linux-kernel - Re: [PATCH v10 06/24] virt: sev-guest: Simplify VMPCK and sequence number assignments

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Message-ID: <97f596b5-5ced-867f-5246-03345d06bed6@amd.com>
Date: Fri, 28 Jun 2024 09:55:28 +0530
From: "Nikunj A. Dadhania" <nikunj@....com>
To: Borislav Petkov <bp@...en8.de>
Cc: linux-kernel@...r.kernel.org, thomas.lendacky@....com, x86@...nel.org,
 kvm@...r.kernel.org, mingo@...hat.com, tglx@...utronix.de,
 dave.hansen@...ux.intel.com, pgonda@...gle.com, seanjc@...gle.com,
 pbonzini@...hat.com
Subject: Re: [PATCH v10 06/24] virt: sev-guest: Simplify VMPCK and sequence
 number assignments



On 6/25/2024 10:34 PM, Borislav Petkov wrote:
> On Fri, Jun 21, 2024 at 06:08:45PM +0530, Nikunj A Dadhania wrote:
>> Preparatory patch to remove direct usage of VMPCK and message sequence
> 
> "Prepare the code for removing... "
> 
> From Documentation/process/submitting-patches.rst:
> 
> "Describe your changes in imperative mood, e.g. "make xyzzy do frotz"
> instead of "[This patch] makes xyzzy do frotz" or "[I] changed xyzzy
> to do frotz", as if you are giving orders to the codebase to change
> its behaviour."
> 
>> number in the SEV guest driver.
> 
> remove, because...?

SNP guest driver currently is accessing os_area and VMPCK of secrets page.
Prepare the code for removing direct usage of these and later provide clean
accessor API to 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@....com>
>> Reviewed-by: Tom Lendacky <thomas.lendacky@....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 2ac899adcbf6..473760208764 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];
>> @@ -214,10 +213,7 @@ 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 vmsa_tweak_bitmap[64];
>> diff --git a/drivers/virt/coco/sev-guest/sev-guest.c b/drivers/virt/coco/sev-guest/sev-guest.c
>> index 61e190ecfa3a..a5602c84769f 100644
>> --- a/drivers/virt/coco/sev-guest/sev-guest.c
>> +++ b/drivers/virt/coco/sev-guest/sev-guest.c
>> @@ -678,30 +678,11 @@ static const struct file_operations snp_guest_fops = {
>>  
>>  static u8 *get_vmpck(int id, struct snp_secrets_page *secrets, u32 **seqno)
> 
> Why is this a separate function when it is used only once?

This will later be moved and an API provided, will be used from SEV guest driver 
and Secure TSC code. I had that as a single patch, you had suggested to split the
a separate patch.

> 
>>  {
>> -	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 < VMPCK_MAX_NUM))
>> +		return NULL;
> 
> Or
> 
> 	if (id >= VMPCK_MAX_NUM)
> 		return NULL;
> 
> ?

Sure

> 
> Also that id needs to be unsigned as it is an array index.
> 

Yes, changed in following patch 07/24. Do you want me to pull those changes to this patch ?

Regards,
Nikunj