linux-kernel - Re: [PATCH Part1 RFC v2 09/20] x86/sev: check SEV-SNP features support

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Date:   Thu, 20 May 2021 12:40:40 -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 09/20] x86/sev: check SEV-SNP features
 support


On 5/20/21 11:02 AM, Borislav Petkov wrote:
> On Fri, Apr 30, 2021 at 07:16:05AM -0500, Brijesh Singh wrote:
>> diff --git a/arch/x86/boot/compressed/sev.c b/arch/x86/boot/compressed/sev.c
>> index 6d9055427f37..7badbeb6cb95 100644
>> --- a/arch/x86/boot/compressed/sev.c
>> +++ b/arch/x86/boot/compressed/sev.c
>> @@ -25,6 +25,8 @@
>>  
>>  struct ghcb boot_ghcb_page __aligned(PAGE_SIZE);
>>  struct ghcb *boot_ghcb;
>> +static u64 sev_status_val;
> msr_sev_status should be more descriptive.
Noted.
>
>> +static bool sev_status_checked;
> You don't need this one - you can simply do
>
> 	if (!msr_sev_status)
> 		read the MSR.

Agreed.


>
>>  /*
>>   * Copy a version of this function here - insn-eval.c can't be used in
>> @@ -119,11 +121,30 @@ static enum es_result vc_read_mem(struct es_em_ctxt *ctxt,
>>  /* Include code for early handlers */
>>  #include "../../kernel/sev-shared.c"
>>  
>> +static inline bool sev_snp_enabled(void)
>> +{
>> +	unsigned long low, high;
>> +
>> +	if (!sev_status_checked) {
>> +		asm volatile("rdmsr\n"
>> +			     : "=a" (low), "=d" (high)
>> +			     : "c" (MSR_AMD64_SEV));
>> +		sev_status_val = (high << 32) | low;
>> +		sev_status_checked = true;
>> +	}
>> +
>> +	return sev_status_val & MSR_AMD64_SEV_SNP_ENABLED ? true : false;
> 	return msr_sev_status & MSR_AMD64_SEV_SNP_ENABLED;
>
> is enough.

Noted.


>> +}
>> +
>>  static bool early_setup_sev_es(void)
>>  {
>>  	if (!sev_es_negotiate_protocol())
>>  		sev_es_terminate(0, GHCB_SEV_ES_REASON_PROTOCOL_UNSUPPORTED);
>>  
>> +	/* If SEV-SNP is enabled then check if the hypervisor supports the SEV-SNP features. */
> 80 cols like the rest of this file pls.

Noted.


>
>> +	if (sev_snp_enabled() && !sev_snp_check_hypervisor_features())
>> +		sev_es_terminate(0, GHCB_SEV_ES_REASON_SNP_UNSUPPORTED);
>> +
>>  	if (set_page_decrypted((unsigned long)&boot_ghcb_page))
>>  		return false;
> Thx.
>