Re: [PATCH Part1 RFC v2 03/20] x86/sev: Add support for hypervisor feature VMGEXIT

[Brijesh Singh]

On 5/11/21 5:01 AM, Borislav Petkov wrote:
> On Fri, Apr 30, 2021 at 07:15:59AM -0500, Brijesh Singh wrote:
>> Version 2 of GHCB specification introduced advertisement of a features
>> that are supported by the hypervisor. Define the GHCB MSR protocol and NAE
>> for the hypervisor feature request and query the feature during the GHCB
>> protocol negotitation. See the GHCB specification for more details.
>>
>> Signed-off-by: Brijesh Singh <brijesh.singh@xxxxxxx>
>> ---
>>  arch/x86/include/asm/sev-common.h | 17 +++++++++++++++++
>>  arch/x86/include/uapi/asm/svm.h   |  2 ++
>>  arch/x86/kernel/sev-shared.c      | 24 ++++++++++++++++++++++++
>>  3 files changed, 43 insertions(+)
>>
>> diff --git a/arch/x86/include/asm/sev-common.h b/arch/x86/include/asm/sev-common.h
>> index 9f1b66090a4c..8142e247d8da 100644
>> --- a/arch/x86/include/asm/sev-common.h
>> +++ b/arch/x86/include/asm/sev-common.h
>> @@ -51,6 +51,22 @@
>>  #define GHCB_MSR_AP_RESET_HOLD_RESULT_POS	12
>>  #define GHCB_MSR_AP_RESET_HOLD_RESULT_MASK	0xfffffffffffff
>>  
>> +/* GHCB Hypervisor Feature Request */
>> +#define GHCB_MSR_HV_FEATURES_REQ	0x080
>> +#define GHCB_MSR_HV_FEATURES_RESP	0x081
>> +#define GHCB_MSR_HV_FEATURES_POS	12
>> +#define GHCB_MSR_HV_FEATURES_MASK	0xfffffffffffffUL
>> +#define GHCB_MSR_HV_FEATURES_RESP_VAL(v)	\
>> +	(((v) >> GHCB_MSR_HV_FEATURES_POS) & GHCB_MSR_HV_FEATURES_MASK)
>> +
>> +#define GHCB_HV_FEATURES_SNP		BIT_ULL(0)
>> +#define GHCB_HV_FEATURES_SNP_AP_CREATION			\
>> +		(BIT_ULL(1) | GHCB_HV_FEATURES_SNP)
>> +#define GHCB_HV_FEATURES_SNP_RESTRICTED_INJECTION		\
>> +		(BIT_ULL(2) | GHCB_HV_FEATURES_SNP_AP_CREATION)
>> +#define GHCB_HV_FEATURES_SNP_RESTRICTED_INJECTION_TIMER		\
>> +		(BIT_ULL(3) | GHCB_HV_FEATURES_SNP_RESTRICTED_INJECTION)
> Please add those in the patches which use them - not in bulk here.
>
> And GHCB_HV_FEATURES_SNP_RESTRICTED_INJECTION_TIMER is a mouthfull and
> looks like BIOS code to me. But this is still the kernel, remember? :-)
>
> So let's do
>
> GHCB_MSR_HV_FT_*
>
> GHCB_SNP_AP_CREATION
> GHCB_SNP_RESTRICTED_INJ
> GHCB_SNP_RESTRICTED_INJ_TMR
>
> and so on so that we can all keep our sanity when reading that code.

I am fine with the reduced name, I just hope that "TMR" does not create
confusion with "Trusted Memory Region" documented in  SEV-ES firmware
specification. Since I am working on both guest and OVMF patches
simultaneously so its possible that I just worked on this code after
OVMF and used the same mouthful name ;)  I apologies for those nits.


>> +
>>  #define GHCB_MSR_TERM_REQ		0x100
>>  #define GHCB_MSR_TERM_REASON_SET_POS	12
>>  #define GHCB_MSR_TERM_REASON_SET_MASK	0xf
>> @@ -62,6 +78,7 @@
>>  
>>  #define GHCB_SEV_ES_REASON_GENERAL_REQUEST	0
>>  #define GHCB_SEV_ES_REASON_PROTOCOL_UNSUPPORTED	1
>> +#define GHCB_SEV_ES_REASON_SNP_UNSUPPORTED	2
> I remember asking for those to get shortened too
>
> GHCB_SEV_ES_GEN_REQ
> GHCB_SEV_ES_PROT_UNSUPPORTED
> GHCB_SEV_ES_SNP_UNSUPPORTED
>
> Perhaps in a prepatch?

Sure, I will send prepatch.


>>  #define GHCB_RESP_CODE(v)		((v) & GHCB_MSR_INFO_MASK)
>>  
>> diff --git a/arch/x86/include/uapi/asm/svm.h b/arch/x86/include/uapi/asm/svm.h
>> index 554f75fe013c..7fbc311e2de1 100644
>> --- a/arch/x86/include/uapi/asm/svm.h
>> +++ b/arch/x86/include/uapi/asm/svm.h
>> @@ -108,6 +108,7 @@
>>  #define SVM_VMGEXIT_AP_JUMP_TABLE		0x80000005
>>  #define SVM_VMGEXIT_SET_AP_JUMP_TABLE		0
>>  #define SVM_VMGEXIT_GET_AP_JUMP_TABLE		1
>> +#define SVM_VMGEXIT_HYPERVISOR_FEATURES		0x8000fffd
> SVM_VMGEXIT_HV_FT
>
> you get the idea.
>
>>  #define SVM_VMGEXIT_UNSUPPORTED_EVENT		0x8000ffff
>>  
>>  #define SVM_EXIT_ERR           -1
>> @@ -215,6 +216,7 @@
>>  	{ SVM_VMGEXIT_NMI_COMPLETE,	"vmgexit_nmi_complete" }, \
>>  	{ SVM_VMGEXIT_AP_HLT_LOOP,	"vmgexit_ap_hlt_loop" }, \
>>  	{ SVM_VMGEXIT_AP_JUMP_TABLE,	"vmgexit_ap_jump_table" }, \
>> +	{ SVM_VMGEXIT_HYPERVISOR_FEATURES,	"vmgexit_hypervisor_feature" }, \
>>  	{ SVM_EXIT_ERR,         "invalid_guest_state" }
>>  
>>  
>> diff --git a/arch/x86/kernel/sev-shared.c b/arch/x86/kernel/sev-shared.c
>> index 48a47540b85f..874f911837db 100644
>> --- a/arch/x86/kernel/sev-shared.c
>> +++ b/arch/x86/kernel/sev-shared.c
>> @@ -20,6 +20,7 @@
>>   * out when the .bss section is later cleared.
>>   */
>>  static u16 ghcb_version __section(".data") = 0;
>> +static u64 hv_features __section(".data") = 0;
> ERROR: do not initialise statics to 0
> #181: FILE: arch/x86/kernel/sev-shared.c:23:
> +static u64 hv_features __section(".data") = 0;
>
>>  static bool __init sev_es_check_cpu_features(void)
>>  {
>> @@ -49,6 +50,26 @@ static void __noreturn sev_es_terminate(unsigned int reason)
>>  		asm volatile("hlt\n" : : : "memory");
>>  }
>>  
>> +static bool ghcb_get_hv_features(void)
> Used only once here - no need for the ghcb_ prefix.
Noted.
>
>> +{
>> +	u64 val;
>> +
>> +	/* The hypervisor features are available from version 2 onward. */
>> +	if (ghcb_version < 2)
>> +		return true;
> 		return false;
> no?
>
> Also, this should be done differently:
>
> 	if (ghcb_version >= 2)
> 		get_hv_features();
>
> at the call site.

I can go with the change in the call site itself.


>
> Thx.
>