From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from smtp.kernel.org (aws-us-west-2-korg-mail-1.web.codeaurora.org [10.30.226.201]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by smtp.subspace.kernel.org (Postfix) with ESMTPS id A70BF31A053 for ; Mon, 13 Apr 2026 12:08:30 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=10.30.226.201 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1776082110; cv=none; b=MFMlfFia0/HSQyqlyGY4OOW/TlQxtZ3uHG02ts47kwsAF44F3ARCZWoMuUUri4ADVl5YJBXN07aLdff+pkAFBrMeB5ESaYRvfQPND3LXJzhe/pdLlvh1MWz4STILzEI9BSFOyVzPQ+vOdRSadyUki1rlNRsbbfPMXtIf7jOO73I= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1776082110; c=relaxed/simple; bh=I26I8zbOstlcvk80uNcxt2p3olrYSU5YVlV8qwS7AAY=; h=Subject:To:Cc:From:Date:Message-ID:MIME-Version:Content-Type; b=UONXwPRHq2mYygWxqNwI6ySKnYUo4Qfm/JEdEOvMOjzSnaFtZF8Q5/0t7wEc/A3CtCLBtKUD5ZXcq/LEsYykdYRKu1+RyvBYqTsMNeY96JwmtYxXLKYM17mutJKuyhq6NFrsFFU1pYWyuORcnp7MKmHaQHa0LlopAi/561KGm9Y= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dkim=pass (1024-bit key) header.d=linuxfoundation.org header.i=@linuxfoundation.org header.b=RqUZVRps; arc=none smtp.client-ip=10.30.226.201 Authentication-Results: smtp.subspace.kernel.org; dkim=pass (1024-bit key) header.d=linuxfoundation.org header.i=@linuxfoundation.org header.b="RqUZVRps" Received: by smtp.kernel.org (Postfix) with ESMTPSA id 3D6F8C116C6; Mon, 13 Apr 2026 12:08:30 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=linuxfoundation.org; s=korg; t=1776082110; bh=I26I8zbOstlcvk80uNcxt2p3olrYSU5YVlV8qwS7AAY=; h=Subject:To:Cc:From:Date:From; b=RqUZVRpsBHzlq6GSVxiqN8/LqXzkHcMmoBrFvkCmpRjU0dMty9dcBI/G7I0zQxpnd 0Njpp/q9yFbrwZK/8DZ4vz9A8OlWtzt7Drwi0epwq2IC++BvJ3bLPfToJlv1U3GU2R 0A0iTSLZalGp2FooT3MYj2N8KVmehPyHSUdKIZTw= Subject: FAILED: patch "[PATCH] KVM: x86: Use __DECLARE_FLEX_ARRAY() for UAPI structures with" failed to apply to 6.6-stable tree To: dwmw@amazon.co.uk,seanjc@google.com Cc: From: Date: Mon, 13 Apr 2026 14:08:18 +0200 Message-ID: <2026041318-monogamy-woozy-29fe@gregkh> Precedence: bulk X-Mailing-List: stable@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: 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 6.6-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-6.6.y git checkout FETCH_HEAD git cherry-pick -x 2619da73bb2f10d88f7e1087125c40144fdf0987 # git commit -s git send-email --to '' --in-reply-to '2026041318-monogamy-woozy-29fe@gregkh' --subject-prefix 'PATCH 6.6.y' HEAD^.. Possible dependencies: thanks, greg k-h ------------------ original commit in Linus's tree ------------------ >From 2619da73bb2f10d88f7e1087125c40144fdf0987 Mon Sep 17 00:00:00 2001 From: David Woodhouse Date: Thu, 5 Mar 2026 20:49:55 +0100 Subject: [PATCH] KVM: x86: Use __DECLARE_FLEX_ARRAY() for UAPI structures with VLAs 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 diff --git a/arch/x86/include/uapi/asm/kvm.h b/arch/x86/include/uapi/asm/kvm.h index 0d4538fa6c31..5f2b30d0405c 100644 --- a/arch/x86/include/uapi/asm/kvm.h +++ b/arch/x86/include/uapi/asm/kvm.h @@ -197,13 +197,13 @@ struct kvm_msrs { __u32 nmsrs; /* number of msrs in entries */ __u32 pad; - struct kvm_msr_entry entries[]; + __DECLARE_FLEX_ARRAY(struct kvm_msr_entry, entries); }; /* for KVM_GET_MSR_INDEX_LIST */ struct kvm_msr_list { __u32 nmsrs; /* number of msrs in entries */ - __u32 indices[]; + __DECLARE_FLEX_ARRAY(__u32, indices); }; /* Maximum size of any access bitmap in bytes */ @@ -245,7 +245,7 @@ struct kvm_cpuid_entry { struct kvm_cpuid { __u32 nent; __u32 padding; - struct kvm_cpuid_entry entries[]; + __DECLARE_FLEX_ARRAY(struct kvm_cpuid_entry, entries); }; struct kvm_cpuid_entry2 { @@ -267,7 +267,7 @@ struct kvm_cpuid_entry2 { struct kvm_cpuid2 { __u32 nent; __u32 padding; - struct kvm_cpuid_entry2 entries[]; + __DECLARE_FLEX_ARRAY(struct kvm_cpuid_entry2, entries); }; /* for KVM_GET_PIT and KVM_SET_PIT */ @@ -398,7 +398,7 @@ struct kvm_xsave { * the contents of CPUID leaf 0xD on the host. */ __u32 region[1024]; - __u32 extra[]; + __DECLARE_FLEX_ARRAY(__u32, extra); }; #define KVM_MAX_XCRS 16 @@ -566,7 +566,7 @@ struct kvm_pmu_event_filter { __u32 fixed_counter_bitmap; __u32 flags; __u32 pad[4]; - __u64 events[]; + __DECLARE_FLEX_ARRAY(__u64, events); }; #define KVM_PMU_EVENT_ALLOW 0 diff --git a/include/uapi/linux/kvm.h b/include/uapi/linux/kvm.h index 80364d4dbebb..3f0d8d3c3daf 100644 --- a/include/uapi/linux/kvm.h +++ b/include/uapi/linux/kvm.h @@ -11,6 +11,7 @@ #include #include #include +#include #include #include @@ -542,7 +543,7 @@ struct kvm_coalesced_mmio { struct kvm_coalesced_mmio_ring { __u32 first, last; - struct kvm_coalesced_mmio coalesced_mmio[]; + __DECLARE_FLEX_ARRAY(struct kvm_coalesced_mmio, coalesced_mmio); }; #define KVM_COALESCED_MMIO_MAX \ @@ -592,7 +593,7 @@ struct kvm_clear_dirty_log { /* for KVM_SET_SIGNAL_MASK */ struct kvm_signal_mask { __u32 len; - __u8 sigset[]; + __DECLARE_FLEX_ARRAY(__u8, sigset); }; /* for KVM_TPR_ACCESS_REPORTING */ @@ -1051,7 +1052,7 @@ struct kvm_irq_routing_entry { struct kvm_irq_routing { __u32 nr; __u32 flags; - struct kvm_irq_routing_entry entries[]; + __DECLARE_FLEX_ARRAY(struct kvm_irq_routing_entry, entries); }; #define KVM_IRQFD_FLAG_DEASSIGN (1 << 0) @@ -1142,7 +1143,7 @@ struct kvm_dirty_tlb { struct kvm_reg_list { __u64 n; /* number of regs */ - __u64 reg[]; + __DECLARE_FLEX_ARRAY(__u64, reg); }; struct kvm_one_reg { @@ -1608,7 +1609,7 @@ struct kvm_stats_desc { #ifdef __KERNEL__ char name[KVM_STATS_NAME_SIZE]; #else - char name[]; + __DECLARE_FLEX_ARRAY(char, name); #endif };