On 4/16/2024 2:36 PM, Borislav Petkov wrote:
> On Tue, Apr 16, 2024 at 11:27:24AM +0530, Nikunj A. Dadhania wrote:
>>> Why does that snp_get_os_area_msg_seqno() returns a pointer when you
>>> deref it here again?
>>>
>>> A function which returns a sequence number should return that number
>>> - not a pointer to it.
>>>
>>> Which then makes that u32 *os_area_msg_seqno redundant and you can use
>>> the function directly.
>>>
>>> IOW:
>>>
>>> static inline u32 snp_get_os_area_msg_seqno(struct snp_guest_dev *snp_dev)
>>> {
>>> return snp_dev->layout->os_area.msg_seqno_0 + snp_dev->vmpck_id;
>>
>> This patch removes setting of layour page in snp_dev structure.
>
> So?
* Instead of using snp_dev->layout, we will need to access it using platform_data->layout structure.
* Below will give incorrect value of sequence number, it will get VMPCK_0's sequence number and will add vmpck_id to that. Will work by fluke for VMPCK=0, but will fail for all other keys.
return snp_dev->layout->os_area.msg_seqno_0 + snp_dev->vmpck_id;
struct secrets_os_area {
...
u32 msg_seqno_0;
u32 msg_seqno_1;
u32 msg_seqno_2;
u32 msg_seqno_3;
...
}
* I am using vmpck_id to index to correct msg_seqno_*
Changing this to
struct secrets_os_area {
...
u32 msg_seqno[VMPCK_MAX_NUM];
...
}
>
>> static inline u32 snp_get_os_area_msg_seqno(struct snp_guest_dev *snp_dev)
>> {
>> if (!platform_data)
>> return NULL;
>>
>> return *(&platform_data->layout->os_area.msg_seqno_0 + vmpck_id);
>> }
>
> What?!
I can change the secrets_os_area like below to simplify things:
struct secrets_os_area {
...
u32 msg_seqno[VMPCK_MAX_NUM];
...
}
static inline u32 snp_get_os_area_msg_seqno(struct snp_guest_dev *snp_dev)
{
if (!platform_data)
return NULL;
return platform_data->layout->os_area.msg_seqno[snp_dev->vmpck_id];
}
>
> This snp_get_os_area_msg_seqno() is a new function added by this patch.
>
>> I had a getter for getting the os_area_msg_seqno pointer, probably not
>> a good function name.
>
> Probably you need to go back to the drawing board and think about how
> this thing should look like.
>
>>> Do you see the imbalance in the APIs?
>>
>> The msg_seqno should only be incremented by 2 (always), that was the reason to avoid a setter.
>
> And what's wrong with the setter doing the incrementation so that
> callers can't even get it wrong?
Are you suggesting that setter should always increment by 2?
static inline u32 snp_set_os_area_msg_seqno(struct snp_guest_dev *snp_dev)
{
...
os_area.msg_seqno[snp_dev->vmpck_id] += 2;
...
}
>
> It sounds to me like you should redesign this sequence number handling
> in a *separate* patch.
Sure, let me rethink and will post it as separate patch.
Regards
Nikunj
