From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org Received: from kanga.kvack.org (kanga.kvack.org [205.233.56.17]) (using TLSv1 with cipher DHE-RSA-AES256-SHA (256/256 bits)) (No client certificate requested) by smtp.lore.kernel.org (Postfix) with ESMTPS id DDA56C61DE2 for ; Mon, 31 Aug 2026 00:25:47 +0000 (UTC) Received: by kanga.kvack.org (Postfix) id DC4B16B0092; Sun, 30 Aug 2026 20:25:24 -0400 (EDT) Received: by kanga.kvack.org (Postfix, from userid 40) id D4E1D6B0095; Sun, 30 Aug 2026 20:25:24 -0400 (EDT) X-Delivered-To: int-list-linux-mm@kvack.org Received: by kanga.kvack.org (Postfix, from userid 63042) id B51976B0092; Sun, 30 Aug 2026 20:25:24 -0400 (EDT) X-Delivered-To: linux-mm@kvack.org Received: from relay.hostedemail.com (smtprelay0011.hostedemail.com [216.40.44.11]) by kanga.kvack.org (Postfix) with ESMTP id 8EAEE6B0096 for ; Sun, 30 Aug 2026 20:25:24 -0400 (EDT) Received: from smtpin29.hostedemail.com (lb01a-stub [10.200.18.249]) by unirelay05.hostedemail.com (Postfix) with ESMTP id DB099403B0 for ; Mon, 31 Aug 2026 00:25:23 +0000 (UTC) X-FDA: 85159670526.29.2BF0C76 Received: from sea.source.kernel.org (sea.source.kernel.org [172.234.252.31]) by imf28.hostedemail.com (Postfix) with ESMTP id E902EC0008 for ; Mon, 31 Aug 2026 00:25:21 +0000 (UTC) Authentication-Results: imf28.hostedemail.com; dkim=pass header.d=kernel.org header.s=k20201202 header.b=dnvaMDDb; spf=pass (imf28.hostedemail.com: domain of devnull+ackerleytng.google.com@kernel.org designates 172.234.252.31 as permitted sender) smtp.mailfrom=devnull+ackerleytng.google.com@kernel.org; dmarc=pass (policy=quarantine) header.from=kernel.org ARC-Seal: i=1; a=rsa-sha256; d=hostedemail.com; s=arc-20220608; cv=none; t=1788135922; b=Lg3upXopCBZUwcpCxI6sARkqXT0AiDclHOUp6hiAz4YRZmPqmwyJYZgeKDqLA4dPv2P0hS juTLHkM36iiOpl1TqVoD9uZnkSMpcvydf9o8qmUzz3t8FLgENTqpUTLjVRxi9GVYA48HpI THaTu47vQWCUoAU1SuGn6A+5s8eevfY= ARC-Authentication-Results: i=1; imf28.hostedemail.com; dkim=pass header.d=kernel.org header.s=k20201202 header.b=dnvaMDDb; spf=pass (imf28.hostedemail.com: domain of devnull+ackerleytng.google.com@kernel.org designates 172.234.252.31 as permitted sender) smtp.mailfrom=devnull+ackerleytng.google.com@kernel.org; dmarc=pass (policy=quarantine) header.from=kernel.org ARC-Message-Signature: i=1; a=rsa-sha256; c=relaxed/relaxed; d=hostedemail.com; s=arc-20220608; t=1788135922; h=from:from:sender:reply-to:reply-to:subject:subject:date:date: message-id:message-id:to:to:cc:cc:mime-version:mime-version: content-type:content-type: content-transfer-encoding:content-transfer-encoding: in-reply-to:in-reply-to:references:references:dkim-signature; bh=fl4PgRDHs5ir+9hmU2jjg3/SXhxGhBhrB27GFcAgqJA=; b=mD3f/5BEc8xqOOKiUZOwfL4wX3yjo/Hl9zsOSardRUZTQe8Gv/wwUEUDmnv7yVpj0bWBLz eKsdUUfYE0g4vwShi3BqZ20OY8exNL7EFrfycMSVsSHqCbpgvqY31AvE2hMTwV9D08RhKF aRUu2AsvNZWYR5VxzX2F0jZgO5AiFEM= Received: from smtp.kernel.org (transwarp.subspace.kernel.org [100.75.92.58]) by sea.source.kernel.org (Postfix) with ESMTP id 1CA6643FE4; Mon, 31 Aug 2026 00:25:20 +0000 (UTC) Received: by smtp.kernel.org (Postfix) with ESMTPS id B879FC4AF19; Mon, 31 Aug 2026 00:25:19 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=k20201202; t=1788135919; bh=cQsJwwAdgl6as/zP1eyJ1SShuRQR+8U5D8In8m4y84k=; h=From:Date:Subject:References:In-Reply-To:To:Cc:Reply-To:From; b=dnvaMDDbpagrivQOgB3jNyFMdVBElgF6q1YNlCao3e5zSBVySwrG9lIVWkyJ1prpP uiGn/0IaXbkz7rH8mLVUO+aC89ObX/XghF/G5QKfQxDQRNSYO9AbZ50mspMf8A1liM X5BYI8Ic9GvJ5ZP14E3nZgBVJFcPLBYn4B4r2RPrUUJziAP8Ro3iOpI9qutPHMj7j1 3+wUS263OTV+te4AR5K3+cP0bqK2ujOA23/go/oCKBruYmdtBF/OIE7M9rYEyxxVV7 geLWU1l4vzwilqI1C9OLoXpcxvxgYRb8vjal51LKMcCzFome99f+s+u5yYRjG5+PUt Izjx4zw0e9ZlA== Received: from aws-us-west-2-korg-lkml-1.web.codeaurora.org (localhost.localdomain [127.0.0.1]) by smtp.lore.kernel.org (Postfix) with ESMTP id A1BB4C61DE4; Mon, 31 Aug 2026 00:25:19 +0000 (UTC) From: Ackerley Tng via B4 Relay Date: Sun, 30 Aug 2026 17:25:04 -0700 Subject: [PATCH v12 03/45] KVM: guest_memfd: Introduce per-gmem attributes, use to guard user mappings MIME-Version: 1.0 Content-Type: text/plain; charset="utf-8" Content-Transfer-Encoding: 7bit Message-Id: <20260830-gmem-inplace-conversion-v12-3-85e5fd25252a@google.com> References: <20260830-gmem-inplace-conversion-v12-0-85e5fd25252a@google.com> In-Reply-To: <20260830-gmem-inplace-conversion-v12-0-85e5fd25252a@google.com> To: aik@amd.com, andrew.jones@linux.dev, binbin.wu@linux.intel.com, brauner@kernel.org, chao.p.peng@linux.intel.com, david@kernel.org, jmattson@google.com, jthoughton@google.com, michael.roth@amd.com, oupton@kernel.org, pankaj.gupta@amd.com, qperret@google.com, rick.p.edgecombe@intel.com, rientjes@google.com, shivankg@amd.com, steven.price@arm.com, willy@infradead.org, wyihan@google.com, yan.y.zhao@intel.com, forkloop@google.com, pratyush@kernel.org, suzuki.poulose@arm.com, aneesh.kumar@kernel.org, liam@infradead.org, Paolo Bonzini , Sean Christopherson , Thomas Gleixner , Ingo Molnar , Borislav Petkov , Dave Hansen , x86@kernel.org, "H. Peter Anvin" , Steven Rostedt , Masami Hiramatsu , Mathieu Desnoyers , Jonathan Corbet , Shuah Khan , Shuah Khan , Vishal Annapurve , Andrew Morton , Chris Li , Kairui Song , Kemeng Shi , Nhat Pham , Barry Song , Axel Rasmussen , Yuanchu Xie , Wei Xu , Youngjun Park , Qi Zheng , Shakeel Butt , Kiryl Shutsemau , Baoquan He , Jason Gunthorpe , John Hubbard , Peter Xu , tarunsahu@google.com, Randy Dunlap , Lorenzo Stoakes , Vlastimil Babka , Mike Rapoport , Suren Baghdasaryan , Michal Hocko , Jason Gunthorpe , Fuad Tabba , Vlastimil Babka , Baoquan He Cc: kvm@vger.kernel.org, linux-kernel@vger.kernel.org, linux-trace-kernel@vger.kernel.org, linux-doc@vger.kernel.org, linux-kselftest@vger.kernel.org, linux-mm@kvack.org, linux-coco@lists.linux.dev, Ackerley Tng , Xiaoyao Li X-Mailer: b4 0.14.3 X-Developer-Signature: v=1; a=ed25519-sha256; t=1788135915; l=8901; i=ackerleytng@google.com; s=20260225; h=from:subject:message-id; bh=H+Foxo2jkk0EvS1xizl1rXzAIb0v1aN2W7mi7/WZF/o=; b=iafaIhiBr5nL66w1QN+aqiUa27rAU5GRN8Uxc7LJ6x2LcNgjQzD7Z0SFlKt1Y1NG1gHPxQd9S /In+BlOkxOfAGXNJ1fFsWiBjwYZqY+KMiA+gMkTPNmnocnV3X0byT4O X-Developer-Key: i=ackerleytng@google.com; a=ed25519; pk=sAZDYXdm6Iz8FHitpHeFlCMXwabodTm7p8/3/8xUxuU= X-Endpoint-Received: by B4 Relay for ackerleytng@google.com/20260225 with auth_id=649 X-Original-From: Ackerley Tng Reply-To: ackerleytng@google.com X-Rspam-User: X-Rspamd-Server: rspam10 X-Rspamd-Queue-Id: E902EC0008 X-Stat-Signature: y91cqpdg41qc3tr6ddzc48wn7t83ndah X-HE-Tag: 1788135921-484277 X-HE-Meta: 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 T1wNY3ye 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 Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: List-Subscribe: List-Unsubscribe: From: Sean Christopherson Start plumbing in guest_memfd support for in-place private<=>shared conversions by tracking attributes via a maple tree. KVM currently tracks private vs. shared attributes on a per-VM basis, which made sense when a guest_memfd _only_ supported private memory, but tracking per-VM simply can't work for in-place conversions as the shared/private status of a given page needs to be per-gmem_inode, not per-VM. Use the filemap invalidation lock to protect the maple tree, as taking the lock for read when faulting in memory (for userspace or the guest) isn't expected to result in meaningful contention, and using a separate lock would add significant complexity (avoiding deadlock is quite difficult). In kvm_gmem_get_pfn(), drop the folio refcount before releasing filemap_invalidate_lock(). This ensures that a competing conversion request from userspace (to be added in a later patch), which also takes the filemap_invalidate_lock(), will never see an elevated refcount due to kvm_gmem_get_pfn(). Co-developed-by: Vishal Annapurve Signed-off-by: Vishal Annapurve Co-developed-by: Fuad Tabba Signed-off-by: Fuad Tabba Signed-off-by: Sean Christopherson Tested-by: Shivank Garg Reviewed-by: Xiaoyao Li Reviewed-by: Binbin Wu Co-developed-by: Ackerley Tng Signed-off-by: Ackerley Tng --- virt/kvm/guest_memfd.c | 136 ++++++++++++++++++++++++++++++++++++++++++------- 1 file changed, 119 insertions(+), 17 deletions(-) diff --git a/virt/kvm/guest_memfd.c b/virt/kvm/guest_memfd.c index 69612bf146be1..e32ac2c28cbef 100644 --- a/virt/kvm/guest_memfd.c +++ b/virt/kvm/guest_memfd.c @@ -4,6 +4,7 @@ #include #include #include +#include #include #include #include @@ -34,6 +35,13 @@ struct gmem_inode { struct list_head gmem_file_list; u64 flags; + /* + * Every index in this inode, whether memory is populated or + * not, is tracked in attributes. The entire range of indices, + * corresponding to the size of this inode, is represented in + * this maple tree. + */ + struct maple_tree attributes; }; static __always_inline struct gmem_inode *GMEM_I(struct inode *inode) @@ -61,9 +69,28 @@ static pgoff_t kvm_gmem_get_index(struct kvm_memory_slot *slot, gfn_t gfn) return gfn - slot->base_gfn + slot->gmem.pgoff; } +static u64 kvm_gmem_get_default_attributes(struct inode *inode) +{ + bool init_shared = GMEM_I(inode)->flags & GUEST_MEMFD_FLAG_INIT_SHARED; + + return init_shared ? 0 : KVM_MEMORY_ATTRIBUTE_PRIVATE; +} + +static u64 kvm_gmem_get_attributes(struct inode *inode, void *entry) +{ + if (WARN_ON_ONCE(!entry)) + return kvm_gmem_get_default_attributes(inode); + + return xa_to_value(entry); +} + static bool kvm_gmem_is_private_mem(struct inode *inode, pgoff_t index) { - return !(GMEM_I(inode)->flags & GUEST_MEMFD_FLAG_INIT_SHARED); + struct maple_tree *mt = &GMEM_I(inode)->attributes; + void *entry = mtree_load(mt, index); + + return kvm_gmem_get_attributes(inode, entry) & + KVM_MEMORY_ATTRIBUTE_PRIVATE; } static bool kvm_gmem_is_shared_mem(struct inode *inode, pgoff_t index) @@ -364,10 +391,13 @@ static vm_fault_t kvm_gmem_fault_user_mapping(struct vm_fault *vmf) if (((loff_t)vmf->pgoff << PAGE_SHIFT) >= i_size_read(inode)) return VM_FAULT_SIGBUS; - if (!kvm_gmem_is_shared_mem(inode, vmf->pgoff)) - return VM_FAULT_SIGBUS; + filemap_invalidate_lock_shared(inode->i_mapping); + if (kvm_gmem_is_shared_mem(inode, vmf->pgoff)) + folio = kvm_gmem_get_folio(inode, vmf->pgoff); + else + folio = ERR_PTR(-EACCES); + filemap_invalidate_unlock_shared(inode->i_mapping); - folio = kvm_gmem_get_folio(inode, vmf->pgoff); if (IS_ERR(folio)) { if (PTR_ERR(folio) == -EAGAIN) return VM_FAULT_RETRY; @@ -520,6 +550,51 @@ bool __weak kvm_arch_supports_gmem_init_shared(struct kvm *kvm) return true; } +static int kvm_gmem_init_inode(struct inode *inode, loff_t size, u64 flags) +{ + struct gmem_inode *gi = GMEM_I(inode); + MA_STATE(mas, &gi->attributes, 0, (size >> PAGE_SHIFT) - 1); + u64 attrs; + int r; + + inode->i_op = &kvm_gmem_iops; + inode->i_mapping->a_ops = &kvm_gmem_aops; + inode->i_mode |= S_IFREG; + inode->i_size = size; + mapping_set_gfp_mask(inode->i_mapping, GFP_HIGHUSER); + + /* + * guest_memfd memory is neither migratable nor swappable: set + * inaccessible to gate off both. + */ + mapping_set_inaccessible(inode->i_mapping); + WARN_ON_ONCE(!mapping_unevictable(inode->i_mapping)); + + gi->flags = flags; + + mt_set_external_lock(&gi->attributes, + &inode->i_mapping->invalidate_lock); + + /* + * Store default attributes for the entire gmem instance. Ensuring every + * index is represented in the maple tree at all times simplifies the + * conversion and merging logic. + */ + attrs = kvm_gmem_get_default_attributes(inode); + + /* + * Acquire the invalidation lock purely to make lockdep happy. The + * maple tree library expects all stores to be protected via the lock, + * and the library can't know when the tree is reachable only by the + * caller, as is the case here. + */ + filemap_invalidate_lock(inode->i_mapping); + r = mas_store_gfp(&mas, xa_mk_value(attrs), GFP_KERNEL); + filemap_invalidate_unlock(inode->i_mapping); + + return r; +} + static int __kvm_gmem_create(struct kvm *kvm, loff_t size, u64 flags) { static const char *name = "[kvm-gmem]"; @@ -550,16 +625,9 @@ static int __kvm_gmem_create(struct kvm *kvm, loff_t size, u64 flags) goto err_fops; } - inode->i_op = &kvm_gmem_iops; - inode->i_mapping->a_ops = &kvm_gmem_aops; - inode->i_mode |= S_IFREG; - inode->i_size = size; - mapping_set_gfp_mask(inode->i_mapping, GFP_HIGHUSER); - mapping_set_inaccessible(inode->i_mapping); - /* Unmovable mappings are supposed to be marked unevictable as well. */ - WARN_ON_ONCE(!mapping_unevictable(inode->i_mapping)); - - GMEM_I(inode)->flags = flags; + err = kvm_gmem_init_inode(inode, size, flags); + if (err) + goto err_inode; file = alloc_file_pseudo(inode, kvm_gmem_mnt, name, O_RDWR, &kvm_gmem_fops); if (IS_ERR(file)) { @@ -763,9 +831,13 @@ int kvm_gmem_get_pfn(struct kvm *kvm, struct kvm_memory_slot *slot, if (!file) return -EFAULT; + filemap_invalidate_lock_shared(file_inode(file)->i_mapping); + folio = __kvm_gmem_get_pfn(file, slot, index, pfn, max_order); - if (IS_ERR(folio)) - return PTR_ERR(folio); + if (IS_ERR(folio)) { + r = PTR_ERR(folio); + goto out; + } if (!folio_test_uptodate(folio)) { clear_highpage(folio_page(folio, 0)); @@ -780,6 +852,8 @@ int kvm_gmem_get_pfn(struct kvm *kvm, struct kvm_memory_slot *slot, folio_unlock(folio); folio_put(folio); +out: + filemap_invalidate_unlock_shared(file_inode(file)->i_mapping); return r; } EXPORT_SYMBOL_FOR_KVM_INTERNAL(kvm_gmem_get_pfn); @@ -909,6 +983,15 @@ static struct inode *kvm_gmem_alloc_inode(struct super_block *sb) mpol_shared_policy_init(&gi->policy, NULL); + /* + * Memory attributes are protected by the filemap invalidation lock, but + * the lock structure isn't available at this time. Immediately mark + * maple tree as using external locking so that accessing the tree + * before it's fully initialized results in NULL pointer dereferences + * and not more subtle bugs. + */ + mt_init_flags(&gi->attributes, MT_FLAGS_LOCK_EXTERN | MT_FLAGS_USE_RCU); + gi->flags = 0; INIT_LIST_HEAD(&gi->gmem_file_list); return &gi->vfs_inode; @@ -916,7 +999,26 @@ static struct inode *kvm_gmem_alloc_inode(struct super_block *sb) static void kvm_gmem_destroy_inode(struct inode *inode) { - mpol_free_shared_policy(&GMEM_I(inode)->policy); + struct gmem_inode *gi = GMEM_I(inode); + + mpol_free_shared_policy(&gi->policy); + + /* + * Note! Checking for an empty tree is functionally necessary + * to avoid explosions if the tree hasn't been fully + * initialized, i.e. if the inode is being destroyed before + * guest_memfd can set the external lock, lockdep would find + * that the tree's internal ma_lock was not held. + */ + if (!mtree_empty(&gi->attributes)) { + /* + * Acquire the invalidation lock purely to make lockdep happy, + * the inode is unreachable at this point. + */ + filemap_invalidate_lock(inode->i_mapping); + __mt_destroy(&gi->attributes); + filemap_invalidate_unlock(inode->i_mapping); + } } static void kvm_gmem_free_inode(struct inode *inode) -- 2.55.0.897.gb25b4bd76c-goog