[PATCH] uml: check for differences in host support
If running on a host not supporting TLS (for instance 2.4) we should report
that cleanly to the user, instead of printing not comprehensible "error 5" for
that.
Additionally, i386 and x86_64 support different ranges for
user_desc->entry_number, and we must account for that; we couldn't pass
ourselves -1 because we need to override previously existing TLS descriptors
which glibc has possibly set, so test at startup the range to use.
x86 and x86_64 existing ranges are hardcoded.
Signed-off-by: Paolo 'Blaisorblade' Giarrusso <blaisorblade@yahoo.it>
Acked-by: Jeff Dike <jdike@addtoit.com>
Signed-off-by: Andrew Morton <akpm@osdl.org>
Signed-off-by: Linus Torvalds <torvalds@osdl.org>
diff --git a/arch/um/include/os.h b/arch/um/include/os.h
index 1b780b5..f88856c 100644
--- a/arch/um/include/os.h
+++ b/arch/um/include/os.h
@@ -173,6 +173,7 @@
extern void os_early_checks(void);
extern int can_do_skas(void);
extern void os_check_bugs(void);
+extern void check_host_supports_tls(int *supports_tls, int *tls_min);
/* Make sure they are clear when running in TT mode. Required by
* SEGV_MAYBE_FIXABLE */
diff --git a/arch/um/include/sysdep-i386/tls.h b/arch/um/include/sysdep-i386/tls.h
index 938f953..918fd3c 100644
--- a/arch/um/include/sysdep-i386/tls.h
+++ b/arch/um/include/sysdep-i386/tls.h
@@ -25,4 +25,8 @@
typedef struct user_desc user_desc_t;
# endif /* __KERNEL__ */
+
+#define GDT_ENTRY_TLS_MIN_I386 6
+#define GDT_ENTRY_TLS_MIN_X86_64 12
+
#endif /* _SYSDEP_TLS_H */
diff --git a/arch/um/include/user_util.h b/arch/um/include/user_util.h
index 615f2f0..fe0c29b 100644
--- a/arch/um/include/user_util.h
+++ b/arch/um/include/user_util.h
@@ -8,6 +8,9 @@
#include "sysdep/ptrace.h"
+/* Copied from kernel.h */
+#define ARRAY_SIZE(x) (sizeof(x) / sizeof((x)[0]))
+
#define CATCH_EINTR(expr) while ((errno = 0, ((expr) < 0)) && (errno == EINTR))
extern int mode_tt;
diff --git a/arch/um/os-Linux/sys-i386/Makefile b/arch/um/os-Linux/sys-i386/Makefile
index 340ef26..b321361 100644
--- a/arch/um/os-Linux/sys-i386/Makefile
+++ b/arch/um/os-Linux/sys-i386/Makefile
@@ -3,7 +3,7 @@
# Licensed under the GPL
#
-obj-$(CONFIG_MODE_SKAS) = registers.o
+obj-$(CONFIG_MODE_SKAS) = registers.o tls.o
USER_OBJS := $(obj-y)
diff --git a/arch/um/os-Linux/sys-i386/tls.c b/arch/um/os-Linux/sys-i386/tls.c
new file mode 100644
index 0000000..ba21f0e
--- /dev/null
+++ b/arch/um/os-Linux/sys-i386/tls.c
@@ -0,0 +1,33 @@
+#include <linux/unistd.h>
+#include "sysdep/tls.h"
+#include "user_util.h"
+
+static _syscall1(int, get_thread_area, user_desc_t *, u_info);
+
+/* Checks whether host supports TLS, and sets *tls_min according to the value
+ * valid on the host.
+ * i386 host have it == 6; x86_64 host have it == 12, for i386 emulation. */
+void check_host_supports_tls(int *supports_tls, int *tls_min) {
+ /* Values for x86 and x86_64.*/
+ int val[] = {GDT_ENTRY_TLS_MIN_I386, GDT_ENTRY_TLS_MIN_X86_64};
+ int i;
+
+ for (i = 0; i < ARRAY_SIZE(val); i++) {
+ user_desc_t info;
+ info.entry_number = val[i];
+
+ if (get_thread_area(&info) == 0) {
+ *tls_min = val[i];
+ *supports_tls = 1;
+ return;
+ } else {
+ if (errno == EINVAL)
+ continue;
+ else if (errno == ENOSYS)
+ *supports_tls = 0;
+ return;
+ }
+ }
+
+ *supports_tls = 0;
+}
diff --git a/arch/um/os-Linux/tls.c b/arch/um/os-Linux/tls.c
index 642db55..9cb09a4 100644
--- a/arch/um/os-Linux/tls.c
+++ b/arch/um/os-Linux/tls.c
@@ -48,8 +48,8 @@
#ifdef UML_CONFIG_MODE_TT
#include "linux/unistd.h"
-_syscall1(int, get_thread_area, user_desc_t *, u_info);
-_syscall1(int, set_thread_area, user_desc_t *, u_info);
+static _syscall1(int, get_thread_area, user_desc_t *, u_info);
+static _syscall1(int, set_thread_area, user_desc_t *, u_info);
int do_set_thread_area_tt(user_desc_t *info)
{
diff --git a/arch/um/sys-i386/tls.c b/arch/um/sys-i386/tls.c
index 2251654..a3188e8 100644
--- a/arch/um/sys-i386/tls.c
+++ b/arch/um/sys-i386/tls.c
@@ -24,6 +24,10 @@
#include "skas.h"
#endif
+/* If needed we can detect when it's uninitialized. */
+static int host_supports_tls = -1;
+int host_gdt_entry_tls_min = -1;
+
#ifdef CONFIG_MODE_SKAS
int do_set_thread_area_skas(struct user_desc *info)
{
@@ -157,11 +161,20 @@
}
}
-/* This in SKAS0 does not need to be used, since we have different host
- * processes. Nor will this need to be used when we'll add support to the host
+/* In SKAS0 mode, currently, multiple guest threads sharing the same ->mm have a
+ * common host process. So this is needed in SKAS0 too.
+ *
+ * However, if each thread had a different host process (and this was discussed
+ * for SMP support) this won't be needed.
+ *
+ * And this will not need be used when (and if) we'll add support to the host
* SKAS patch. */
+
int arch_switch_tls_skas(struct task_struct *from, struct task_struct *to)
{
+ if (!host_supports_tls)
+ return 0;
+
/* We have no need whatsoever to switch TLS for kernel threads; beyond
* that, that would also result in us calling os_set_thread_area with
* userspace_pid[cpu] == 0, which gives an error. */
@@ -173,6 +186,9 @@
int arch_switch_tls_tt(struct task_struct *from, struct task_struct *to)
{
+ if (!host_supports_tls)
+ return 0;
+
if (needs_TLS_update(to))
return load_TLS(0, to);
@@ -256,6 +272,9 @@
struct user_desc info;
int idx, ret;
+ if (!host_supports_tls)
+ return -ENOSYS;
+
if (copy_from_user(&info, user_desc, sizeof(info)))
return -EFAULT;
@@ -287,6 +306,9 @@
{
struct user_desc info;
+ if (!host_supports_tls)
+ return -EIO;
+
if (copy_from_user(&info, user_desc, sizeof(info)))
return -EFAULT;
@@ -298,6 +320,9 @@
struct user_desc info;
int idx, ret;
+ if (!host_supports_tls)
+ return -ENOSYS;
+
if (get_user(idx, &user_desc->entry_number))
return -EFAULT;
@@ -321,6 +346,9 @@
struct user_desc info;
int ret;
+ if (!host_supports_tls)
+ return -EIO;
+
ret = get_tls_entry(child, &info, idx);
if (ret < 0)
goto out;
@@ -331,3 +359,26 @@
return ret;
}
+
+/* XXX: This part is probably common to i386 and x86-64. Don't create a common
+ * file for now, do that when implementing x86-64 support.*/
+static int __init __setup_host_supports_tls(void) {
+ check_host_supports_tls(&host_supports_tls, &host_gdt_entry_tls_min);
+ if (host_supports_tls) {
+ printk(KERN_INFO "Host TLS support detected\n");
+ printk(KERN_INFO "Detected host type: ");
+ switch (host_gdt_entry_tls_min) {
+ case GDT_ENTRY_TLS_MIN_I386:
+ printk("i386\n");
+ break;
+ case GDT_ENTRY_TLS_MIN_X86_64:
+ printk("x86_64\n");
+ break;
+ }
+ } else
+ printk(KERN_ERR " Host TLS support NOT detected! "
+ "TLS support inside UML will not work\n");
+ return 1;
+}
+
+__initcall(__setup_host_supports_tls);
diff --git a/include/asm-um/segment.h b/include/asm-um/segment.h
index 4877545..45183fc 100644
--- a/include/asm-um/segment.h
+++ b/include/asm-um/segment.h
@@ -1,6 +1,10 @@
#ifndef __UM_SEGMENT_H
#define __UM_SEGMENT_H
-#include "asm/arch/segment.h"
+extern int host_gdt_entry_tls_min;
+
+#define GDT_ENTRY_TLS_ENTRIES 3
+#define GDT_ENTRY_TLS_MIN host_gdt_entry_tls_min
+#define GDT_ENTRY_TLS_MAX (GDT_ENTRY_TLS_MIN + GDT_ENTRY_TLS_ENTRIES - 1)
#endif