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To support time namespaces in the VDSO with a minimal impact on regular non time namespace affected tasks, the namespace handling needs to be hidden in a slow path. The most obvious place is vdso_seq_begin(). If a task belongs to a time namespace then the VVAR page which contains the system wide VDSO data is replaced with a namespace specific page which has the same layout as the VVAR page. 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. The extra check in the case that vdso_data->seq is odd, e.g. a concurrent update of the VDSO data is in progress, is not really affecting regular tasks which are not part of a time namespace as the task is spin waiting for the update to finish and vdso_data->seq to become even again. If a time namespace task hits that code path, it invokes the corresponding time getter function which retrieves the real VVAR page, reads host time and then adds the offset for the requested clock which is stored in the special VVAR page. Allocate the time namespace page among VVAR pages and place vdso_data on it. Provide __arch_get_timens_vdso_data() helper for VDSO code to get the code-relative position of VVARs on that special 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/20191112012724.250792-23-dima@arista.com
56 lines
1.6 KiB
C
56 lines
1.6 KiB
C
/* SPDX-License-Identifier: GPL-2.0-only */
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/*
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* vvar.h: Shared vDSO/kernel variable declarations
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* Copyright (c) 2011 Andy Lutomirski
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*
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* A handful of variables are accessible (read-only) from userspace
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* code in the vsyscall page and the vdso. They are declared here.
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* Some other file must define them with DEFINE_VVAR.
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*
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* In normal kernel code, they are used like any other variable.
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* In user code, they are accessed through the VVAR macro.
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*
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* These variables live in a page of kernel data that has an extra RO
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* mapping for userspace. Each variable needs a unique offset within
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* that page; specify that offset with the DECLARE_VVAR macro. (If
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* you mess up, the linker will catch it.)
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*/
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#ifndef _ASM_X86_VVAR_H
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#define _ASM_X86_VVAR_H
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#ifdef EMIT_VVAR
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/*
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* EMIT_VVAR() is used by the kernel linker script to put vvars in the
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* right place. Also, it's used by kernel code to import offsets values.
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*/
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#define DECLARE_VVAR(offset, type, name) \
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EMIT_VVAR(name, offset)
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#else
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extern char __vvar_page;
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#define DECLARE_VVAR(offset, type, name) \
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extern type vvar_ ## name[CS_BASES] \
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__attribute__((visibility("hidden"))); \
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extern type timens_ ## name[CS_BASES] \
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__attribute__((visibility("hidden"))); \
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#define VVAR(name) (vvar_ ## name)
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#define TIMENS(name) (timens_ ## name)
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#define DEFINE_VVAR(type, name) \
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type name[CS_BASES] \
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__attribute__((section(".vvar_" #name), aligned(16))) __visible
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#endif
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/* DECLARE_VVAR(offset, type, name) */
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DECLARE_VVAR(128, struct vdso_data, _vdso_data)
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#undef DECLARE_VVAR
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#endif
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