Re: [PATCH] KVM: Remove subtle "struct kvm_stats_desc" pseudo-overlay

From: Christian Borntraeger <borntraeger@linux.ibm.com>
To: Sean Christopherson <seanjc@google.com>,
	Marc Zyngier <maz@kernel.org>, Oliver Upton <oupton@kernel.org>,
	Tianrui Zhao <zhaotianrui@loongson.cn>,
	Bibo Mao <maobibo@loongson.cn>,
	Huacai Chen <chenhuacai@kernel.org>,
	Madhavan Srinivasan <maddy@linux.ibm.com>,
	Anup Patel <anup@brainfault.org>, Paul Walmsley <pjw@kernel.org>,
	Palmer Dabbelt <palmer@dabbelt.com>,
	Albert Ou <aou@eecs.berkeley.edu>,
	Janosch Frank <frankja@linux.ibm.com>,
	Claudio Imbrenda <imbrenda@linux.ibm.com>,
	Paolo Bonzini <pbonzini@redhat.com>
Cc: linux-arm-kernel@lists.infradead.org, kvmarm@lists.linux.dev,
	kvm@vger.kernel.org, loongarch@lists.linux.dev,
	linux-mips@vger.kernel.org, linuxppc-dev@lists.ozlabs.org,
	kvm-riscv@lists.infradead.org, linux-riscv@lists.infradead.org,
	linux-kernel@vger.kernel.org,
	"Gustavo A . R . Silva" <gustavoars@kernel.org>
Subject: Re: [PATCH] KVM: Remove subtle "struct kvm_stats_desc" pseudo-overlay
Date: Mon, 8 Dec 2025 11:32:27 +0100	[thread overview]
Message-ID: <8f1c1b9e-2743-4326-9a6f-754885ae90f4@linux.ibm.com> (raw)
In-Reply-To: <20251205232655.445294-1-seanjc@google.com>

Am 06.12.25 um 00:26 schrieb Sean Christopherson:
> Remove KVM's internal pseudo-overlay of kvm_stats_desc, which subtly
> aliases the flexible name[] in the uAPI definition with a fixed-size array
> of the same name.  The unusual embedded structure results in compiler
> warnings due to -Wflex-array-member-not-at-end, and also necessitates an
> extra level of dereferencing in KVM.  To avoid the "overlay", define the
> uAPI structure to have a fixed-size name when building for the kernel.
> 
> Opportunistically clean up the indentation for the stats macros, and
> replace spaces with tabs.
> 
> No functional change intended.
> 
> Reported-by: Gustavo A. R. Silva <gustavoars@kernel.org>
> Closes: https://lore.kernel.org/all/aPfNKRpLfhmhYqfP@kspp
> Signed-off-by: Sean Christopherson <seanjc@google.com>

Acked-by: Christian Borntraeger <borntraeger@linux.ibm.com>
[..]

> --- a/include/uapi/linux/kvm.h
> +++ b/include/uapi/linux/kvm.h
> @@ -14,6 +14,10 @@
>   #include <linux/ioctl.h>
>   #include <asm/kvm.h>
>   
> +#ifdef __KERNEL__
> +#include <linux/kvm_types.h>
> +#endif
> +
>   #define KVM_API_VERSION 12
>   
>   /*
> @@ -1579,7 +1583,11 @@ struct kvm_stats_desc {
>   	__u16 size;
>   	__u32 offset;
>   	__u32 bucket_size;
> +#ifdef __KERNEL__
> +	char name[KVM_STATS_NAME_SIZE];
> +#else
>   	char name[];
> +#endif
>   };

Not sure if we need a comment here or not. Maybe git blame is good enough.

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