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x86/vdso: Provide vdso_data offset on vvar_page

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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
This commit is contained in:
Dmitry Safonov 2019-11-12 01:27:10 +00:00 committed by Thomas Gleixner
parent 660fd04f93
commit 64b302ab66
5 changed files with 17 additions and 9 deletions
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2
arch/x86/entry/vdso/vdso-layout.lds.S
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@ -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;

11
arch/x86/entry/vdso/vma.c
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@ -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

8
arch/x86/include/asm/vvar.h
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@ -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)

4
arch/x86/kernel/vmlinux.lds.S
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@ -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
/*

1
include/linux/time_namespace.h
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@ -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)
{