Test that error code is pushed on exception's task stack.

If exception with error code is handled by task gate, error code should
be pushed to new task stack.
Signed-off-by: Gleb Natapov <gleb@redhat.com>
Signed-off-by: Marcelo Tosatti <mtosatti@redhat.com>

x86/taskswitch2.c

@@ -3,6 +3,7 @@
 #include "apic-defs.h"
 #include "apic.h"
 #include "processor.h"
+#include "vm.h"
 
 #define xstr(s) str(s)
 #define str(s) #s
@@ -10,6 +11,9 @@
 static volatile int test_count;
 static volatile unsigned int test_divider;
 
+static char *fault_addr;
+static ulong fault_phys;
+
 static int g_fail;
 static int g_tests;
 
@@ -66,6 +70,27 @@ start:
 	goto start;
 }
 
+void do_pf_tss(ulong *error_code)
+{
+	printf("PF task is running %x %x\n", error_code, *(ulong*)error_code);
+	print_current_tss_info();
+	if (*(ulong*)error_code == 0x2) /* write access, not present */
+		test_count++;
+	install_pte(phys_to_virt(read_cr3()), 1, fault_addr,
+		    fault_phys | PTE_PRESENT | PTE_WRITE, 0);
+}
+
+extern void pf_tss(void);
+
+asm (
+	"pf_tss: \n\t"
+	"push %esp \n\t"
+	"call do_pf_tss \n\t"
+	"add $4, %esp \n\t"
+	"iret\n\t"
+	"jmp pf_tss\n\t"
+    );
+
 static void jmp_tss(void)
 {
 start:
@@ -92,6 +117,7 @@ int main()
 {
 	unsigned int res;
 
+	setup_vm();
 	setup_idt();
 	setup_gdt();
 	setup_tss32();
@@ -156,6 +182,19 @@ int main()
 	printf("Return from int 3\n");
 	report("BP exeption", test_count == 1);
 
+	/*
+	 * test that PF triggers task gate and error code is placed on
+	 * exception task's stack
+	 */
+	fault_addr = alloc_vpage();
+	fault_phys = (ulong)virt_to_phys(alloc_page());
+	test_count = 0;
+	set_intr_task_gate(14, pf_tss);
+	printf("Access unmapped page\n");
+	*fault_addr = 0;
+	printf("Return from pf tss\n");
+	report("PF exeption", test_count == 1);
+
 	/* test that calling a task by lcall works */
 	test_count = 0;
 	set_intr_task_gate(0, irq_tss);