Re: [PATCH v9 06/24] virt: sev-guest: Simplify VMPCK and sequence number assignments

Nikunj A. Dadhania
2024-06-19T06:06:29Z

On 6/19/2024 2:57 AM, Tom Lendacky wrote:
> On 5/30/24 23:30, Nikunj A Dadhania wrote:
>> Preparatory patch to remove direct usage of VMPCK and message sequence
>> number in the SEV guest driver. Use arrays for the VM platform
>> communication key and message sequence number to simplify the function and
>> usage.
>>
>> Signed-off-by: Nikunj A Dadhania <nikunj@amd.com>
>
> One minor comment below, otherwise, for the general logic of using an array:
>
> Reviewed-by: Tom Lendacky <thomas.lendacky@amd.com>
>
>> ---
>> arch/x86/include/asm/sev.h | 12 ++++-------
>> drivers/virt/coco/sev-guest/sev-guest.c | 27 ++++---------------------
>> 2 files changed, 8 insertions(+), 31 deletions(-)
>>
>> diff --git a/arch/x86/include/asm/sev.h b/arch/x86/include/asm/sev.h
>> index dbf17e66d52a..d06b08f7043c 100644
>> --- a/arch/x86/include/asm/sev.h
>> +++ b/arch/x86/include/asm/sev.h
>> @@ -118,6 +118,8 @@ struct sev_guest_platform_data {
>> u64 secrets_gpa;
>> };
>>
>> +#define VMPCK_MAX_NUM 4
>> +
>> /*
>> * The secrets page contains 96-bytes of reserved field that can be used by
>> * the guest OS. The guest OS uses the area to save the message sequence
>> @@ -126,10 +128,7 @@ struct sev_guest_platform_data {
>> * See the GHCB spec section Secret page layout for the format for this area.
>> */
>> struct secrets_os_area {
>> - u32 msg_seqno_0;
>> - u32 msg_seqno_1;
>> - u32 msg_seqno_2;
>> - u32 msg_seqno_3;
>> + u32 msg_seqno[VMPCK_MAX_NUM];
>> u64 ap_jump_table_pa;
>> u8 rsvd[40];
>> u8 guest_usage[32];
>> @@ -145,10 +144,7 @@ struct snp_secrets_page {
>> u32 fms;
>> u32 rsvd2;
>> u8 gosvw[16];
>> - u8 vmpck0[VMPCK_KEY_LEN];
>> - u8 vmpck1[VMPCK_KEY_LEN];
>> - u8 vmpck2[VMPCK_KEY_LEN];
>> - u8 vmpck3[VMPCK_KEY_LEN];
>> + u8 vmpck[VMPCK_MAX_NUM][VMPCK_KEY_LEN];
>> struct secrets_os_area os_area;
>> u8 rsvd3[3840];
>> } __packed;
>> diff --git a/drivers/virt/coco/sev-guest/sev-guest.c b/drivers/virt/coco/sev-guest/sev-guest.c
>> index 5c0cbdad9fa2..a3c0b22d2e14 100644
>> --- a/drivers/virt/coco/sev-guest/sev-guest.c
>> +++ b/drivers/virt/coco/sev-guest/sev-guest.c
>> @@ -668,30 +668,11 @@ static const struct file_operations snp_guest_fops = {
>>
>> static u8 *get_vmpck(int id, struct snp_secrets_page *secrets, u32 **seqno)
>> {
>> - u8 *key = NULL;
>> -
>> - switch (id) {
>> - case 0:
>> - *seqno = &secrets->os_area.msg_seqno_0;
>> - key = secrets->vmpck0;
>> - break;
>> - case 1:
>> - *seqno = &secrets->os_area.msg_seqno_1;
>> - key = secrets->vmpck1;
>> - break;
>> - case 2:
>> - *seqno = &secrets->os_area.msg_seqno_2;
>> - key = secrets->vmpck2;
>> - break;
>> - case 3:
>> - *seqno = &secrets->os_area.msg_seqno_3;
>> - key = secrets->vmpck3;
>> - break;
>> - default:
>> - break;
>> - }
>> + if ((id + 1) > VMPCK_MAX_NUM)
>> + return NULL;
>
> This looks a bit confusing to me, because of the way it has to be
> written with the "+ 1". I wonder if something like the following would
> read better:
>
> switch (id) {
> case 0 ... 3:
> *seqno = &secrets->os_area.msg_seqno[id];
> return secrets->vmpck[id];
> default:
> return NULL;
> }
>
> Just my opinion, if others are fine with it, then that's fine.

I have separated patch 6 and 7 for better code review and modular changes.

The next patch simplifes this further to:

static inline u8 *get_vmpck(struct snp_guest_dev *snp_dev)
{
return snp_dev->secrets->vmpck[snp_dev->vmpck_id];
}

static bool assign_vmpck(struct snp_guest_dev *dev, unsigned int vmpck_id)
{
if ((vmpck_id + 1) > VMPCK_MAX_NUM)
return false;

dev->vmpck_id = vmpck_id;

return true;
}

Regards
Nikunj