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SubjectRe: [PATCH v2] selftests: KVM: avoid failures due to reserved HyperTransport region
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On 12/9/21 22:47, Sean Christopherson wrote:
>> + /*
>> + * Otherwise it's at the top of the physical address
>> + * space, possibly reduced due to SME by bits 11:6 of
>> + * CPUID[0x8000001f].EBX.
>> + */
>> + eax = 0x80000008;
>> + cpuid(&eax, &ebx, &ecx, &edx);
>
> Should't this check 0x80000000.eax >= 0x80000008 first? Or do we just accept
> failure if family==0x17 and there's no 0x80000008? One paranoid option would be
> to use the pre-fam17 value, e.g.
>
> /* Before family 17h, the HyperTransport area is just below 1T. */
> ht_gfn = (1 << 28) - num_ht_pages;
> if (x86_family(eax) < 0x17)
> goto out;
>
> eax = 0x80000000;
> cpuid(&eax, &ebx, &ecx, &edx);
> max_ext_leaf = eax;
>
> /* Use the old, conservative value if MAXPHYADDR isn't enumerated. */
> if (max_ext_leaf < 0x80000008)
> goto out;

Yes, this works for me too. Though in practice I don't think any 64-bit
machine ever existed without 0x80000008 (you need it to decide what's a
canonical address and what isn't), so that would have to be a 32-bit
fam17h machine.

Paolo

> /* comment */
> eax = 0x80000008;
> cpuid(&eax, &ebx, &ecx, &edx);
> max_pfn = (1ULL << ((eax & 255) - vm->page_shift)) - 1;
> if (max_ext_leaf >= 0x8000001f) {
> <adjust>
> }
> ht_gfn = max_pfn - num_ht_pages;
> out:
> return min(max_gfn, ht_gfn - 1);
>
>> + max_pfn = (1ULL << ((eax & 255) - vm->page_shift)) - 1;
> LOL, "& 255", you just couldn't resist, huh? My version of Rami Code only goes
> up to 15.:-)
>

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