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=1794590063; b=xQHSoZ88msJFSo3IcS1ixxMjqKYdXuaqIeViuDueFdCQ4w5AoGyWojzKzwBmgHwNzD+X +QcHdMnoJYiJ5kZBeyS3yhES+w7bg9Z2P8y2ljF3nC6aWjCPjUtwRh5MGmnxXwdhu+xYH fVBf8enqY2F+lmljQ5EuSM+hPmmK0KYdlKEzYCHJAPXInRwBklF5nC8/KUx7qwWTgsAPI XgyUD5z3AdTT+PHZW9HaCQYczEuPJCNn+dzndMw73SLP6s37CSouwqdlA8RsQlMj+VgWj YBdKTEsjHat+ftA5/VNlvPHglLHLAM3qzOcJ2bhcndBvs7ezT5JmMz2ohReLbUpT/Cg== ARC-Message-Signature: i=1; d=subspace.kernel.org; s=arc20261015; a=rsa-sha256; c=relaxed/relaxed; t=1794590063; h=Received:DKIM-Signature:From:To:Cc:Subject:Date:Message-ID:X-Mailer: In-Reply-To:References:User-Agent:X-stable:X-Patchwork-Hint: MIME-Version:Content-Transfer-Encoding; bh=b0jDDU3KCNjNLT2qoLaXPKoYi1KCQ6sLAKppjwZz6QM=; b=Hf/wUZIz8YndmczMD4uIlEOraCSKMtOjnGyx4RkrR0kxWb9SrWyffMvPW0ti2LKpCYr+ 03MxWoaBVQli2pYqTTYdYbsRUh5NYA9DvIiKEi5xfeZKhiJoP6wFAXVSx6gYWr96p1h2l AQlQI7hyakXndtJOnEDJw/i1ofhY0+Nr1Vg706Ja5bChSNHasYPW0vnMtNxRNncg2oleW 3LdK6vgqD3YprVJgcGjssdLJ84WYLeweKuv/F3ZMuQ7MsCI1SNV4zyUE12ckTB6kddW9Q dI8/Mi2SMLTBMBtmfTVCwbCsvchBtFNqY7WH19kzYC6vb1eNgygpviaQ3X5Qatx47pA== ARC-Authentication-Results: i=1; smtp.subspace.kernel.org; dkim=pass header.d=linuxfoundation.org header.i=@linuxfoundation.org header.a=rsa-sha256 header.s=korg header.b=oiEJfLdp; 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 4812A606A335; Fri, 13 Nov 2026 17:14:23 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; dkim=pass (1024-bit key) header.d=linuxfoundation.org header.i=@linuxfoundation.org header.a=rsa-sha256 header.s=korg header.b=oiEJfLdp Received: by smtp.kernel.org (Postfix) with ESMTPSA id E8B231F000C5; Fri, 13 Nov 2026 17:14:22 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=linuxfoundation.org; s=korg; t=1794590063; bh=b0jDDU3KCNjNLT2qoLaXPKoYi1KCQ6sLAKppjwZz6QM=; h=From:To:Cc:Subject:Date:In-Reply-To:References; b=oiEJfLdpqeB+CXF8rroR35UlP9QnchXhaWRP1m47ehvOQlGcUx4sP3Dw92xC1AcUC nqfvicTCBZONdznOHvOz5jpALzZvOLrGjjvaIxtMRjggNWlBhnUK1x3cuk/qr82DC5 cuUWY3OQ9y8QuZ3w4Ph6ENU3dXlb2H+N93RoOrss= From: Greg Kroah-Hartman To: stable@vger.kernel.org Cc: Greg Kroah-Hartman , patches@lists.linux.dev, Sashiko , Sean Christopherson , Shivank Garg , "David Hildenbrand (Arm)" , Sasha Levin Subject: [PATCH 6.18 053/686] KVM: guest_memfd: take the invalidate lock when unbinding a dying file Date: Fri, 13 Nov 2026 10:43:06 -0500 Message-ID: <20261113153822.759550199@linuxfoundation.org> X-Mailer: git-send-email 2.56.0 In-Reply-To: <20261113153820.902362109@linuxfoundation.org> References: <20261113153820.902362109@linuxfoundation.org> User-Agent: quilt/0.69 X-stable: review X-Patchwork-Hint: ignore X-Mailing-List: stable@vger.kernel.org List-Id: List-Post: List-Help: List-Subscribe: List-Unsubscribe: List-Owner: Precedence: list MIME-Version: 1.0 Content-Transfer-Encoding: 8bit 6.18-stable review patch. If anyone has any objections, please let me know. ------------------ From: Shivank Garg [ Upstream commit 0ee2c883b62deb74d8c43007e8049dc006d3a2fb ] kvm_gmem_unbind() takes mapping->invalidate_lock only if the get_file_active() succeeds. When the guest_memfd file is dying, its reference count is already zero so get_file_active fails and the binding is removed without holding the invalidate lock. kvm_gmem_invalidate_{start,end}() checks f->bindings independently to decide whether to begin or end KVM MMU invalidation. So, the bindings must therefore remain stable between the two calls. Otherwise, unbind can remove a binding after start increments mmu_invalidate_in_progress, but before end finds the binding and decrements it. Example, unbind race with memory failure: CPU 0: memory failure CPU 1: memslot delete ---------------------------------- --------------------------- (guest_memfd file is dying) kvm_gmem_error_folio() kvm_gmem_invalidate_start() finds binding mmu_invalidate_in_progress++ kvm_gmem_unbind() get_file_active() fails removes binding kvm_gmem_invalidate_end() no binding found counter stays elevated mmu_invalidate_retry() then returns 1 forever, so guest page faults retry without ever installing a mapping and the guest hangs. Remove the distinction between live and dying files in the unbind path. Always use slot->gmem.file and take the invalidate lock when it's non-NULL. Normal unbind callers hold slots_lock, which prevents release from clearing the pointer or freeing the file state until unbind completes. Final VM teardown can only see a NULL pointer because guest_memfd pins the KVM until release has cleared all bindings. Fixes: ae431059e75d ("KVM: guest_memfd: Remove bindings on memslot deletion when gmem is dying") Cc: stable@vger.kernel.org Reported-by: Sashiko Closes: https://lore.kernel.org/all/20260728092027.225CF1F000E9@smtp.kernel.org Suggested-by: Sean Christopherson Signed-off-by: Shivank Garg Reviewed-by: David Hildenbrand (Arm) Link: https://patch.msgid.link/20260901-gmem-unbind-fix-v2-1-12febe1d2216@amd.com Signed-off-by: Sean Christopherson [ sashal: Adapted unbind to struct kvm_gmem with explicit kvm_gmem_get_file()/fput() removal replacing upstream's automatic cleanup removal. ] Signed-off-by: Sasha Levin --- virt/kvm/guest_memfd.c | 48 ++++++++++++++++-------------------------- 1 file changed, 18 insertions(+), 30 deletions(-) diff --git a/virt/kvm/guest_memfd.c b/virt/kvm/guest_memfd.c index 2ab7bb46a371e..5f9a25fa0a09b 100644 --- a/virt/kvm/guest_memfd.c +++ b/virt/kvm/guest_memfd.c @@ -635,53 +635,41 @@ int kvm_gmem_bind(struct kvm *kvm, struct kvm_memory_slot *slot, return r; } -static void __kvm_gmem_unbind(struct kvm_memory_slot *slot, struct kvm_gmem *gmem) +void kvm_gmem_unbind(struct kvm_memory_slot *slot) { + struct file *file = slot->gmem.file; unsigned long start = slot->gmem.pgoff; unsigned long end = start + slot->npages; - - xa_store_range(&gmem->bindings, start, end - 1, NULL, GFP_KERNEL); - - /* - * synchronize_srcu(&kvm->srcu) ensured that kvm_gmem_get_pfn() - * cannot see this memslot. - */ - WRITE_ONCE(slot->gmem.file, NULL); -} - -void kvm_gmem_unbind(struct kvm_memory_slot *slot) -{ - struct file *file; + struct kvm_gmem *gmem; /* * Nothing to do if the underlying file was _already_ closed, as * kvm_gmem_release() invalidates and nullifies all bindings. */ - if (!slot->gmem.file) + if (!file) return; - file = kvm_gmem_get_file(slot); - /* * However, if the file is _being_ closed, then the bindings need to be * removed as kvm_gmem_release() might not run until after the memslot - * is freed. Note, modifying the bindings is safe even though the file - * is dying as kvm_gmem_release() nullifies slot->gmem.file under - * slots_lock, and only puts its reference to KVM after destroying all - * bindings. I.e. reaching this point means kvm_gmem_release() hasn't - * yet destroyed the bindings or freed the gmem_file, and can't do so - * until the caller drops slots_lock. + * is freed. Modifying the bindings is safe even if the file is dying + * as kvm_gmem_release() nullifies slot->gmem.file under slots_lock, + * and only puts its reference to KVM after destroying all bindings. + * I.e. reaching this point means kvm_gmem_release() hasn't destroyed + * the bindings or freed the gmem_file and can't do so until the caller + * drops slots_lock, so there's no need to verify the file is live. */ - if (!file) { - __kvm_gmem_unbind(slot, slot->gmem.file->private_data); - return; - } + gmem = file->private_data; filemap_invalidate_lock(file->f_mapping); - __kvm_gmem_unbind(slot, file->private_data); - filemap_invalidate_unlock(file->f_mapping); + xa_store_range(&gmem->bindings, start, end - 1, NULL, GFP_KERNEL); - fput(file); + /* + * synchronize_srcu(&kvm->srcu) ensured that kvm_gmem_get_pfn() + * cannot see this memslot. + */ + WRITE_ONCE(slot->gmem.file, NULL); + filemap_invalidate_unlock(file->f_mapping); } /* Returns a locked folio on success. */ -- 2.53.0