um: remove auxiliary FP registers

We do not need the extra save/restore of the FP registers when getting
the fault information. This was originally added in commit 2f56debd77a8
("uml: fix FP register corruption") but at that time the code was not
saving/restoring the FP registers when switching to userspace. This was
fixed in commit fbfe9c847edf ("um: Save FPU registers between task
switches") and since then the auxiliary registers have not been useful.

Signed-off-by: Benjamin Berg <[e-mail]>
Link: https://patch.msgid.link/[e-mail]
Signed-off-by: Johannes Berg <[e-mail]>

arch/um/include/asm/thread_info.h

···
 	int			preempt_count;  /* 0 => preemptable,
 						   <0 => BUG */
 	struct thread_info	*real_thread;    /* Points to non-IRQ stack */
-	unsigned long aux_fp_regs[FP_SIZE];	/* auxiliary fp_regs to save/restore
-						   them out-of-band */
 };
 
 #define INIT_THREAD_INFO(tsk)			\

arch/um/include/shared/os.h

···
 /* skas/process.c */
 extern int is_skas_winch(int pid, int fd, void *data);
 extern int start_userspace(unsigned long stub_stack);
-extern void userspace(struct uml_pt_regs *regs, unsigned long *aux_fp_regs);
+extern void userspace(struct uml_pt_regs *regs);
 extern void new_thread(void *stack, jmp_buf *buf, void (*handler)(void));
 extern void switch_threads(jmp_buf *me, jmp_buf *you);
 extern int start_idle_thread(void *stack, jmp_buf *switch_buf);

arch/um/kernel/process.c

···
 	 * callback returns only if the kernel thread execs a process
 	 */
 	fn(arg);
-	userspace(&current->thread.regs.regs, current_thread_info()->aux_fp_regs);
+	userspace(&current->thread.regs.regs);
 }
 
 /* Called magically, see new_thread_handler above */
···
 
 	current->thread.prev_sched = NULL;
 
-	userspace(&current->thread.regs.regs, current_thread_info()->aux_fp_regs);
+	userspace(&current->thread.regs.regs);
 }
 
 int copy_thread(struct task_struct * p, const struct kernel_clone_args *args)

arch/um/os-Linux/skas/process.c

···
 
 extern unsigned long current_stub_stack(void);
 
-static void get_skas_faultinfo(int pid, struct faultinfo *fi, unsigned long *aux_fp_regs)
+static void get_skas_faultinfo(int pid, struct faultinfo *fi)
 {
 	int err;
 
-	err = get_fp_registers(pid, aux_fp_regs);
-	if (err < 0) {
-		printk(UM_KERN_ERR "save_fp_registers returned %d\n",
-		       err);
-		fatal_sigsegv();
-	}
 	err = ptrace(PTRACE_CONT, pid, 0, SIGSEGV);
 	if (err) {
 		printk(UM_KERN_ERR "Failed to continue stub, pid = %d, "
···
 	 * the stub stack page. We just have to copy it.
 	 */
 	memcpy(fi, (void *)current_stub_stack(), sizeof(*fi));
-
-	err = put_fp_registers(pid, aux_fp_regs);
-	if (err < 0) {
-		printk(UM_KERN_ERR "put_fp_registers returned %d\n",
-		       err);
-		fatal_sigsegv();
-	}
 }
 
-static void handle_segv(int pid, struct uml_pt_regs *regs, unsigned long *aux_fp_regs)
+static void handle_segv(int pid, struct uml_pt_regs *regs)
 {
-	get_skas_faultinfo(pid, &regs->faultinfo, aux_fp_regs);
+	get_skas_faultinfo(pid, &regs->faultinfo);
 	segv(regs->faultinfo, 0, 1, NULL);
 }
 
···
 	return err;
 }
 
-void userspace(struct uml_pt_regs *regs, unsigned long *aux_fp_regs)
+void userspace(struct uml_pt_regs *regs)
 {
 	int err, status, op, pid = userspace_pid[0];
 	siginfo_t si;
···
 			case SIGSEGV:
 				if (PTRACE_FULL_FAULTINFO) {
 					get_skas_faultinfo(pid,
-							   &regs->faultinfo, aux_fp_regs);
+							   &regs->faultinfo);
 					(*sig_info[SIGSEGV])(SIGSEGV, (struct siginfo *)&si,
 							     regs);
 				}
-				else handle_segv(pid, regs, aux_fp_regs);
+				else handle_segv(pid, regs);
 				break;
 			case SIGTRAP + 0x80:
 				handle_trap(pid, regs);