x86/vdso: Provide vdso_data offset on vvar_page

VDSO support for time namespaces needs to set up a page with the same
layout as VVAR. That timens page will be placed on position of VVAR page
inside namespace. That page has vdso_data->seq set to 1 to enforce
the slow path and vdso_data->clock_mode set to VCLOCK_TIMENS to enforce
the time namespace handling path.

To prepare the time namespace page the kernel needs to know the vdso_data
offset.  Provide arch_get_vdso_data() helper for locating vdso_data on VVAR
page.

Co-developed-by: Andrei Vagin <avagin@openvz.org>
Signed-off-by: Andrei Vagin <avagin@openvz.org>
Signed-off-by: Dmitry Safonov <dima@arista.com>
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Link: https://lore.kernel.org/r/20191112012724.250792-22-dima@arista.com

5 files changed, 17 insertions, 9 deletions

diff --git a/arch/x86/entry/vdso/vdso-layout.lds.S b/arch/x86/entry/vdso/vdso-layout.lds.S
index 93c6dc7812d0..2330daad67c3 100644
--- a/arch/x86/entry/vdso/vdso-layout.lds.S
+++ b/arch/x86/entry/vdso/vdso-layout.lds.S
@@ -21,9 +21,7 @@ SECTIONS
 
 	/* Place all vvars at the offsets in asm/vvar.h. */
 #define EMIT_VVAR(name, offset) vvar_ ## name = vvar_page + offset;
-#define __VVAR_KERNEL_LDS
 #include <asm/vvar.h>
-#undef __VVAR_KERNEL_LDS
 #undef EMIT_VVAR
 
 	pvclock_page = vvar_start + PAGE_SIZE;
diff --git a/arch/x86/entry/vdso/vma.c b/arch/x86/entry/vdso/vma.c
index 76cbe54e0c39..04e3498c6c41 100644
--- a/arch/x86/entry/vdso/vma.c
+++ b/arch/x86/entry/vdso/vma.c
@@ -24,6 +24,17 @@
 #include <asm/cpufeature.h>
 #include <clocksource/hyperv_timer.h>
 
+#undef _ASM_X86_VVAR_H
+#define EMIT_VVAR(name, offset)	\
+	const size_t name ## _offset = offset;
+#include <asm/vvar.h>
+
+struct vdso_data *arch_get_vdso_data(void *vvar_page)
+{
+	return (struct vdso_data *)(vvar_page + _vdso_data_offset);
+}
+#undef EMIT_VVAR
+
 #if defined(CONFIG_X86_64)
 unsigned int __read_mostly vdso64_enabled = 1;
 #endif
diff --git a/arch/x86/include/asm/vvar.h b/arch/x86/include/asm/vvar.h
index 32f5d9a0b90e..ff2de3025388 100644
--- a/arch/x86/include/asm/vvar.h
+++ b/arch/x86/include/asm/vvar.h
@@ -19,10 +19,10 @@
 #ifndef _ASM_X86_VVAR_H
 #define _ASM_X86_VVAR_H
 
-#if defined(__VVAR_KERNEL_LDS)
-
-/* The kernel linker script defines its own magic to put vvars in the
- * right place.
+#ifdef EMIT_VVAR
+/*
+ * EMIT_VVAR() is used by the kernel linker script to put vvars in the
+ * right place. Also, it's used by kernel code to import offsets values.
  */
 #define DECLARE_VVAR(offset, type, name) \
 	EMIT_VVAR(name, offset)
diff --git a/arch/x86/kernel/vmlinux.lds.S b/arch/x86/kernel/vmlinux.lds.S
index 3a1a819da137..e3296aa028fe 100644
--- a/arch/x86/kernel/vmlinux.lds.S
+++ b/arch/x86/kernel/vmlinux.lds.S
@@ -193,12 +193,10 @@ SECTIONS
 		__vvar_beginning_hack = .;
 
 		/* Place all vvars at the offsets in asm/vvar.h. */
-#define EMIT_VVAR(name, offset) 			\
+#define EMIT_VVAR(name, offset)				\
 		. = __vvar_beginning_hack + offset;	\
 		*(.vvar_ ## name)
-#define __VVAR_KERNEL_LDS
 #include <asm/vvar.h>
-#undef __VVAR_KERNEL_LDS
 #undef EMIT_VVAR
 
 		/*
diff --git a/include/linux/time_namespace.h b/include/linux/time_namespace.h
index 34ee110b5c35..063a343d1d78 100644
--- a/include/linux/time_namespace.h
+++ b/include/linux/time_namespace.h
@@ -39,6 +39,7 @@ struct time_namespace *copy_time_ns(unsigned long flags,
 				    struct time_namespace *old_ns);
 void free_time_ns(struct kref *kref);
 int timens_on_fork(struct nsproxy *nsproxy, struct task_struct *tsk);
+struct vdso_data *arch_get_vdso_data(void *vvar_page);
 
 static inline void put_time_ns(struct time_namespace *ns)
 {