjM5AHCSGGbHhQbNMh4lwMGnrmj5SVtWkdm2DYm qfPxt/vKIjf0oSFsA/XySqp+L4wFTl5fMLJonxh9S21jz17ltoD6PuRctekdyWUJ81m3 lgdBMRHP+xpvmYxfRcveWYwv7ijQhe2nz+JToQGciITlbcvaAeoWQgEoCy+fPk+XFGGX 4dew== X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20251104; t=1785757193; x=1786361993; 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=3WS6p2C4BmwdiRsncUpnqm0L7Z6/0c6U1cXqlGa6Rj0=; b=jWIwYnyexZcOOYtFQ/h6LdQOD0/+OXXVGF/kc0JuhBeJ9rRYwJ/kMe1Fhe+qfijaJA rWBKYJ8x9vRfJ6il49xkFfVkV8QxvMDfB9znoVhAqXS5D8lYcZTf8iXz/ybEML4kkG3P 9eho5G6q4Pc0TWQJq/P69czSgOcESKLk8UfzpEK+1IF6OW3BNpt4dPQSOxQB2fS5l5OT gN3J2SaYY4M+B3+NT13gi0JDuUMlnHxmeycys119zkWB8TNuqGLfrcyaG8ngRzWT1xd0 vRCw5eYzKwJLvSk6zOeaSMPyZEH7c0ZFCpRqKh0GraUkawxDKTjPxy3J7l+Aj0J7WErb jA3A== X-Forwarded-Encrypted: i=1; AHgh+RoaUnl386rFuuxMM0nVfe+SjsOC9HI5Dv5ov7p6AdhbI1c6JtsSAuCief/z24RLFS+uNJMsm9I2F/eDC68=@vger.kernel.org X-Gm-Message-State: AOJu0YwaBBSdHtoqNRK13PL0jzNDVqOpvkxzI7X7D9gOzHX+sLybfn1M KX8OzUG7UtN4dwpVbICO+DbXlt7y7+POANg8T2O/SddK1sc9DZ/MnBUj0EpAYlVd1tkGpxVafLc YHA== X-Received: from pgno7.prod.google.com ([2002:a63:7e47:0:b0:ca2:10cf:5d95]) (user=praan job=prod-delivery.src-stubby-dispatcher) by 2002:a05:6a21:710e:b0:3c3:6528:c87 with SMTP id adf61e73a8af0-3c92a519c67mr10067044637.1.1785757192568; 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-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); 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) static inline void kho_unpreserve_pages(struct page *page, unsigned int nr_pages) { } +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 order) { } + static inline int kho_preserve_vmalloc(void *ptr, struct kho_vmalloc *preservation) { diff --git a/kernel/liveupdate/kexec_handover.c b/kernel/liveupdate/kexec_handover.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); } -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 *order) { struct page *page = pfn_to_online_page(PHYS_PFN(phys)); - unsigned long nr_pages; union kho_page_info info; 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 != KHO_PAGE_MAGIC)) return NULL; - nr_pages = (1 << info.order); /* Clear private to make sure later restores on this page error out. */ page->private = 0; + if (order) + *order = info.order; - if (is_folio) - kho_init_folio(page, info.order); - else - kho_init_pages(page, nr_pages); + adjust_managed_page_count(page, 1UL << info.order); - adjust_managed_page_count(page, nr_pages); return page; } @@ -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 = kho_restore_page(phys, true); + unsigned int order; + struct page *page = __kho_restore_page(phys, &order); + + if (!page) + return NULL; + + kho_init_folio(page, order); - return page ? page_folio(page) : NULL; + return page_folio(page); } EXPORT_SYMBOL_GPL(kho_restore_folio); +/** + * 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 = __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, unsigned long nr_pages) while (pfn < end_pfn) { const unsigned int order = min(count_trailing_zeros(pfn), ilog2(end_pfn - pfn)); - struct page *page = kho_restore_page(PFN_PHYS(pfn), false); + unsigned int info_order; + struct page *page = __kho_restore_page(PFN_PHYS(pfn), &info_order); if (!page) return NULL; + + kho_init_pages(page, 1UL << info_order); pfn += 1 << order; } @@ -890,6 +918,51 @@ void kho_unpreserve_folio(struct folio *folio) } EXPORT_SYMBOL_GPL(kho_unpreserve_folio); +/** + * 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 = &kho_out.radix_tree; + const unsigned long pfn = 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 = &kho_out.radix_tree; + const unsigned long pfn = 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 *tree, * @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 */ -- 2.55.0.508.g3f0d502094-goog