Re: [PATCH] drm/amdgpu: Pack VF2PF ucode_info entries to keep struct size 1KB

["Lazar, Lijo" <lijo.lazar@amd.com>]

On 13-Mar-26 7:46 PM, Zhang, Bokun wrote:
> [AMD Official Use Only - AMD Internal Distribution Only]
> 
> Hey there,
>      Thank you for the change, but this header is already packed.
> *#pragma pack(push, 1) *// PF2VF / VF2PF data areas are byte packed
> ...
> *#pragma pack(pop) *// Restore previous packing option
>      Please check these 2 macros.
>      The header mush also match across platforms, so we prefer do not 
> change it.
> 

A related discussion - 
https://lists.freedesktop.org/archives/amd-gfx/2023-June/094818.html

<quoted from related discussion>

https://lore.kernel.org/linux-sparse/CAHk-=wi7jGZ+bVbt-UfXOkpEQdHzF3Z2HBjkGdjh8q4dvPPGWQ@mail.gmail.com/

Thanks,
Lijo

> Thanks!
> 
> ------------------------------------------------------------------------
> *From:* Srinivasan Shanmugam <srinivasan.shanmugam@amd.com>
> *Sent:* Thursday, March 12, 2026 8:51 AM
> *To:* Koenig, Christian <Christian.Koenig@amd.com>; Deucher, Alexander 
> <Alexander.Deucher@amd.com>
> *Cc:* amd-gfx@lists.freedesktop.org <amd-gfx@lists.freedesktop.org>; 
> SHANMUGAM, SRINIVASAN <SRINIVASAN.SHANMUGAM@amd.com>; Zhang, Bokun 
> <Bokun.Zhang@amd.com>; Liu, Monk <Monk.Liu@amd.com>
> *Subject:* [PATCH] drm/amdgpu: Pack VF2PF ucode_info entries to keep 
> struct size 1KB
> 
> The VF2PF mailbox structure must be exactly 1KB, which is enforced by
> a compile-time static assertion.
> 
> The ucode_info array currently uses a small struct containing:
> 
>    uint8_t id
>    uint32_t version
> 
> Without explicit packing, the compiler may insert padding after the
> uint8_t field so that the uint32_t field starts at a 4-byte aligned
> address. For example, the layout may become:
> 
>    id (1 byte) + 3 bytes padding + version (4 bytes)
> 
> which makes the struct 8 bytes instead of the expected 5 bytes.
> 
> Since the structure contains multiple ucode_info entries, this padding
> can increase the total structure size beyond 1024 bytes and cause the
> 1KB size check to fail.
> 
> Define the ucode_info entry as a packed struct to ensure each entry
> remains 5 bytes and the VF2PF mailbox structure stays exactly 1KB.
> 
> Fixes the below:
> drivers/gpu/drm/amd/amdgpu/amdgv_sriovmsg.h:510:49: error: static 
> assertion failed: "amd_sriov_msg_vf2pf_info must be 1 KB"
> 
> Fixes: 1721bc1b2afa ("drm/amdgpu: Update VF2PF interface")
> Cc: Bokun Zhang <Bokun.Zhang@amd.com>
> Cc: Monk Liu <monk.liu@amd.com>
> Cc: Alex Deucher <alexander.deucher@amd.com>
> Cc: Christian König <christian.koenig@amd.com>
> Signed-off-by: Srinivasan Shanmugam <srinivasan.shanmugam@amd.com>
> ---
>   drivers/gpu/drm/amd/amdgpu/amdgv_sriovmsg.h | 10 ++++++----
>   1 file changed, 6 insertions(+), 4 deletions(-)
> 
> diff --git a/drivers/gpu/drm/amd/amdgpu/amdgv_sriovmsg.h b/drivers/gpu/ 
> drm/amd/amdgpu/amdgv_sriovmsg.h
> index 847cfd1fd004..31fc54111519 100644
> --- a/drivers/gpu/drm/amd/amdgpu/amdgv_sriovmsg.h
> +++ b/drivers/gpu/drm/amd/amdgpu/amdgv_sriovmsg.h
> @@ -328,6 +328,11 @@ struct amd_sriov_msg_vf2pf_info_header {
>           uint32_t reserved[2];
>   };
> 
> +struct amd_sriov_msg_ucode_info {
> +       u8 id;
> +       u32 version;
> +} __packed;
> +
>   #define AMD_SRIOV_MSG_VF2PF_INFO_FILLED_SIZE (73)
>   struct amd_sriov_msg_vf2pf_info {
>           /* header contains size and version */
> @@ -367,10 +372,7 @@ struct amd_sriov_msg_vf2pf_info {
>           uint32_t fb_vis_size;
>           uint32_t fb_size;
>           /* guest ucode data, each one is 1.25 Dword */
> -       struct {
> -               uint8_t id;
> -               uint32_t version;
> -       } ucode_info[AMD_SRIOV_MSG_RESERVE_UCODE];
> +       struct amd_sriov_msg_ucode_info 
> ucode_info[AMD_SRIOV_MSG_RESERVE_UCODE];
>           uint64_t dummy_page_addr;
>           /* FB allocated for guest MES to record UQ info */
>           uint64_t mes_info_addr;
> --
> 2.34.1
>