Re: [PATCH v6 08/11] misc: amd-sbi: Add support for CPUID protocol

[Gupta, Akshay]

On 3/24/2025 8:59 PM, Arnd Bergmann wrote:
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>
> On Mon, Mar 24, 2025, at 15:58, Akshay Gupta wrote:
>
> >   struct apml_message {
> >        /*
> >         * [0]...[3] mailbox 32bit input
> > +      *           cpuid,
> > +      * [4][5] cpuid: thread
> > +      * [6] cpuid: ext function & read eax/ebx or ecx/edx
> > +      *      [7:0] -> bits [7:4] -> ext function &
> > +      *      bit [0] read eax/ebx or ecx/edx
> >         * [7] read/write functionality
> >         */
> >        union {
> > +             __u64 cpu_msr_in;
> >                __u32 mb_in[2];
> >                __u8 reg_in[8];
> >        } data_in;
> This changes the alignment of the structure and makes
> it incompatible between 32-bit and 64-bit userspace
> when there is an odd number of 32-bit words in it.
>
>        Arnd
Ack, I will add explicit padding of __u32 padding[2] in the end in the 
structure.