linux-kernel - Re: [PATCH RFC 15/13] gpio: virtio: reorder fields to reduce struct padding

lists.openwall.net		lists / announce owl-users owl-dev john-users john-dev passwdqc-users yescrypt popa3d-users / oss-security kernel-hardening musl sabotage tlsify passwords / crypt-dev xvendor / Bugtraq Full-Disclosure linux-kernel linux-netdev linux-ext4 linux-hardening linux-cve-announce PHC
Open Source and information security mailing list archives

Hash Suite: Windows password security audit tool. GUI, reports in PDF.

[<prev] [next>] [<thread-prev] [thread-next>] [day] [month] [year] [list]

Message-ID: <CAMRc=MfWX5CZ6GL0ph1g-KupBS3gaztk=VxTnfC1QwUvQmuZrg@mail.gmail.com>
Date: Fri, 2 Jan 2026 12:47:04 +0000
From: Bartosz Golaszewski <brgl@...nel.org>
To: "Michael S. Tsirkin" <mst@...hat.com>
Cc: linux-kernel@...r.kernel.org, Cong Wang <xiyou.wangcong@...il.com>, 
	Jonathan Corbet <corbet@....net>, Olivia Mackall <olivia@...enic.com>, 
	Herbert Xu <herbert@...dor.apana.org.au>, Jason Wang <jasowang@...hat.com>, 
	Paolo Bonzini <pbonzini@...hat.com>, Stefan Hajnoczi <stefanha@...hat.com>, 
	Eugenio Pérez <eperezma@...hat.com>, 
	"James E.J. Bottomley" <James.Bottomley@...senpartnership.com>, 
	"Martin K. Petersen" <martin.petersen@...cle.com>, Gerd Hoffmann <kraxel@...hat.com>, 
	Xuan Zhuo <xuanzhuo@...ux.alibaba.com>, Marek Szyprowski <m.szyprowski@...sung.com>, 
	Robin Murphy <robin.murphy@....com>, Stefano Garzarella <sgarzare@...hat.com>, 
	"David S. Miller" <davem@...emloft.net>, Eric Dumazet <edumazet@...gle.com>, 
	Jakub Kicinski <kuba@...nel.org>, Paolo Abeni <pabeni@...hat.com>, Simon Horman <horms@...nel.org>, 
	Petr Tesarik <ptesarik@...e.com>, Leon Romanovsky <leon@...nel.org>, Jason Gunthorpe <jgg@...pe.ca>, 
	linux-doc@...r.kernel.org, linux-crypto@...r.kernel.org, 
	virtualization@...ts.linux.dev, linux-scsi@...r.kernel.org, 
	iommu@...ts.linux.dev, kvm@...r.kernel.org, netdev@...r.kernel.org, 
	"Enrico Weigelt, metux IT consult" <info@...ux.net>, Viresh Kumar <vireshk@...nel.org>, Linus Walleij <linusw@...nel.org>, 
	Bartosz Golaszewski <brgl@...nel.org>, linux-gpio@...r.kernel.org
Subject: Re: [PATCH RFC 15/13] gpio: virtio: reorder fields to reduce struct padding

On Tue, 30 Dec 2025 17:40:33 +0100, "Michael S. Tsirkin" <mst@...hat.com> said:
> Reorder struct virtio_gpio_line fields to place the DMA buffers (req/res)
> last. This eliminates the need for __dma_from_device_aligned_end padding
> after the DMA buffer, since struct tail padding naturally protects it,
> making the struct a bit smaller.
>
> Size reduction estimation when ARCH_DMA_MINALIGN=128:
> - request is 8 bytes
> - response is 2 bytes
> - removing _end saves up to 128-6=122 bytes padding to align rxlen field
>
> Signed-off-by: Michael S. Tsirkin <mst@...hat.com>
> ---
>  drivers/gpio/gpio-virtio.c | 5 ++---
>  1 file changed, 2 insertions(+), 3 deletions(-)
>
> diff --git a/drivers/gpio/gpio-virtio.c b/drivers/gpio/gpio-virtio.c
> index 32b578b46df8..8b30a94e4625 100644
> --- a/drivers/gpio/gpio-virtio.c
> +++ b/drivers/gpio/gpio-virtio.c
> @@ -26,12 +26,11 @@ struct virtio_gpio_line {
>  	struct mutex lock; /* Protects line operation */
>  	struct completion completion;
>
> +	unsigned int rxlen;
> +
>  	__dma_from_device_aligned_begin
>  	struct virtio_gpio_request req;
>  	struct virtio_gpio_response res;
> -
> -	__dma_from_device_aligned_end
> -	unsigned int rxlen;
>  };
>
>  struct vgpio_irq_line {
> --
> MST
>
>

Acked-by: Bartosz Golaszewski <bartosz.golaszewski@....qualcomm.com>