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Message-ID: <CALCETrX7uaBBzi+S4pOwhjr2kJrSxiung2v_8weSiGuMjVvPKQ@mail.gmail.com>
Date: Wed, 31 Jul 2019 22:22:54 -0700
From: Andy Lutomirski <luto@...nel.org>
To: Dmitry Safonov <dima@...sta.com>
Cc: LKML <linux-kernel@...r.kernel.org>,
Dmitry Safonov <0x7f454c46@...il.com>,
Andrei Vagin <avagin@...nvz.org>,
Adrian Reber <adrian@...as.de>,
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>,
Linux Containers <containers@...ts.linux-foundation.org>,
criu@...nvz.org, Linux API <linux-api@...r.kernel.org>,
X86 ML <x86@...nel.org>, Andrei Vagin <avagin@...il.com>
Subject: Re: [PATCHv5 23/37] x86/vdso: Add offsets page in vvar
On Mon, Jul 29, 2019 at 2:58 PM Dmitry Safonov <dima@...sta.com> wrote:
>
> From: Andrei Vagin <avagin@...nvz.org>
>
> As modern applications fetch time from VDSO without entering the kernel,
> it's needed to provide offsets for userspace code inside time namespace.
>
> A page for timens offsets is allocated on time namespace construction.
> Put that page into VVAR for tasks inside timens and zero page for
> host processes.
>
> As VDSO code is already optimized as much as possible in terms of speed,
> any new if-condition in VDSO code is undesirable; the goal is to provide
> two .so(s), as was originally suggested by Andy and Thomas:
> - for host tasks with optimized-out clk_to_ns() without any penalty
> - for processes inside timens with clk_to_ns()
> For this purpose, define clk_to_ns() under CONFIG_TIME_NS.
>
> To eliminate any performance regression, clk_to_ns() will be called
> under static_branch with follow-up patches, that adds support for
> patching vdso.
>
> VDSO mappings are platform-specific, add Kconfig dependency for arch.
>
> Signed-off-by: Andrei Vagin <avagin@...il.com>
> Co-developed-by: Dmitry Safonov <dima@...sta.com>
> Signed-off-by: Dmitry Safonov <dima@...sta.com>
> ---
> arch/Kconfig | 5 +++
> arch/x86/Kconfig | 1 +
> arch/x86/entry/vdso/vdso-layout.lds.S | 9 ++++-
> arch/x86/entry/vdso/vdso2c.c | 3 ++
> arch/x86/entry/vdso/vma.c | 12 +++++++
> arch/x86/include/asm/vdso.h | 1 +
> init/Kconfig | 1 +
> lib/vdso/gettimeofday.c | 47 +++++++++++++++++++++++++++
> 8 files changed, 78 insertions(+), 1 deletion(-)
>
> diff --git a/arch/Kconfig b/arch/Kconfig
> index a7b57dd42c26..e43d27f510ec 100644
> --- a/arch/Kconfig
> +++ b/arch/Kconfig
> @@ -729,6 +729,11 @@ config HAVE_ARCH_NVRAM_OPS
> config ISA_BUS_API
> def_bool ISA
>
> +config ARCH_HAS_VDSO_TIME_NS
> + bool
> + help
> + VDSO can add time-ns offsets without entering kernel.
> +
> #
> # ABI hall of shame
> #
> diff --git a/arch/x86/Kconfig b/arch/x86/Kconfig
> index 222855cc0158..91615938b470 100644
> --- a/arch/x86/Kconfig
> +++ b/arch/x86/Kconfig
> @@ -81,6 +81,7 @@ config X86
> select ARCH_HAS_STRICT_MODULE_RWX
> select ARCH_HAS_SYNC_CORE_BEFORE_USERMODE
> select ARCH_HAS_UBSAN_SANITIZE_ALL
> + select ARCH_HAS_VDSO_TIME_NS
> select ARCH_HAVE_NMI_SAFE_CMPXCHG
> select ARCH_MIGHT_HAVE_ACPI_PDC if ACPI
> select ARCH_MIGHT_HAVE_PC_PARPORT
> diff --git a/arch/x86/entry/vdso/vdso-layout.lds.S b/arch/x86/entry/vdso/vdso-layout.lds.S
> index 93c6dc7812d0..ba216527e59f 100644
> --- a/arch/x86/entry/vdso/vdso-layout.lds.S
> +++ b/arch/x86/entry/vdso/vdso-layout.lds.S
> @@ -7,6 +7,12 @@
> * This script controls its layout.
> */
>
> +#ifdef CONFIG_TIME_NS
> +# define TIMENS_SZ PAGE_SIZE
> +#else
> +# define TIMENS_SZ 0
> +#endif
> +
> SECTIONS
> {
> /*
> @@ -16,7 +22,7 @@ SECTIONS
> * segment.
> */
>
> - vvar_start = . - 3 * PAGE_SIZE;
> + vvar_start = . - (3 * PAGE_SIZE + TIMENS_SZ);
> vvar_page = vvar_start;
>
> /* Place all vvars at the offsets in asm/vvar.h. */
> @@ -28,6 +34,7 @@ SECTIONS
>
> pvclock_page = vvar_start + PAGE_SIZE;
> hvclock_page = vvar_start + 2 * PAGE_SIZE;
> + timens_page = vvar_start + 3 * PAGE_SIZE;
>
> . = SIZEOF_HEADERS;
>
> diff --git a/arch/x86/entry/vdso/vdso2c.c b/arch/x86/entry/vdso/vdso2c.c
> index ce67370d14e5..7380908045c7 100644
> --- a/arch/x86/entry/vdso/vdso2c.c
> +++ b/arch/x86/entry/vdso/vdso2c.c
> @@ -75,12 +75,14 @@ enum {
> sym_vvar_page,
> sym_pvclock_page,
> sym_hvclock_page,
> + sym_timens_page,
> };
>
> const int special_pages[] = {
> sym_vvar_page,
> sym_pvclock_page,
> sym_hvclock_page,
> + sym_timens_page,
> };
>
> struct vdso_sym {
> @@ -93,6 +95,7 @@ struct vdso_sym required_syms[] = {
> [sym_vvar_page] = {"vvar_page", true},
> [sym_pvclock_page] = {"pvclock_page", true},
> [sym_hvclock_page] = {"hvclock_page", true},
> + [sym_timens_page] = {"timens_page", true},
> {"VDSO32_NOTE_MASK", true},
> {"__kernel_vsyscall", true},
> {"__kernel_sigreturn", true},
> diff --git a/arch/x86/entry/vdso/vma.c b/arch/x86/entry/vdso/vma.c
> index 2dc4f0b5481c..9bd66f84db5e 100644
> --- a/arch/x86/entry/vdso/vma.c
> +++ b/arch/x86/entry/vdso/vma.c
> @@ -14,6 +14,7 @@
> #include <linux/elf.h>
> #include <linux/cpu.h>
> #include <linux/ptrace.h>
> +#include <linux/time_namespace.h>
> #include <asm/pvclock.h>
> #include <asm/vgtod.h>
> #include <asm/proto.h>
> @@ -23,6 +24,7 @@
> #include <asm/desc.h>
> #include <asm/cpufeature.h>
> #include <clocksource/hyperv_timer.h>
> +#include <asm/page.h>
>
> #if defined(CONFIG_X86_64)
> unsigned int __read_mostly vdso64_enabled = 1;
> @@ -135,6 +137,16 @@ static vm_fault_t vvar_fault(const struct vm_special_mapping *sm,
> if (tsc_pg && vclock_was_used(VCLOCK_HVCLOCK))
> return vmf_insert_pfn(vma, vmf->address,
> vmalloc_to_pfn(tsc_pg));
> + } else if (sym_offset == image->sym_timens_page) {
> + struct time_namespace *ns = current->nsproxy->time_ns;
What, if anything, guarantees that all tasks in the mm share the same timens?
--Andy
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