[PATCH] uml: fix page faults in SKAS3 mode.

I hadn't been running a SKAS3 host when testing the "uml: fix hang in TT mode
on fault" patch (commit 546fe1cbf91d4d62e3849517c31a2327c992e5c5), and I
didn't think enough to the missing trap_no in SKAS3 mode.

In fact, the resulting kernel doesn't work at all in SKAS3 mode.

Signed-off-by: Paolo 'Blaisorblade' Giarrusso <[e-mail]>
Signed-off-by: Andrew Morton <[e-mail]>
Signed-off-by: Linus Torvalds <[e-mail]>

arch/um/include/sysdep-i386/sigcontext.h

···
 #ifndef __SYS_SIGCONTEXT_I386_H
 #define __SYS_SIGCONTEXT_I386_H
 
+#include "uml-config.h"
 #include <sysdep/sc.h>
 
 #define IP_RESTART_SYSCALL(ip) ((ip) -= 2)
···
 #define SC_START_SYSCALL(sc) do SC_EAX(sc) = -ENOSYS; while(0)
 
 /* This is Page Fault */
-#define SEGV_IS_FIXABLE(fi) ((fi)->trap_no == 14)
+#define SEGV_IS_FIXABLE(fi)	((fi)->trap_no == 14)
+
+/* SKAS3 has no trap_no on i386, but get_skas_faultinfo() sets it to 0. */
+#ifdef UML_CONFIG_MODE_SKAS
+#define SEGV_MAYBE_FIXABLE(fi)	((fi)->trap_no == 0 && ptrace_faultinfo)
+#else
+#define SEGV_MAYBE_FIXABLE(fi)	0
+#endif
 
 extern unsigned long *sc_sigmask(void *sc_ptr);
 extern int sc_get_fpregs(unsigned long buf, void *sc_ptr);

arch/um/include/sysdep-x86_64/sigcontext.h

···
 #define SC_START_SYSCALL(sc) do SC_RAX(sc) = -ENOSYS; while(0)
 
 /* This is Page Fault */
-#define SEGV_IS_FIXABLE(fi) ((fi)->trap_no == 14)
+#define SEGV_IS_FIXABLE(fi)	((fi)->trap_no == 14)
+
+/* No broken SKAS API, which doesn't pass trap_no, here. */
+#define SEGV_MAYBE_FIXABLE(fi)	0
 
 extern unsigned long *sc_sigmask(void *sc_ptr);
 

arch/um/kernel/trap_kern.c

···
 #include "mconsole_kern.h"
 #include "mem.h"
 #include "mem_kern.h"
+#ifdef CONFIG_MODE_SKAS
+#include "skas.h"
+#endif
 
 /* Note this is constrained to return 0, -EFAULT, -EACCESS, -ENOMEM by segv(). */
 int handle_page_fault(unsigned long address, unsigned long ip, 
···
 	else if(current->mm == NULL)
 		panic("Segfault with no mm");
 
-	if (SEGV_IS_FIXABLE(&fi))
+	if (SEGV_IS_FIXABLE(&fi) || SEGV_MAYBE_FIXABLE(&fi))
 		err = handle_page_fault(address, ip, is_write, is_user, &si.si_code);
 	else {
 		err = -EFAULT;