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https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git
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550a77a74c
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
98 lines
2.4 KiB
ArmAsm
98 lines
2.4 KiB
ArmAsm
/* SPDX-License-Identifier: GPL-2.0 */
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#include <asm/vdso.h>
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/*
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* Linker script for vDSO. This is an ELF shared object prelinked to
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* its virtual address, and with only one read-only segment.
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* This script controls its layout.
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*/
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SECTIONS
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{
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/*
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* User/kernel shared data is before the vDSO. This may be a little
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* uglier than putting it after the vDSO, but it avoids issues with
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* non-allocatable things that dangle past the end of the PT_LOAD
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* segment.
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*/
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vvar_start = . - 4 * PAGE_SIZE;
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vvar_page = vvar_start;
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/* Place all vvars at the offsets in asm/vvar.h. */
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#define EMIT_VVAR(name, offset) vvar_ ## name = vvar_page + offset;
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#include <asm/vvar.h>
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#undef EMIT_VVAR
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pvclock_page = vvar_start + PAGE_SIZE;
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hvclock_page = vvar_start + 2 * PAGE_SIZE;
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timens_page = vvar_start + 3 * PAGE_SIZE;
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#undef _ASM_X86_VVAR_H
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/* Place all vvars in timens too at the offsets in asm/vvar.h. */
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#define EMIT_VVAR(name, offset) timens_ ## name = timens_page + offset;
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#include <asm/vvar.h>
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#undef EMIT_VVAR
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. = SIZEOF_HEADERS;
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.hash : { *(.hash) } :text
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.gnu.hash : { *(.gnu.hash) }
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.dynsym : { *(.dynsym) }
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.dynstr : { *(.dynstr) }
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.gnu.version : { *(.gnu.version) }
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.gnu.version_d : { *(.gnu.version_d) }
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.gnu.version_r : { *(.gnu.version_r) }
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.dynamic : { *(.dynamic) } :text :dynamic
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.rodata : {
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*(.rodata*)
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*(.data*)
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*(.sdata*)
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*(.got.plt) *(.got)
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*(.gnu.linkonce.d.*)
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*(.bss*)
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*(.dynbss*)
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*(.gnu.linkonce.b.*)
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} :text
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.note : { *(.note.*) } :text :note
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.eh_frame_hdr : { *(.eh_frame_hdr) } :text :eh_frame_hdr
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.eh_frame : { KEEP (*(.eh_frame)) } :text
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/*
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* Text is well-separated from actual data: there's plenty of
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* stuff that isn't used at runtime in between.
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*/
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.text : { *(.text*) } :text =0x90909090,
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.altinstructions : { *(.altinstructions) } :text
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.altinstr_replacement : { *(.altinstr_replacement) } :text
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/DISCARD/ : {
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*(.discard)
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*(.discard.*)
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*(__bug_table)
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}
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}
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/*
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* Very old versions of ld do not recognize this name token; use the constant.
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*/
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#define PT_GNU_EH_FRAME 0x6474e550
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/*
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* We must supply the ELF program headers explicitly to get just one
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* PT_LOAD segment, and set the flags explicitly to make segments read-only.
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*/
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PHDRS
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{
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text PT_LOAD FLAGS(5) FILEHDR PHDRS; /* PF_R|PF_X */
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dynamic PT_DYNAMIC FLAGS(4); /* PF_R */
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note PT_NOTE FLAGS(4); /* PF_R */
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eh_frame_hdr PT_GNU_EH_FRAME;
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}
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