KVM: selftests: Init x86's segments during VM creation

Initialize x86's various segments in the GDT during creation of relevant
VMs instead of waiting until vCPUs come along.  Re-installing the segments
for every vCPU is both wasteful and confusing, as is installing KERNEL_DS
multiple times; NOT installing KERNEL_DS for GS is icing on the cake.

Reviewed-by: Ackerley Tng <ackerleytng@google.com>
Link: https://lore.kernel.org/r/20240314232637.2538648-18-seanjc@google.com
Signed-off-by: Sean Christopherson <seanjc@google.com>

Author: sean-jc

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

@@ -439,24 +439,7 @@ static void kvm_seg_fill_gdt_64bit(struct kvm_vm *vm, struct kvm_segment *segp)
 		desc->base3 = segp->base >> 32;
 }
 
-
-/*
- * Set Long Mode Flat Kernel Code Segment
- *
- * Input Args:
- *   vm - VM whose GDT is being filled, or NULL to only write segp
- *   selector - selector value
- *
- * Output Args:
- *   segp - Pointer to KVM segment
- *
- * Return: None
- *
- * Sets up the KVM segment pointed to by @segp, to be a code segment
- * with the selector value given by @selector.
- */
-static void kvm_seg_set_kernel_code_64bit(struct kvm_vm *vm, uint16_t selector,
-	struct kvm_segment *segp)
+static void kvm_seg_set_kernel_code_64bit(uint16_t selector, struct kvm_segment *segp)
 {
 	memset(segp, 0, sizeof(*segp));
 	segp->selector = selector;
@@ -468,27 +451,9 @@ static void kvm_seg_set_kernel_code_64bit(struct kvm_vm *vm, uint16_t selector,
 	segp->g = true;
 	segp->l = true;
 	segp->present = 1;
-	if (vm)
-		kvm_seg_fill_gdt_64bit(vm, segp);
 }
 
-/*
- * Set Long Mode Flat Kernel Data Segment
- *
- * Input Args:
- *   vm - VM whose GDT is being filled, or NULL to only write segp
- *   selector - selector value
- *
- * Output Args:
- *   segp - Pointer to KVM segment
- *
- * Return: None
- *
- * Sets up the KVM segment pointed to by @segp, to be a data segment
- * with the selector value given by @selector.
- */
-static void kvm_seg_set_kernel_data_64bit(struct kvm_vm *vm, uint16_t selector,
-	struct kvm_segment *segp)
+static void kvm_seg_set_kernel_data_64bit(uint16_t selector, struct kvm_segment *segp)
 {
 	memset(segp, 0, sizeof(*segp));
 	segp->selector = selector;
@@ -499,8 +464,6 @@ static void kvm_seg_set_kernel_data_64bit(struct kvm_vm *vm, uint16_t selector,
 					  */
 	segp->g = true;
 	segp->present = true;
-	if (vm)
-		kvm_seg_fill_gdt_64bit(vm, segp);
 }
 
 vm_paddr_t addr_arch_gva2gpa(struct kvm_vm *vm, vm_vaddr_t gva)
@@ -518,16 +481,15 @@ vm_paddr_t addr_arch_gva2gpa(struct kvm_vm *vm, vm_vaddr_t gva)
 	return vm_untag_gpa(vm, PTE_GET_PA(*pte)) | (gva & ~HUGEPAGE_MASK(level));
 }
 
-static void kvm_setup_tss_64bit(struct kvm_vm *vm, struct kvm_segment *segp,
-				int selector)
+static void kvm_seg_set_tss_64bit(vm_vaddr_t base, struct kvm_segment *segp,
+				  int selector)
 {
 	memset(segp, 0, sizeof(*segp));
-	segp->base = vm->arch.tss;
+	segp->base = base;
 	segp->limit = 0x67;
 	segp->selector = selector;
 	segp->type = 0xb;
 	segp->present = 1;
-	kvm_seg_fill_gdt_64bit(vm, segp);
 }
 
 static void vcpu_init_sregs(struct kvm_vm *vm, struct kvm_vcpu *vcpu)
@@ -549,11 +511,11 @@ static void vcpu_init_sregs(struct kvm_vm *vm, struct kvm_vcpu *vcpu)
 	sregs.efer |= (EFER_LME | EFER_LMA | EFER_NX);
 
 	kvm_seg_set_unusable(&sregs.ldt);
-	kvm_seg_set_kernel_code_64bit(vm, KERNEL_CS, &sregs.cs);
-	kvm_seg_set_kernel_data_64bit(vm, KERNEL_DS, &sregs.ds);
-	kvm_seg_set_kernel_data_64bit(vm, KERNEL_DS, &sregs.es);
-	kvm_seg_set_kernel_data_64bit(NULL, KERNEL_DS, &sregs.gs);
-	kvm_setup_tss_64bit(vm, &sregs.tr, KERNEL_TSS);
+	kvm_seg_set_kernel_code_64bit(KERNEL_CS, &sregs.cs);
+	kvm_seg_set_kernel_data_64bit(KERNEL_DS, &sregs.ds);
+	kvm_seg_set_kernel_data_64bit(KERNEL_DS, &sregs.es);
+	kvm_seg_set_kernel_data_64bit(KERNEL_DS, &sregs.gs);
+	kvm_seg_set_tss_64bit(vm->arch.tss, &sregs.tr, KERNEL_TSS);
 
 	sregs.cr3 = vm->pgd;
 	vcpu_sregs_set(vcpu, &sregs);
@@ -613,6 +575,7 @@ void route_exception(struct ex_regs *regs)
 static void vm_init_descriptor_tables(struct kvm_vm *vm)
 {
 	extern void *idt_handlers;
+	struct kvm_segment seg;
 	int i;
 
 	vm->arch.gdt = __vm_vaddr_alloc_page(vm, MEM_REGION_DATA);
@@ -625,6 +588,15 @@ static void vm_init_descriptor_tables(struct kvm_vm *vm)
 		set_idt_entry(vm, i, (unsigned long)(&idt_handlers)[i], 0, KERNEL_CS);
 
 	*(vm_vaddr_t *)addr_gva2hva(vm, (vm_vaddr_t)(&exception_handlers)) = vm->handlers;
+
+	kvm_seg_set_kernel_code_64bit(KERNEL_CS, &seg);
+	kvm_seg_fill_gdt_64bit(vm, &seg);
+
+	kvm_seg_set_kernel_data_64bit(KERNEL_DS, &seg);
+	kvm_seg_fill_gdt_64bit(vm, &seg);
+
+	kvm_seg_set_tss_64bit(vm->arch.tss, &seg, KERNEL_TSS);
+	kvm_seg_fill_gdt_64bit(vm, &seg);
 }
 
 void vm_install_exception_handler(struct kvm_vm *vm, int vector,