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

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Message-ID: <fd2e2729-98cb-4406-af99-b8f3dd23bb13@amd.com>
Date: Tue, 25 Mar 2025 18:05:57 +0530
From: "Gupta, Akshay" <Akshay.Gupta@....com>
To: Arnd Bergmann <arnd@...db.de>, linux-hwmon@...r.kernel.org,
 linux-kernel@...r.kernel.org
Cc: Guenter Roeck <linux@...ck-us.net>,
 Greg Kroah-Hartman <gregkh@...uxfoundation.org>, shyam-sundar.s-k@....com,
 gautham.shenoy@....com, Mario Limonciello <mario.limonciello@....com>,
 naveenkrishna.chatradhi@....com, anand.umarji@....com
Subject: Re: [PATCH v6 08/11] misc: amd-sbi: Add support for CPUID protocol


On 3/24/2025 8:59 PM, Arnd Bergmann wrote:
> Caution: This message originated from an External Source. Use proper caution when opening attachments, clicking links, or responding.
>
>
> 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.