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. :-)