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=1793820173; b=ZnqIl1xUJfhJUHBCshDd3eCmOStjEjqJMJ/LVSfB23S4aEgczMjjgDi7esivErFb/z9C 4On2aR0ASoBZWNdvqn5v9WOAUdc5/+yjQnOZKtVITd105oqw/89YKqT17GEnQvFr4ZE9z gSKcZ76YE27qSi3Hw4Y3DN3G/IjI0BhcGQg8a8Y8P6tlrlWo2FRchA7a8VvCHWNZss4Iu PxSo55iAfqcIUKSC+ajOssBzRGX1fVwSkrCsOepUGsqRvqZHGvU7Et9c8Ng9j9KiTTOTh eNXQ/qdXIbm2UlvAuY4YRtUVIHB6IU/jxLPxVCwAPC5h0SjpH6rZ9viS+Nswa7Qw02g== ARC-Message-Signature: i=1; d=subspace.kernel.org; s=arc20261015; a=rsa-sha256; c=relaxed/relaxed; t=1793820173; h=Received:DKIM-Signature:Subject:To:Cc:From:Date:Message-ID: MIME-Version:Content-Type:Content-Transfer-Encoding; bh=b+dKPKBiHusdRq8k+f2Xcxy60hmat6uaNJGaWRyDLzQ=; b=0OUVNbe35ZGRXHjccNs4BjcWW2lQXOb1yE6xnuByWK8FqNdQAIrCVwzdMwhQfrV+2dRM pGvMPq+bFaHfh8HcpJLJUdrMoz7gA+kzSExjoeB4/Wuk/Hp4MzRpHYv+fStxrHeu1wlKc RHV/V0xwpaqmQutL2Qx15zepLx69PZtnLQ99huK3OYN+oAFtTvRhM6ufTSOn6VA5XiNnw /mCq7B6/j57mZwriP+WVim3mWy5JusWOOz5vMnGN672RJ9216CJRdX5QeGNakOG2Rot/d DtYwDausodcq0keuPSt5lc/yTfw0GLFT5tYp1sTkSZqqL6O1lo5j6kUgYgjPerw67yw== 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=OJxhLLlR; 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 E5031607894A for ; Wed, 4 Nov 2026 19:22:52 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; dkim=pass (1024-bit key, unprotected) header.d=linuxfoundation.org header.i=@linuxfoundation.org header.a=rsa-sha256 header.s=korg header.b=OJxhLLlR Received: by smtp.kernel.org (Postfix) with ESMTPSA id 64A2F1F0093A; Wed, 4 Nov 2026 19:22:52 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=linuxfoundation.org; s=korg; t=1793820172; bh=b+dKPKBiHusdRq8k+f2Xcxy60hmat6uaNJGaWRyDLzQ=; h=Subject:To:Cc:From:Date; b=OJxhLLlRPI+Fft47CA3j519I506u9uy9rE5lEh400jPUM+kayyCr4kX5ddjoRpo+r zP3FG55u0jrw/HTecMhXBDABuVV5qZXys1PMmGzUfPkkDrFUP7rTkEUoItYGqSoSWO RbTywYXuMNwD2VjJzJMRG5Eulp5ufgXGOJVS/XIU= Subject: FAILED: patch "[PATCH] KVM: guest_memfd: take the invalidate lock when unbinding a" failed to apply to 6.12-stable tree To: shivankg@amd.com,david@kernel.org,sashiko-bot@kernel.org,seanjc@google.com Cc: From: Date: Wed, 04 Nov 2026 14:22:43 -0500 Message-ID: <2026110443-wham-canine-0ce3@gregkh> 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-Type: text/plain; charset=ANSI_X3.4-1968 Content-Transfer-Encoding: 8bit The patch below does not apply to the 6.12-stable tree. If someone wants it applied there, or to any other stable or longterm tree, then please email the backport, including the original git commit id to . To reproduce the conflict and resubmit, you may use the following commands: git fetch https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/ linux-6.12.y git checkout FETCH_HEAD git cherry-pick -x 0ee2c883b62deb74d8c43007e8049dc006d3a2fb # git commit -s git send-email --to '' --in-reply-to '2026110443-wham-canine-0ce3@gregkh' --subject-prefix 'PATCH 6.12.y' 'HEAD^..' Possible dependencies: thanks, greg k-h ------------------ original commit in Linus's tree ------------------ >From 0ee2c883b62deb74d8c43007e8049dc006d3a2fb Mon Sep 17 00:00:00 2001 From: Shivank Garg Date: Tue, 1 Sep 2026 07:20:38 +0000 Subject: [PATCH] KVM: guest_memfd: take the invalidate lock when unbinding a dying file 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 diff --git a/virt/kvm/guest_memfd.c b/virt/kvm/guest_memfd.c index 625e62e1a031..21bb3710edfe 100644 --- a/virt/kvm/guest_memfd.c +++ b/virt/kvm/guest_memfd.c @@ -668,11 +668,33 @@ 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 gmem_file *f) +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; + struct gmem_file *f; + /* + * Nothing to do if the underlying file was _already_ closed, as + * kvm_gmem_release() invalidates and nullifies all bindings. + */ + if (!file) + return; + + /* + * 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. 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. + */ + f = file->private_data; + + filemap_invalidate_lock(file->f_mapping); xa_store_range(&f->bindings, start, end - 1, NULL, GFP_KERNEL); /* @@ -680,36 +702,6 @@ static void __kvm_gmem_unbind(struct kvm_memory_slot *slot, struct gmem_file *f) * cannot see this memslot. */ WRITE_ONCE(slot->gmem.file, NULL); -} - -void kvm_gmem_unbind(struct kvm_memory_slot *slot) -{ - /* - * Nothing to do if the underlying file was _already_ closed, as - * kvm_gmem_release() invalidates and nullifies all bindings. - */ - if (!slot->gmem.file) - return; - - CLASS(gmem_get_file, 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. - */ - if (!file) { - __kvm_gmem_unbind(slot, slot->gmem.file->private_data); - return; - } - - filemap_invalidate_lock(file->f_mapping); - __kvm_gmem_unbind(slot, file->private_data); filemap_invalidate_unlock(file->f_mapping); }