KVM: Add helper function for reading x86 segment registers

Acked-by: Petr Vorel <[email protected]>
Acked-by: Cyril Hrubis <[email protected]>
Signed-off-by: Martin Doucha <[email protected]>

Author: mdoucha

doc/kvm-test-api.txt

@@ -329,6 +329,10 @@ struct kvm_cpuid {
 struct kvm_cregs {
 	unsigned long cr0, cr2, cr3, cr4;
 };
+
+struct kvm_sregs {
+	uint16_t cs, ds, es, fs, gs, ss;
+};
 -------------------------------------------------------------------------------
 
 `struct page_table_entry_pae` is the page table entry structure for PAE and
@@ -370,6 +374,9 @@ Developer's Manual, Volume 3, Chapter 4 for explanation of the fields.
 - `void kvm_read_cregs(struct kvm_cregs *buf)` – Copies the current values
   of control registers to `buf`.
 
+- `void kvm_read_sregs(struct kvm_sregs *buf)` - Copies the current values
+  of segment registers to `buf`.
+
 - `uint64_t kvm_rdmsr(unsigned int msr)` – Returns the current value
   of model-specific register `msr`.
 

testcases/kernel/kvm/bootstrap_x86.S

@@ -197,6 +197,25 @@ kvm_read_cregs:
 	pop %edi
 	ret
 
+.global kvm_read_sregs
+kvm_read_sregs:
+	push %edi
+	mov 8(%esp), %edi
+	mov %cs, %ax
+	movw %ax, (%edi)
+	mov %ds, %ax
+	movw %ax, 2(%edi)
+	mov %es, %ax
+	movw %ax, 4(%edi)
+	mov %fs, %ax
+	movw %ax, 6(%edi)
+	mov %gs, %ax
+	movw %ax, 8(%edi)
+	mov %ss, %ax
+	movw %ax, 10(%edi)
+	pop %edi
+	ret
+
 handle_interrupt:
 	/* save CPU state */
 	push %ebp

testcases/kernel/kvm/bootstrap_x86_64.S

@@ -303,6 +303,22 @@ kvm_read_cregs:
 	mov %rax, 24(%rdi)
 	retq
 
+.global kvm_read_sregs
+kvm_read_sregs:
+	mov %cs, %ax
+	movw %ax, (%rdi)
+	mov %ds, %ax
+	movw %ax, 2(%rdi)
+	mov %es, %ax
+	movw %ax, 4(%rdi)
+	mov %fs, %ax
+	movw %ax, 6(%rdi)
+	mov %gs, %ax
+	movw %ax, 8(%rdi)
+	mov %ss, %ax
+	movw %ax, 10(%rdi)
+	retq
+
 handle_interrupt:
 	/* push CPU state */
 	push %rbp

testcases/kernel/kvm/include/kvm_x86.h

@@ -158,6 +158,10 @@ struct kvm_cregs {
 	unsigned long cr0, cr2, cr3, cr4;
 };
 
+struct kvm_sregs {
+	uint16_t cs, ds, es, fs, gs, ss;
+};
+
 extern struct page_table_entry_pae kvm_pagetable[];
 extern struct intr_descriptor kvm_idt[X86_INTR_COUNT];
 extern struct segment_descriptor kvm_gdt[KVM_GDT_SIZE];
@@ -178,6 +182,7 @@ unsigned int kvm_create_stack_descriptor(struct segment_descriptor *table,
 /* Functions for querying CPU info and status */
 void kvm_get_cpuid(unsigned int eax, unsigned int ecx, struct kvm_cpuid *buf);
 void kvm_read_cregs(struct kvm_cregs *buf);
+void kvm_read_sregs(struct kvm_sregs *buf);
 uint64_t kvm_rdmsr(unsigned int msr);
 void kvm_wrmsr(unsigned int msr, uint64_t value);