Re: [PATCH v10 06/50] x86/sev: Add the host SEV-SNP initialization support

[Jeremi Piotrowski]

On 07/11/2023 19:32, Tom Lendacky wrote:
> On 11/7/23 10:31, Borislav Petkov wrote:
>>
>> And the stuff that needs to happen once, needs to be called once too.
>>
>>> +
>>> +    return snp_get_rmptable_info(&rmp_base, &rmp_size);
>>> +}
>>> +
>>>   static void early_detect_mem_encrypt(struct cpuinfo_x86 *c)
>>>   {
>>>       u64 msr;
>>> @@ -659,6 +674,9 @@ static void early_detect_mem_encrypt(struct cpuinfo_x86 *c)
>>>           if (!(msr & MSR_K7_HWCR_SMMLOCK))
>>>               goto clear_sev;
>>>   +        if (cpu_has(c, X86_FEATURE_SEV_SNP) && !early_rmptable_check())
>>> +            goto clear_snp;
>>> +
>>>           return;
>>>     clear_all:
>>> @@ -666,6 +684,7 @@ static void early_detect_mem_encrypt(struct cpuinfo_x86 *c)
>>>   clear_sev:
>>>           setup_clear_cpu_cap(X86_FEATURE_SEV);
>>>           setup_clear_cpu_cap(X86_FEATURE_SEV_ES);
>>> +clear_snp:
>>>           setup_clear_cpu_cap(X86_FEATURE_SEV_SNP);
>>>       }
>>>   }
>>
>> ...
>>
>>> +bool snp_get_rmptable_info(u64 *start, u64 *len)
>>> +{
>>> +    u64 max_rmp_pfn, calc_rmp_sz, rmp_sz, rmp_base, rmp_end;
>>> +
>>> +    rdmsrl(MSR_AMD64_RMP_BASE, rmp_base);
>>> +    rdmsrl(MSR_AMD64_RMP_END, rmp_end);
>>> +
>>> +    if (!(rmp_base & RMP_ADDR_MASK) || !(rmp_end & RMP_ADDR_MASK)) {
>>> +        pr_err("Memory for the RMP table has not been reserved by BIOS\n");
>>> +        return false;
>>> +    }
>>
>> If you're masking off bits 0-12 above...
> 
> Because the RMP_END MSR, most specifically, has a default value of 0x1fff, where bits [12:0] are reserved. So to specifically check if the MSR has been set to a non-zero end value, the bit are masked off. However, ...
> 

Do you have a source for this? Because the APM vol. 2, table A.7 says the reset value of RMP_END is all zeros.

Thanks,
Jeremi