From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from mail-pg1-f202.google.com (mail-pg1-f202.google.com [209.85.215.202]) (using TLSv1.2 with cipher ECDHE-RSA-AES128-GCM-SHA256 (128/128 bits)) (No client certificate requested) by smtp.subspace.kernel.org (Postfix) with ESMTPS id 6C1EC386C06 for ; Wed, 15 Apr 2026 21:58:51 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=209.85.215.202 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1776290332; cv=none; b=ToBwWevQau8OEXCyZ+jKgItmp3BGsySLdOnonE9kfmpGiI7hpZ9Jd8JsvYXsCiea+63nooiHfZzpM7m9vG83WGlEzIMeUX95/Oj+Usj1qVH4UJYY/6UEIyJotRL177NOIQNOMUeFb7udoQgf7CSTfY+ImTl4oCBxRIfDfhPl950= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1776290332; c=relaxed/simple; bh=HtHHQLyFrpyRD1K6YTlLXaKgJ56SQTDZhkN7NWqJQ/w=; h=Date:In-Reply-To:Mime-Version:References:Message-ID:Subject:From: To:Cc:Content-Type; b=lv+rDspmeUyjF94eV6jCOEw0YxIJJTkvufDK2a+x1lBTslcwtEKX3MobENNWPv+NCc6Wd0sFh1VHDVLJaHde+VeqIprYSIXb0Rux/keCx3qdLB1+vmNEMkGd5lzZbrV1SP8Yp0UZewpsekBNDShe8cxIWZzzv1nqS85ss3yX7U4= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dmarc=pass (p=reject dis=none) header.from=google.com; spf=pass smtp.mailfrom=flex--seanjc.bounces.google.com; dkim=pass (2048-bit key) header.d=google.com header.i=@google.com header.b=HZgXOEcI; arc=none smtp.client-ip=209.85.215.202 Authentication-Results: smtp.subspace.kernel.org; dmarc=pass (p=reject dis=none) header.from=google.com Authentication-Results: smtp.subspace.kernel.org; spf=pass smtp.mailfrom=flex--seanjc.bounces.google.com Authentication-Results: smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=google.com header.i=@google.com header.b="HZgXOEcI" Received: by mail-pg1-f202.google.com with SMTP id 41be03b00d2f7-c70dd30025fso9342699a12.2 for ; Wed, 15 Apr 2026 14:58:51 -0700 (PDT) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=google.com; s=20251104; t=1776290331; x=1776895131; darn=vger.kernel.org; h=cc:to:from:subject:message-id:references:mime-version:in-reply-to :date:from:to:cc:subject:date:message-id:reply-to; bh=d9zLiEKj3T6t8ihrer91NOzILwHRxAQN4Wp96+dLSss=; b=HZgXOEcIf6Go8bXyXy7NYDoQn/VHdlLey13h9sA0Kv8kz5k17dUB+7KjPFRPQSiXO0 oKTlpy1FTa9LqhDLhHrBl904PMz7aNLBCtPzMndlh09pnka25763hsLn55K4YL/+nng8 LD36B+KL0QE6cN1rhllTSGsY/MBF4+HmjLZmMrGvzR1ITO52NxU4yedR+gFdDJ6kv5XV zOZp6gWmAVX0V9yhQzBHoYGyNotZITiP//uESeFfhmXDIBqHYuZXsSa7PpyY8Mt7rGZh l8jOdJq2Bz5tjqADhisjTxXNJyMGmk9jD5Z9CABGJN+CGA00emm1W1Zxj5lHPw9NfDb1 2InQ== X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20251104; t=1776290331; x=1776895131; h=cc:to:from:subject:message-id:references:mime-version:in-reply-to :date:x-gm-message-state:from:to:cc:subject:date:message-id:reply-to; bh=d9zLiEKj3T6t8ihrer91NOzILwHRxAQN4Wp96+dLSss=; b=Aui+koQ+TkIUnbQY6znuEoaM4qHkB9jEhyxaCcmW+g5QJd+GV+FMSuuQelTiDyrh9a KdsKk5IGprsiDjnesHEPkDWA5KPPRZp9QpSOWLKa/I2CxlhhrOqp0wY6o6riR6lGomem 9MIxSIzet2FODSwGSrI73JDCYwAVuKvVYUPydQKnp+7rsvqNQLCWs6MC7JXa3YDCj6cM ZXicVRV6yzx0o26fllSjRIQSl/LbLjgSm7b8uLqkbrmMu029k7Js/DBs3eWYXTDt9rFd 0HgmEmr1JFd1at/XfjxsFYnhtnvBaySwWgDHh8cGhqmKAngWJ8/OzCnSq2mbfX+7Lgzn TsMA== X-Gm-Message-State: AOJu0YzxV7mmmoA6ci5SBJZm3qVZgSbr99MChG+6Pq3Xrcrv5we8/zXr 96cFD+Nf4/DwLoQgHsFga6uYf3hD5kEwVtK8kPOpZ7MTZFEdnxCIc+b6Dw2W5Hi1ecY0VxoCp/M Fqxrdlg== X-Received: from pfbdh21.prod.google.com ([2002:a05:6a00:4795:b0:829:f706:70e4]) (user=seanjc job=prod-delivery.src-stubby-dispatcher) by 2002:a05:6a00:4388:b0:82c:ae58:4690 with SMTP id d2e1a72fcca58-82f0c2f17b9mr23341809b3a.52.1776290330560; Wed, 15 Apr 2026 14:58:50 -0700 (PDT) Date: Wed, 15 Apr 2026 14:58:49 -0700 In-Reply-To: <20260413152005.3014972-1-sashal@kernel.org> Precedence: bulk X-Mailing-List: stable@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: Mime-Version: 1.0 References: <2026041319-perceive-bok-f424@gregkh> <20260413152005.3014972-1-sashal@kernel.org> Message-ID: Subject: Re: [PATCH 6.1.y] KVM: x86: Use __DECLARE_FLEX_ARRAY() for UAPI structures with VLAs From: Sean Christopherson To: Sasha Levin Cc: stable@vger.kernel.org, David Woodhouse Content-Type: text/plain; charset="us-ascii" On Mon, Apr 13, 2026, Sasha Levin wrote: > From: David Woodhouse > > [ Upstream commit 2619da73bb2f10d88f7e1087125c40144fdf0987 ] > > Commit 94dfc73e7cf4 ("treewide: uapi: Replace zero-length arrays with > flexible-array members") broke the userspace API for C++. > > These structures ending in VLAs are typically a *header*, which can be > followed by an arbitrary number of entries. Userspace typically creates > a larger structure with some non-zero number of entries, for example in > QEMU's kvm_arch_get_supported_msr_feature(): > > struct { > struct kvm_msrs info; > struct kvm_msr_entry entries[1]; > } msr_data = {}; > > While that works in C, it fails in C++ with an error like: > flexible array member 'kvm_msrs::entries' not at end of 'struct msr_data' > > Fix this by using __DECLARE_FLEX_ARRAY() for the VLA, which uses [0] > for C++ compilation. > > Fixes: 94dfc73e7cf4 ("treewide: uapi: Replace zero-length arrays with flexible-array members") > Cc: stable@vger.kernel.org > Signed-off-by: David Woodhouse > Link: https://patch.msgid.link/3abaf6aefd6e5efeff3b860ac38421d9dec908db.camel@infradead.org > [sean: tag for stable@] > Signed-off-by: Sean Christopherson > [ applied `__DECLARE_FLEX_ARRAY(char, name)` change directly instead of inside missing `#ifdef __KERNEL__` else branch ] > Signed-off-by: Sasha Levin > --- Acked-by: Sean Christopherson