linux-kernel - Re: [PATCH Part1 RFC v2 06/20] x86/sev: Define SNP guest request NAE events

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Date:   Tue, 18 May 2021 08:42:44 -0500
From:   Brijesh Singh <brijesh.singh@....com>
To:     Borislav Petkov <bp@...en8.de>
Cc:     brijesh.singh@....com, x86@...nel.org,
        linux-kernel@...r.kernel.org, kvm@...r.kernel.org,
        tglx@...utronix.de, jroedel@...e.de, thomas.lendacky@....com,
        pbonzini@...hat.com, mingo@...hat.com, dave.hansen@...el.com,
        rientjes@...gle.com, seanjc@...gle.com, peterz@...radead.org,
        hpa@...or.com, tony.luck@...el.com
Subject: Re: [PATCH Part1 RFC v2 06/20] x86/sev: Define SNP guest request NAE
 events


On 5/18/21 5:45 AM, Borislav Petkov wrote:
> On Fri, Apr 30, 2021 at 07:16:02AM -0500, Brijesh Singh wrote:
>> Version 2 of the GHCB specification added the support for SNP guest
>> request NAE events. The SEV-SNP guests will use this event to request
>> the attestation report. See the GHCB specification for more details.
>>
>> Signed-off-by: Brijesh Singh <brijesh.singh@....com>
>> ---
>>  arch/x86/include/uapi/asm/svm.h | 4 ++++
>>  1 file changed, 4 insertions(+)
>>
>> diff --git a/arch/x86/include/uapi/asm/svm.h b/arch/x86/include/uapi/asm/svm.h
>> index f7bf12cad58c..7a45aa284530 100644
>> --- a/arch/x86/include/uapi/asm/svm.h
>> +++ b/arch/x86/include/uapi/asm/svm.h
>> @@ -109,6 +109,8 @@
>>  #define SVM_VMGEXIT_SET_AP_JUMP_TABLE		0
>>  #define SVM_VMGEXIT_GET_AP_JUMP_TABLE		1
>>  #define SVM_VMGEXIT_SNP_PAGE_STATE_CHANGE	0x80000010
>> +#define SVM_VMGEXIT_SNP_GUEST_REQUEST		0x80000011
>> +#define SVM_VMGEXIT_SNP_EXT_GUEST_REQUEST	0x80000012
> Why does this need the "VMGEXIT" *and* "SNP" prefixes?
>
> Why not simply:
>
> SVM_VMGEXIT_GUEST_REQ
> SVM_VMGEXIT_EXT_GUEST_REQ
>
> like the rest of the VMGEXIT defines in there?

This VMGEXIT is optional and is available only when the SNP feature is
advertised through HV_FEATURE VMGEXIT. The GHCB specification spells it
with the "SNP" prefix" to distinguish it from others. The other
"VMGEXIT's" defined in this file are available for both the SNP and ES
guests, so we don't need any prefixes.


>
>>  #define SVM_VMGEXIT_HYPERVISOR_FEATURES		0x8000fffd
>>  #define SVM_VMGEXIT_UNSUPPORTED_EVENT		0x8000ffff
>>  
>> @@ -218,6 +220,8 @@
>>  	{ SVM_VMGEXIT_AP_HLT_LOOP,	"vmgexit_ap_hlt_loop" }, \
>>  	{ SVM_VMGEXIT_AP_JUMP_TABLE,	"vmgexit_ap_jump_table" }, \
>>  	{ SVM_VMGEXIT_SNP_PAGE_STATE_CHANGE,	"vmgexit_page_state_change" }, \
>> +	{ SVM_VMGEXIT_SNP_GUEST_REQUEST,	"vmgexit_snp_guest_request" }, \
>> +	{ SVM_VMGEXIT_SNP_EXT_GUEST_REQUEST,	"vmgexit_snp_extended_guest_request" }, \
>>  	{ SVM_VMGEXIT_HYPERVISOR_FEATURES,	"vmgexit_hypervisor_feature" }, \
>>  	{ SVM_EXIT_ERR,         "invalid_guest_state" }
> Ditto.
>