On Thu, Dec 09, 2021, Paolo Bonzini wrote:
> +unsigned long vm_compute_max_gfn(struct kvm_vm *vm)
> +{
> + const unsigned long num_ht_pages = 12 << 18; /* 12 GiB */
> + unsigned long ht_gfn, max_gfn, max_pfn;
> + uint32_t eax, ebx, ecx, edx;
> +
> + max_gfn = (1ULL << (vm->pa_bits - vm->page_shift)) - 1;
> +
> + /* Avoid reserved HyperTransport region on AMD processors. */
> + eax = ecx = 0;
> + cpuid(&eax, &ebx, &ecx, &edx);
> + if (ebx != X86EMUL_CPUID_VENDOR_AuthenticAMD_ebx ||
> + ecx != X86EMUL_CPUID_VENDOR_AuthenticAMD_ecx ||
> + edx != X86EMUL_CPUID_VENDOR_AuthenticAMD_edx)
> + return max_gfn;
> +
> + /* On parts with <40 physical address bits, the area is fully hidden */
> + if (vm->pa_bits < 40)
> + return max_gfn;
> +
> + eax = 1;
> + cpuid(&eax, &ebx, &ecx, &edx);
> + if (x86_family(eax) < 0x17) {
> + /* Before family 17h, the HyperTransport area is just below 1T. */
> + ht_gfn = (1 << 28) - num_ht_pages;
> + } else {
> + /*
> + * 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;
/* 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. :-)
