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

[Tom Lendacky]

On 11/8/23 02:21, Jeremi Piotrowski wrote:
> 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.

Ah, good catch. Let me work on getting the APM updated.

Thanks,
Tom

> Thanks,
> Jeremi