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Message-Id: <20190729215758.28405-26-dima@arista.com>
Date: Mon, 29 Jul 2019 22:57:07 +0100
From: Dmitry Safonov <dima@...sta.com>
To: linux-kernel@...r.kernel.org
Cc: Dmitry Safonov <0x7f454c46@...il.com>,
Dmitry Safonov <dima@...sta.com>,
Adrian Reber <adrian@...as.de>,
Andrei Vagin <avagin@...nvz.org>,
Andy Lutomirski <luto@...nel.org>,
Arnd Bergmann <arnd@...db.de>,
Christian Brauner <christian.brauner@...ntu.com>,
Cyrill Gorcunov <gorcunov@...nvz.org>,
"Eric W. Biederman" <ebiederm@...ssion.com>,
"H. Peter Anvin" <hpa@...or.com>, Ingo Molnar <mingo@...hat.com>,
Jann Horn <jannh@...gle.com>, Jeff Dike <jdike@...toit.com>,
Oleg Nesterov <oleg@...hat.com>,
Pavel Emelyanov <xemul@...tuozzo.com>,
Shuah Khan <shuah@...nel.org>,
Thomas Gleixner <tglx@...utronix.de>,
Vincenzo Frascino <vincenzo.frascino@....com>,
containers@...ts.linux-foundation.org, criu@...nvz.org,
linux-api@...r.kernel.org, x86@...nel.org,
Andrei Vagin <avagin@...il.com>
Subject: [PATCHv5 25/37] x86/vdso: Switch image on setns()/clone()
As it has been discussed on timens RFC, adding a new conditional branch
`if (inside_time_ns)` on VDSO for all processes is undesirable.
It will add a penalty for everybody as branch predictor may mispredict
the jump. Also there are instruction cache lines wasted on cmp/jmp.
Those effects of introducing time namespace are very much unwanted
having in mind how much work have been spent on micro-optimisation
vdso code.
Addressing those problems, there are two versions of VDSO's .so:
for host tasks (without any penalty) and for processes inside of time
namespace with clk_to_ns() that subtracts offsets from host's time.
Whenever a user does setns() or unshare(CLONE_TIMENS) followed
by clone(), change VDSO image in mm and zap VVAR/VDSO page tables.
They will be re-faulted with corresponding image and VVAR offsets.
Co-developed-by: Andrei Vagin <avagin@...il.com>
Signed-off-by: Andrei Vagin <avagin@...il.com>
Signed-off-by: Dmitry Safonov <dima@...sta.com>
---
arch/x86/entry/vdso/vma.c | 23 +++++++++++++++++++++++
arch/x86/include/asm/vdso.h | 1 +
kernel/time_namespace.c | 11 +++++++++++
3 files changed, 35 insertions(+)
diff --git a/arch/x86/entry/vdso/vma.c b/arch/x86/entry/vdso/vma.c
index 8a8211fd4cfc..91cf5a5c8c9e 100644
--- a/arch/x86/entry/vdso/vma.c
+++ b/arch/x86/entry/vdso/vma.c
@@ -25,6 +25,7 @@
#include <asm/cpufeature.h>
#include <clocksource/hyperv_timer.h>
#include <asm/page.h>
+#include <asm/tlb.h>
#if defined(CONFIG_X86_64)
unsigned int __read_mostly vdso64_enabled = 1;
@@ -266,6 +267,28 @@ static const struct vm_special_mapping vvar_mapping = {
.mremap = vvar_mremap,
};
+#ifdef CONFIG_TIME_NS
+int vdso_join_timens(struct task_struct *task)
+{
+ struct mm_struct *mm = task->mm;
+ struct vm_area_struct *vma;
+
+ if (down_write_killable(&mm->mmap_sem))
+ return -EINTR;
+
+ for (vma = mm->mmap; vma; vma = vma->vm_next) {
+ unsigned long size = vma->vm_end - vma->vm_start;
+
+ if (vma_is_special_mapping(vma, &vvar_mapping) ||
+ vma_is_special_mapping(vma, &vdso_mapping))
+ zap_page_range(vma, vma->vm_start, size);
+ }
+
+ up_write(&mm->mmap_sem);
+ return 0;
+}
+#endif
+
/*
* Add vdso and vvar mappings to current process.
* @image - blob to map
diff --git a/arch/x86/include/asm/vdso.h b/arch/x86/include/asm/vdso.h
index 03f468c63a24..ccf89dedd04f 100644
--- a/arch/x86/include/asm/vdso.h
+++ b/arch/x86/include/asm/vdso.h
@@ -45,6 +45,7 @@ extern struct vdso_image vdso_image_32;
extern void __init init_vdso_image(struct vdso_image *image);
extern int map_vdso_once(const struct vdso_image *image, unsigned long addr);
+extern int vdso_join_timens(struct task_struct *task);
#endif /* __ASSEMBLER__ */
diff --git a/kernel/time_namespace.c b/kernel/time_namespace.c
index 9807c5c90cb2..4b2eb92ad595 100644
--- a/kernel/time_namespace.c
+++ b/kernel/time_namespace.c
@@ -15,6 +15,7 @@
#include <linux/cred.h>
#include <linux/err.h>
#include <linux/mm.h>
+#include <asm/vdso.h>
ktime_t do_timens_ktime_to_host(clockid_t clockid, ktime_t tim,
struct timens_offsets *ns_offsets)
@@ -199,6 +200,7 @@ static void timens_put(struct ns_common *ns)
static int timens_install(struct nsproxy *nsproxy, struct ns_common *new)
{
struct time_namespace *ns = to_time_ns(new);
+ int ret;
if (!thread_group_empty(current))
return -EINVAL;
@@ -207,6 +209,10 @@ static int timens_install(struct nsproxy *nsproxy, struct ns_common *new)
!ns_capable(current_user_ns(), CAP_SYS_ADMIN))
return -EPERM;
+ ret = vdso_join_timens(current);
+ if (ret)
+ return ret;
+
get_time_ns(ns);
get_time_ns(ns);
put_time_ns(nsproxy->time_ns);
@@ -221,10 +227,15 @@ int timens_on_fork(struct nsproxy *nsproxy, struct task_struct *tsk)
{
struct ns_common *nsc = &nsproxy->time_ns_for_children->ns;
struct time_namespace *ns = to_time_ns(nsc);
+ int ret;
if (nsproxy->time_ns == nsproxy->time_ns_for_children)
return 0;
+ ret = vdso_join_timens(tsk);
+ if (ret)
+ return ret;
+
get_time_ns(ns);
put_time_ns(nsproxy->time_ns);
nsproxy->time_ns = ns;
--
2.22.0
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