linux-kernel - Re: [PATCH] nvme-tcp: Fix implicit padding in struct nvme_tcp_term

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Message-ID: <CADUfDZocrTZq2MPKFFNuJc5yBabG48EiEURwn7-t2UBuVZxCWg@mail.gmail.com>
Date:   Mon, 20 Mar 2023 08:34:38 -0700
From:   Caleb Sander <csander@...estorage.com>
To:     Geert Uytterhoeven <geert@...ux-m68k.org>
Cc:     Keith Busch <kbusch@...nel.org>, Jens Axboe <axboe@...com>,
        Christoph Hellwig <hch@....de>,
        Sagi Grimberg <sagi@...mberg.me>,
        Arnd Bergmann <arnd@...db.de>, linux-nvme@...ts.infradead.org,
        linux-m68k@...ts.linux-m68k.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH] nvme-tcp: Fix implicit padding in struct nvme_tcp_term_pdu

The nvme_tcp_term_pdu definition needs to be updated anyways to match
the spec. FEI is at offset 10, so it isn't 4-byte-aligned. I think we
have gotten away with this so far because the NVMe/TCP driver never
sends H2CTermReq and doesn't interpret C2HTermReq.
Mirroring numdl/numdu in nvme_get_log_page_command, the definition
should look something like:
struct nvme_tcp_term_pdu {
        struct nvme_tcp_hdr hdr;
        __le16 fes;
        __le16 feil;
        __le16 feiu;
        __u8 rsvd[10];
};

Best,
Caleb

On Mon, Mar 20, 2023 at 4:29 AM Geert Uytterhoeven <geert@...ux-m68k.org> wrote:
>
> On m68k:
>
>     drivers/nvme/host/tcp.c: In function ‘nvme_tcp_init_module’:
>     include/linux/compiler_types.h:397:38: error: call to ‘__compiletime_assert_723’ declared with attribute error: BUILD_BUG_ON failed: sizeof(struct nvme_tcp_term_pdu) != 24
>
> Indeed, on m68k the minimum alignment is 2 bytes, not 4 bytes, thus
> triggering the check added in commit 7e87965d3807ab1f ("nvme-tcp: add
> nvme-tcp pdu size build protection"), and indicating that NVMe over
> Fabrics TCP on m68k must be incompatible with other platforms.
>
> Fix this by adding explicit padding.
>
> Fixes: fc221d05447aa6db ("nvme-tcp: Add protocol header")
> Signed-off-by: Geert Uytterhoeven <geert@...ux-m68k.org>
> ---
>  include/linux/nvme-tcp.h | 1 +
>  1 file changed, 1 insertion(+)
>
> diff --git a/include/linux/nvme-tcp.h b/include/linux/nvme-tcp.h
> index 75470159a194d97f..ba8f82672e39730f 100644
> --- a/include/linux/nvme-tcp.h
> +++ b/include/linux/nvme-tcp.h
> @@ -115,6 +115,7 @@ struct nvme_tcp_icresp_pdu {
>  struct nvme_tcp_term_pdu {
>         struct nvme_tcp_hdr     hdr;
>         __le16                  fes;
> +       __u8                    rsvd2[2];
>         __le32                  fei;
>         __u8                    rsvd[8];
>  };
> --
> 2.34.1
>
>