KVM: selftests: Use vm->pa_bits to generate reserved PA bits

Use vm->pa_bits to generate the mask of physical address bits that are
reserved in page table entries.  vm->pa_bits is set when the VM is
created, i.e. it's guaranteed to be valid when populating page tables.

Signed-off-by: Sean Christopherson <seanjc@google.com>
Link: https://lore.kernel.org/r/20220614200707.3315957-24-seanjc@google.com

tools/testing/selftests/kvm/lib/x86_64/processor.c

@@ -221,16 +221,12 @@ static uint64_t *_vm_get_page_table_entry(struct kvm_vm *vm,
 	uint16_t index[4];
 	uint64_t *pml4e, *pdpe, *pde;
 	uint64_t *pte;
-	struct kvm_cpuid_entry2 *entry;
 	struct kvm_sregs sregs;
-	int max_phy_addr;
 	uint64_t rsvd_mask = 0;
 
-	entry = kvm_get_supported_cpuid_index(0x80000008, 0);
-	max_phy_addr = entry->eax & 0x000000ff;
 	/* Set the high bits in the reserved mask. */
-	if (max_phy_addr < 52)
-		rsvd_mask = GENMASK_ULL(51, max_phy_addr);
+	if (vm->pa_bits < 52)
+		rsvd_mask = GENMASK_ULL(51, vm->pa_bits);
 
 	/*
 	 * SDM vol 3, fig 4-11 "Formats of CR3 and Paging-Structure Entries