From mboxrd@z Thu Jan 1 00:00:00 1970 Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.remote-ip=100.103.45.18 ARC-Seal: i=1; d=subspace.kernel.org; s=arc20261015; a=rsa-sha256; cv=none; t=1792798310; b=jcHTX/pmtHkTyrrHW0wZvIr/0POj7diuYPjQrcJjWDgLCYYRF7ckvoye6VSyB3IEQLxf IXkxG4Vg65nCtCe/S42W9cZGWx2wxi1UDw6rBmrlmw8/yCknF08op2RImR3IdWHSRrUrq GwxevXGl1p603yER5y/LOpqNPcWTvJX+XL5y+OzuxrfwokqiKrcJNdtAW3dxdPdqy4XzQ aWwXGRnaHiKLpUkgtQibUCIEL84YjhdryAui5zA3L/Xn05xs7ZpDhTHclLO7CDx3JRsGa WjLUILQ/Nrtfoi8/GAA0ZmjB7TyBHpH1Eh7F78CTNZ0Xwrh5GbTvfxrJLgNO3ecARNA== ARC-Message-Signature: i=1; d=subspace.kernel.org; s=arc20261015; a=rsa-sha256; c=relaxed/relaxed; t=1792798310; h=Received:DKIM-Signature:Message-ID:From:Subject:Reply-To:To:Cc: In-Reply-To:References:Content-Type:Content-Transfer-Encoding:Date; bh=N6oew5qL/EGvyQxxsjUH/pbhr45NldZJXrfEfFnr/kk=; b=cOtgHoQWKuSqPqvVK0liy7hNnRRGz3Kjx5bH3eZGlRfudSrYbdJk5iDD7uHomMpOV9JM 1vsYyJZYYKVSUCWEbjibF2AAJvDU/Cj7sagCbRVvi4t2zI8l3woesotQK7k7oj87KGTkT lZ9ooyXArsh4x3fKSiR12ulZLV7PpIfoUS1usAEio9UxO8Gai3fiqJTrjuRF62MfbkYZw SGEJjFREHOj7ft9DMo9j3MdReLA91e4iK5nIp/yQfTLQemX7neHknOcyM0Z4dCoMlG20f FIbFZfHCGRt6ACkfqhP8+byzbzJP6ZeCmcXz9R7kSWA1qz9LuAoXT8XjWSTEVAJhBXA== ARC-Authentication-Results: i=1; smtp.subspace.kernel.org; dkim=pass header.d=kernel.org header.i=@kernel.org header.a=rsa-sha256 header.s=k20260515 header.b=LRKQCUm4; arc=none smtp.remote-ip=100.103.45.18 Received: from smtp.kernel.org (quasi.space.kernel.org [100.103.45.18]) (using TLSv1.3 with cipher TLS_AES_256_GCM_SHA384 (256/256 bits) key-exchange X25519 server-signature ECDSA (prime256v1)) (No client certificate requested) by smtp.subspace.kernel.org (Postfix) with ESMTPS id 63B11606A31A for ; Fri, 23 Oct 2026 23:31:50 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; dkim=pass (2048-bit key, unprotected) header.d=kernel.org header.i=@kernel.org header.a=rsa-sha256 header.s=k20260515 header.b=LRKQCUm4 Received: by smtp.kernel.org (Postfix) with ESMTPSA id 3FF941F01828; Fri, 23 Oct 2026 23:31:46 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=kernel.org; s=k20260515; t=1792798310; bh=N6oew5qL/EGvyQxxsjUH/pbhr45NldZJXrfEfFnr/kk=; h=From:Subject:Reply-To:To:Cc:In-Reply-To:References:Date; b=LRKQCUm4Jw1b23J1ePMQCSwNabSprFxLieX6tQdjDJig9B3j5T4HQUPoDoQDRrfCI FdD2n0HrhiKjTtoDcKOhrQMNki7/pe1rRywLIv8AO68MLtP0RESd3ssZfc2RuH1nxS /KjcaKx/rY0GlMeuGqdj67n/m028GgXdYuE/LS3hKoKuDWj0Kk+WHHWSXcHkg2WOX8 anZq/J2JuIqGTbiK1W2O5g83IgOoADQ9LR9S/DN/R7LQr85fS8x+LJuTJxbsWKITZZ OECtgSL1Y2Y42BzyxmYcnXwh3O0m//I8YK7Cq6Lw6iFWnOfiCR6CzSMEjAsxPhBdBr DO5bl7ZJilUGw== Message-ID: From: sashiko-bot@kernel.org Subject: Re: [PATCH RFC v2 04/50] KVM: guest_memfd: Support provider folio invalidation Reply-To: sashiko-reviews@lists.linux.dev To: "Ackerley Tng" , "Alex Williamson" , "Alexander Graf" , "Alexander Viro" , "Alexey Kardashevskiy" , "Andrew Morton" , "Aneesh Kumar K.V" , "Ashish Kalra" , "Baolin Wang" , "Baolu Lu" , "Bill Wendling" , "Borislav Petkov" , "Catalin Marinas" , "Christian Brauner" , =?utf-8?b?Q2hyaXN0aWFuIEvDtm5pZw==?= , "Connor Williamson" , "Dave Hansen" , "Dave Jiang" , "David Hildenbrand" , "David Rientjes" , "David Woodhouse" , "Erdem Aktas" , "Frank van der Linden" , "Fred Griffoul" , "Fred Griffoul" , "Gregory Price" , "H. Peter Anvin" , "Hugh Dickins" , "Ingo Molnar" , "Jacob Pan" , "James Houghton" , "Jan Kara" , "Jason Gunthorpe" , "Jianxiong Gao" , "Joerg Roedel" , "Joey Gouly" , "John Starks" , "Jonathan Corbet" , "Justin Stitt" , "Kevin Tian" , "Lorenzo Stoakes" , "Marc Zyngier" , "Michael Roth" , "Mike Rapoport" , "Nathan Chancellor" , "Nick Desaulniers" , "Nicolin Chen" , "Oliver Upton" , "Paolo Bonzini" , "Pratyush Yadav" , "Randy Dunlap" , "Robin Murphy" , "Samiullah Khawaja" , "Sean Christopherson" , "Shuah Khan" , "Steffen Eiden" , "Steven Price" , "Suzuki K Poulose" , "Tarun Sahu" , "Thomas Gleixner" , "Tom Lendacky" , "Tycho Andersen" , "Vishal Annapurve" , "Vlastimil Babka" , "Will Deacon" , "Xu Yilun" , "Yan Zhao" , "Zenghui Yu" , x86@kernel.org, "Shuah Khan" , "Fuad Tabba" Cc: kvm@vger.kernel.org, linux-mm@kvack.org In-Reply-To: <20261022-gmem-alternative-providers-v2-4-5dd1dc6c660a@google.com> References: <20261022-gmem-alternative-providers-v2-0-5dd1dc6c660a@google.com> <20261022-gmem-alternative-providers-v2-4-5dd1dc6c660a@google.com> Content-Type: text/plain; charset=utf-8 Content-Transfer-Encoding: quoted-printable Date: Fri, 23 Oct 2026 23:31:45 +0000 X-Mailing-List: kvm@vger.kernel.org List-Id: List-Post: List-Help: List-Subscribe: List-Unsubscribe: List-Owner: Precedence: list Thank you for your contribution! Sashiko AI review found 1 potential issue(= s) to consider: - [High] KVM: guest_memfd: AS_RELEASE_ALWAYS without release_folio() in kvm= _gmem_aops -- commit 761ef1ff98198357ffc1c8f5492a708cb9b2d9ab Author: Ackerley Tng KVM: guest_memfd: Support provider folio invalidation This commit adds a provider invalidate_folio callback to guest_memfd and wi= res it up to address_space_operations.invalidate_folio and the filemap_add_foli= o() error path in kvm_gmem_get_folio(). It also sets AS_RELEASE_ALWAYS on the inode mapping in kvm_gmem_init_inode() so truncate_cleanup_folio() invokes .invalidate_folio. > diff --git a/virt/kvm/guest_memfd.c b/virt/kvm/guest_memfd.c > index 545c3e646e9c1..ee823f2ef0368 100644 > --- a/virt/kvm/guest_memfd.c > +++ b/virt/kvm/guest_memfd.c [ ... ] > @@ -942,10 +950,24 @@ static void kvm_gmem_free_folio(struct folio *folio) > } > #endif > =20 > +static void kvm_gmem_invalidate_folio(struct folio *folio, size_t offset, > + size_t len) > +{ > + struct inode *inode =3D folio->mapping->host; > + struct gmem_inode *gi =3D GMEM_I(inode); > + > + /* guest_memfd only allows truncating full folios. */ > + if (WARN_ON_ONCE(offset !=3D 0 || len !=3D folio_size(folio))) > + return; > + > + gmem_provider_invalidate_folio(gi, folio); > +} > + > static const struct address_space_operations kvm_gmem_aops =3D { > .dirty_folio =3D noop_dirty_folio, > .migrate_folio =3D kvm_gmem_migrate_folio, > .error_remove_folio =3D kvm_gmem_error_folio, > + .invalidate_folio =3D kvm_gmem_invalidate_folio, > #ifdef CONFIG_HAVE_KVM_ARCH_GMEM_RECLAIM > .free_folio =3D kvm_gmem_free_folio, > #endif > @@ -984,6 +1006,7 @@ static int kvm_gmem_init_inode(struct inode *inode, = loff_t size, u64 flags) > */ > mapping_set_inaccessible(inode->i_mapping); > WARN_ON_ONCE(!mapping_unevictable(inode->i_mapping)); > + mapping_set_release_always(inode->i_mapping); > =20 > gi->flags =3D flags; > =20 [Severity: High] Does setting mapping_set_release_always() in kvm_gmem_init_inode() without providing a .release_folio callback in kvm_gmem_aops cause filemap_release_= folio() to fall back to try_to_free_buffers() and allow mapping_evict_folio() to ev= ict guest_memfd folios? When AS_RELEASE_ALWAYS is set, folio_needs_release(folio) returns true. If mapping->a_ops->release_folio is NULL, filemap_release_folio() falls through to try_to_free_buffers(): mm/filemap.c:filemap_release_folio() { if (!folio_needs_release(folio)) return true; if (folio_test_writeback(folio)) return false; if (mapping && mapping->a_ops->release_folio) return mapping->a_ops->release_folio(folio, gfp); return try_to_free_buffers(folio); } fs/buffer.c:try_to_free_buffers() { /* Misconfigured folio check */ if (WARN_ON_ONCE(!folio_buffers(folio))) return true; } When a folio is allocated in kvm_gmem_get_folio(), filemap_add_folio() plac= es it on the unevictable LRU with PG_lru set. If the folio is not mapped into userspace page tables (such as private guest_memfd folios or unmapped shared folios, even while mapped in KVM Stage-2/TDP page tables), its refcount is 1 and it is clean. If soft_offline_page() in mm/memory-failure.c runs on that PFN (or if __do_fault() in mm/memory.c encounters a PageHWPoison guest_memfd folio), it calls mapping_evict_folio() in mm/truncate.c: soft_offline_page() -> get_hwpoison_page() -> soft_offline_in_use_page() -> mapping_evict_folio() -> filemap_release_folio() -> try_to_free_buffers() -> remove_mapping() Because mapping_evict_folio() does not check mapping_unevictable(), it calls filemap_release_folio(), triggers WARN_ON_ONCE(!folio_buffers(folio)) in try_to_free_buffers(), and receives true. It then proceeds to remove_mappin= g(), which removes the folio from inode->i_mapping without holding filemap_invalidate_lock, without zapping KVM Stage-2 mappings, and without invoking kvm_gmem_invalidate_folio(), leaking the provider's allocation accounting (such as tmpfs sbinfo->used_blocks). Should kvm_gmem_aops also implement .release_folio (or avoid mapping_set_release_always()) so that filemap_release_folio() does not fall through to try_to_free_buffers() and permit eviction via mapping_evict_foli= o()? --=20 Sashiko AI review =C2=B7 https://sashiko.dev/#/patchset/20261022-gmem-alter= native-providers-v2-0-5dd1dc6c660a@google.com?part=3D4