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=1793974421; b=MMmUxibdQU1pr0tV6zuzLEMAOTdW3iieb26DTdisJNwKJcf2Q4vg/t7CXinX/OqrSJWe Ovge+u/nXVDjIjRimoUttNQaoQ3mffDcMioHZyw+cij2XoZx97kBIPg2lYuYqGhU9OHCA XmGElE0JVElXtEp/DFUdnA+MoSLrPgldWAe/mA4kU9qVxazBXnjP94BFnQY3s6OQGXalR o+Kbj5nH7E4qRjbOwMH8Q8hYvfZy6Isk5XoR2EZXz2RpO1P10220Ruidt7hVnwWu+Y2nL ZBIeDdW2B49+r8n8xIR5uLa+tEtEzlb9uPGbYdIVGWmjW0lz5Vq23t4cwkKTGWFqp0g== ARC-Message-Signature: i=1; d=subspace.kernel.org; s=arc20261015; a=rsa-sha256; c=relaxed/relaxed; t=1793974421; h=Received:DKIM-Signature:From:To:Cc:Subject:Date:Message-ID:X-Mailer: In-Reply-To:References:MIME-Version:Content-Transfer-Encoding; bh=hwqHqfPbvqPsYJ/6jw8FyV9u20mx881DKftZYCYE5CA=; b=Qky8Og4NS1/TKHleECYGncWbetM0mIFtYPr3lIFJlEfP974VdgUwSmuj4SPguDs0lBvf Rchk8nzt3iEh2rST0RnU0DL6KqQmvjkpU93owVClEb/UgTaLI1w2T0ElB698ZyicsZKd+ +NpmPqmqUDl7RaoZkxU2EXrBk1NO70MwW7gAJCb/5veY3xZ5TmkVa+T+9n8NQgiap21Pu dbtCnmrhrgQ7T9b2qrYvIwSLGJXj/AFvZgy5yntCrPEMEvJtS54ic1GbH3FZp9gmRbm3B bclelacJrb+BslYe4wvpd7g7WR/vknIxlhVjnNf1/3f7CUlrZ+B3PVLAHJLY0Ab89eA== 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="hap/gnbH"; 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 9D4AF606A326 for ; Fri, 6 Nov 2026 14:13:41 +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=hap/gnbH Received: by smtp.kernel.org (Postfix) with ESMTPSA id 93C3E1F0089F; Fri, 6 Nov 2026 14:13:40 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=kernel.org; s=k20260515; t=1793974421; bh=hwqHqfPbvqPsYJ/6jw8FyV9u20mx881DKftZYCYE5CA=; h=From:To:Cc:Subject:Date:In-Reply-To:References; b=hap/gnbH7xtmR80leNScGbzVPSAT46n36U+BjSg8NssE6hVVmlSxSWJxOv1AmCkvk CegqSCKtdSouKqgV+wDE2CC+aBp2CbKJ95lOIwpzaD/GZND0oiLJ+P5Cwm466ZbOOU D5P5qHkk2KvzitQDKakk1/jCrXtUjsmBb8myEgQvTaQhEUUs68jOQUqdsuTopOEn/g 3g8N/cwuNuZZ/oI/xh30sET7bafRC03mZdM1O8BFRj8OnNH93Li+qNksj5/qTSP4EI 7NIh0eD5qV73PYhWAXAHvIwcqO+KkhgQtJyXGhQ+HHCj8YDj0kMLSj8H/knunDf6ny ist36WHORzGwg== From: Sasha Levin To: stable@vger.kernel.org Cc: Shivank Garg , Sashiko , Sean Christopherson , "David Hildenbrand (Arm)" , Sasha Levin Subject: [PATCH 6.18.y] KVM: guest_memfd: take the invalidate lock when unbinding a dying file Date: Fri, 6 Nov 2026 09:13:39 -0500 Message-ID: <20261106141257.320136-1-sashal@kernel.org> X-Mailer: git-send-email 2.53.0 In-Reply-To: <2026110442-recast-sequel-2c6a@gregkh> References: <2026110442-recast-sequel-2c6a@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-Transfer-Encoding: 8bit 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 a59a4446b8461..e121534e21692 100644 --- a/virt/kvm/guest_memfd.c +++ b/virt/kvm/guest_memfd.c @@ -627,53 +627,41 @@ 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