[kvm-unit-tests PATCH 2/5] x86: add a few functions for gdt manipulation

[Maxim Levitsky <mlevitsk@xxxxxxxxxx>]

Add a few functions that will be used to manipulate various
segment bases that are loaded via GDT.

Signed-off-by: Maxim Levitsky <mlevitsk@xxxxxxxxxx>
---
 lib/x86/desc.c | 39 ++++++++++++++++++++++++++++++++-------
 lib/x86/desc.h |  5 +++++
 2 files changed, 37 insertions(+), 7 deletions(-)

diff --git a/lib/x86/desc.c b/lib/x86/desc.c
index d054899c6..52e33f201 100644
--- a/lib/x86/desc.c
+++ b/lib/x86/desc.c
@@ -338,7 +338,7 @@ bool exception_rflags_rf(void)
 
 static char intr_alt_stack[4096];
 
-void set_gdt_entry(int sel, unsigned long base,  u32 limit, u8 type, u8 flags)
+void set_gdt_entry_base(int sel, unsigned long base)
 {
 	gdt_entry_t *entry = &gdt[sel >> 3];
 
@@ -347,10 +347,6 @@ void set_gdt_entry(int sel, unsigned long base,  u32 limit, u8 type, u8 flags)
 	entry->base2 = (base >> 16) & 0xFF;
 	entry->base3 = (base >> 24) & 0xFF;
 
-	/* Setup the descriptor limits, type and flags */
-	entry->limit1 = (limit & 0xFFFF);
-	entry->type_limit_flags = ((limit & 0xF0000) >> 8) | ((flags & 0xF0) << 8) | type;
-
 #ifdef __x86_64__
 	if (!entry->s) {
 		struct system_desc64 *entry16 = (struct system_desc64 *)entry;
@@ -360,6 +356,25 @@ void set_gdt_entry(int sel, unsigned long base,  u32 limit, u8 type, u8 flags)
 #endif
 }
 
+void set_gdt_entry(int sel, unsigned long base,  u32 limit, u8 type, u8 flags)
+{
+	gdt_entry_t *entry = &gdt[sel >> 3];
+
+	/* Setup the descriptor limits, type and flags */
+	entry->limit1 = (limit & 0xFFFF);
+	entry->type_limit_flags = ((limit & 0xF0000) >> 8) | ((flags & 0xF0) << 8) | type;
+	set_gdt_entry_base(sel, base);
+}
+
+void clear_tss_busy(int sel)
+{
+	gdt_entry_t *entry = &gdt[sel >> 3];
+
+	entry->type_limit_flags &= ~0xFF;
+	entry->type_limit_flags |= 0x89;
+}
+
+
 void load_gdt_tss(size_t tss_offset)
 {
 	lgdt(&gdt_descr);
@@ -483,14 +498,24 @@ void __set_exception_jmpbuf(jmp_buf *addr)
 	exception_jmpbuf = addr;
 }
 
-gdt_entry_t *get_tss_descr(void)
+gdt_entry_t *get_gdt_entry(u16 sel)
 {
 	struct descriptor_table_ptr gdt_ptr;
 	gdt_entry_t *gdt;
 
 	sgdt(&gdt_ptr);
 	gdt = (gdt_entry_t *)gdt_ptr.base;
-	return &gdt[str() / 8];
+	return &gdt[sel / 8];
+}
+
+gdt_entry_t *get_tss_descr(void)
+{
+	return get_gdt_entry(str());
+}
+
+gdt_entry_t *get_ldt_descr(void)
+{
+	return get_gdt_entry(sldt());
 }
 
 unsigned long get_gdt_entry_base(gdt_entry_t *entry)
diff --git a/lib/x86/desc.h b/lib/x86/desc.h
index 5349ea572..a50c8f61b 100644
--- a/lib/x86/desc.h
+++ b/lib/x86/desc.h
@@ -246,6 +246,8 @@ void set_idt_entry(int vec, void *addr, int dpl);
 void set_idt_sel(int vec, u16 sel);
 void set_idt_dpl(int vec, u16 dpl);
 void set_gdt_entry(int sel, unsigned long base, u32 limit, u8 access, u8 gran);
+void set_gdt_entry_base(int sel, unsigned long base);
+void clear_tss_busy(int sel);
 void load_gdt_tss(size_t tss_offset);
 void set_intr_alt_stack(int e, void *fn);
 void print_current_tss_info(void);
@@ -268,7 +270,10 @@ static inline void *get_idt_addr(idt_entry_t *entry)
 	return (void *)addr;
 }
 
+extern gdt_entry_t *get_gdt_entry(u16 sel);
 extern gdt_entry_t *get_tss_descr(void);
+gdt_entry_t *get_ldt_descr(void);
+
 extern unsigned long get_gdt_entry_base(gdt_entry_t *entry);
 extern unsigned long get_gdt_entry_limit(gdt_entry_t *entry);
 
-- 
2.26.3