From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from mail-pl1-f202.google.com (mail-pl1-f202.google.com [209.85.214.202]) (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 9B58E21A434 for ; Wed, 15 Apr 2026 22:15:13 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=209.85.214.202 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1776291314; cv=none; b=n8l5yZd8rJISkd9og+dbgIn5kgXaCE/78a1qIR2m0KQUaDrBN1vqdCPEqDUMybx63dsyLfKE788DRVB+nRF8gOYjwCXA0HyM2oJHk7bLXMkCFHIAsaQU1n9f5Z6z3/Msz7IhlzdVM3/dD/McSo+2JVx4LavQ2hjBlcqTcNTFAwQ= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1776291314; c=relaxed/simple; bh=CcCwRytegUwsJjSZ6eoAOigRploRUfqEvFZTbZletZE=; h=Date:In-Reply-To:Mime-Version:References:Message-ID:Subject:From: To:Cc:Content-Type; b=b0K9GVhxYerW3Wq1dW66y4N+TvMjrwCfvAO4+YgEy3YLjmIXwxgDhP37g8ydm389yjMvZH5K2eIr0shgZw/baVXCrQUVTbCom+9pKeVYl+CCbYQPtGiAwy9MVaY7QTZb/F3fr7JF08OosTUBgk1pEwRHnOd9fSkgxQNDHbXNVDE= 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=dp7oMaNQ; arc=none smtp.client-ip=209.85.214.202 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="dp7oMaNQ" Received: by mail-pl1-f202.google.com with SMTP id d9443c01a7336-2b2e91add2aso44901525ad.1 for ; Wed, 15 Apr 2026 15:15:13 -0700 (PDT) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=google.com; s=20251104; t=1776291313; x=1776896113; 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=EGo4VOJQPFyHusz55hlkxA3lp3eULjapJ3aQapxGGCk=; b=dp7oMaNQCXmdryY/a+4Ax1iepQ9QP/eCbZmAhAChGTB7RxWErk520Nli6D7JPUofCw gkxnbw30pOCWTdDWBDcMYvIL7UsI8c/t6WqrdN/79aESEvs1EwQx7wtyv1h7YKwlWoUK iV/1vGn2OQEqaRpwRbtUVTapILt2sDj0U3IitozMbSP0lKlNRjpnHZOEgvp8lsGByZLz nw1ksXCzCtkVACeuJCVoHxFK1vGtdvQeynHnr9xpmtuLUC281vxq6eC5suB60bCvzj9t 4Fi+d0tt2U5g6orWsJ5vpfJo+Kqxrs04uDik0zoUwJbX1W0tdgLJ4eweOAvPixOFYQi8 UVFQ== X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20251104; t=1776291313; x=1776896113; 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=EGo4VOJQPFyHusz55hlkxA3lp3eULjapJ3aQapxGGCk=; b=T/QTEz9KTt82BMnUUBcs9nR0cdNcKcwZVaGBclNYHRc4X6FqzolG7RHtYwAux2L6yw Dr4kNxZvxMdhMfSsyQzhE4ubcrG7a7rgYLsktvld8miAAJ1ebR7ud+izdlOC+jvyrR7M 0Ga5x7kK/1h+CQqZU7mjpj7qZuoCVrGVazzsStYODw003saKOE1FXtY70DgqCDVxyNkl phdNvMTS9MuN5Q5aqRP2JrOETc0ilxkLZhxU62ZeXMS7PrswGxh/3ocRM4ZxXGXM1ecf VCg86KsUpFp8iMncx49nJNA+THxGtK+nNcrNQzNliAivJ+xZPuFJAudPxKsiQ01+Kcwy RJgg== X-Gm-Message-State: AOJu0YyVyJXZkHY+wVBctU8X7+lrvd3a3sfjHXz4THImB8X4flO+6P7I 7ra65bGPFPHJlME8YmwEQO0dshFWK+ry0Vw7GQ1Z3xorNvFM32XrYbPeemMgPLteGzJRKgflBXB Q/og26w== X-Received: from plsc1.prod.google.com ([2002:a17:902:b681:b0:2b0:5e63:fc48]) (user=seanjc job=prod-delivery.src-stubby-dispatcher) by 2002:a17:903:acf:b0:2b2:539b:d29a with SMTP id d9443c01a7336-2b2d5a1525amr241068115ad.23.1776291312762; Wed, 15 Apr 2026 15:15:12 -0700 (PDT) Date: Wed, 15 Apr 2026 15:15:11 -0700 In-Reply-To: <20260413140746.2904035-2-sashal@kernel.org> Precedence: bulk X-Mailing-List: stable@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: Mime-Version: 1.0 References: <2026041318-chowder-paper-ef87@gregkh> <20260413140746.2904035-1-sashal@kernel.org> <20260413140746.2904035-2-sashal@kernel.org> Message-ID: Subject: Re: [PATCH 6.12.y 2/2] 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 > Signed-off-by: Sasha Levin > --- Acked-by: Sean Christopherson