[tip: timers/core] x86/vdso: Provide vdso_data offset on vvar_page

[tip-bot2 for Dmitry Safonov]

The following commit has been merged into the timers/core branch of tip:

Commit-ID:     9bec781deb4d5f23ee6346873805058bd0f6c88b
Gitweb:        https://git.kernel.org/tip/9bec781deb4d5f23ee6346873805058bd0f6c88b
Author:        Dmitry Safonov <dima@xxxxxxxxxx>
AuthorDate:    Tue, 12 Nov 2019 01:27:10 
Committer:     Thomas Gleixner <tglx@xxxxxxxxxxxxx>
CommitterDate: Mon, 13 Jan 2020 08:10:55 +01:00

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@xxxxxxxxxx>
Signed-off-by: Andrei Vagin <avagin@xxxxxxxxxx>
Signed-off-by: Dmitry Safonov <dima@xxxxxxxxxx>
Signed-off-by: Thomas Gleixner <tglx@xxxxxxxxxxxxx>
Link: https://lore.kernel.org/r/20191112012724.250792-22-dima@xxxxxxxxxx

---
 arch/x86/entry/vdso/vdso-layout.lds.S |  2 --
 arch/x86/entry/vdso/vma.c             | 11 +++++++++++
 arch/x86/include/asm/vvar.h           |  8 ++++----
 arch/x86/kernel/vmlinux.lds.S         |  4 +---
 include/linux/time_namespace.h        |  1 +
 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 93c6dc7..2330daa 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 76cbe54..04e3498 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 32f5d9a..ff2de30 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 3a1a819..e3296aa 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 34ee110..063a343 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)
 {